Ravishankar Palanivelu

Interests

Research

Cell-cell communications in flowering plants

Teaching

Plant growth and development

Courses

Scholarly Contributions

Books

• Zhao, D., Chong, K., & Palanivelu, R. (2017). Molecular and Cellular Plant Reproduction. Frontiers Media SA. doi:10.3389/978-2-88945-211-8
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  Plant reproduction is essential not only for producing offspring but also for increasing crop quality and yield. Moreover, plant reproduction entails complex growth and developmental processes, which provide a variety of opportunities for elucidating fundamental principles in biology. The combinational employment of molecular genetic approaches and emerging technologies, such as florescence-based imaging techniques and next generation sequencing, has led to important progresses in plant reproduction using model plants, crops, and trees. This e-book compiles 31 articles, including 1 hypothesis and theory, 4 perspectives, 12 reviews, and 14 original research papers. We hope that this E-book will draw attention of all plant biologists to exciting advances in the field of plant reproduction and help solve remaining challenging questions in the future. We wish to express our appreciation to all the authors, reviewers, and the Frontiers editorial office for their excellent contributions that made the publication of this e-book possible.

Chapters

• Simek, K., Palanivelu, R., & Barnard, J. J. (2016). Branching Gaussian Processes with Applications to Spatiotemporal Reconstruction of 3D Trees. In Computer Vision – ECCV 2016(pp 177-193). Springer International Publishing.
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  In computer sciences, submission to conference proceedings are only published after a peer-review. This is a primary research article that was published in the conference proceedings after a peer-review.

Journals/Publications

• Huang, J., Yang, L., Yang, L., Wu, X., Cui, X., Zhang, L., Hui, J., Zhao, Y., Yang, H., Liu, S., Xu, Q., Pang, M., Guo, X., Cao, Y., Chen, Y., Ren, X., Lv, J., Yu, J., Ding, J., , Xu, G., et al. (2023). Stigma receptors control intraspecies and interspecies barriers in Brassicaceae. Nature, 614(7947), 303-308.
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  Flowering plants have evolved numerous intraspecific and interspecific prezygotic reproductive barriers to prevent production of unfavourable offspring. Within a species, self-incompatibility (SI) is a widely utilized mechanism that rejects self-pollen to avoid inbreeding depression. Interspecific barriers restrain breeding between species and often follow the SI × self-compatible (SC) rule, that is, interspecific pollen is unilaterally incompatible (UI) on SI pistils but unilaterally compatible (UC) on SC pistils. The molecular mechanisms underlying SI, UI, SC and UC and their interconnections in the Brassicaceae remain unclear. Here we demonstrate that the SI pollen determinant S-locus cysteine-rich protein/S-locus protein 11 (SCR/SP11) or a signal from UI pollen binds to the SI female determinant S-locus receptor kinase (SRK), recruits FERONIA (FER) and activates FER-mediated reactive oxygen species production in SI stigmas to reject incompatible pollen. For compatible responses, diverged pollen coat protein B-class from SC and UC pollen differentially trigger nitric oxide, nitrosate FER to suppress reactive oxygen species in SC stigmas to facilitate pollen growth in an intraspecies-preferential manner, maintaining species integrity. Our results show that SRK and FER integrate mechanisms underlying intraspecific and interspecific barriers and offer paths to achieve distant breeding in Brassicaceae crops.
• Huang, Y., Liu, L., Chai, M., Su, H., Ma, S., Liu, K., Tian, Y., Cao, Z., Xi, X., Zhu, W., Qi, J., Palanivelu, R., Qin, Y., & Cai, H. (2023). Epigenetic regulation of female germline development through ERECTA signaling pathway. The New phytologist, 240(3), 1015-1033.
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  Germline development is a key step in sexual reproduction. Sexual plant reproduction begins with the formation of haploid spores by meiosis of megaspore mother cells (MMCs). Although many evidences, directly or indirectly, show that epigenetics plays an important role in MMC specification, how it controls the commitment of the MMC to downstream stages of germline development is still unclear. Electrophoretic mobility shift assay (EMSA), western blot, immunofluorescence, and chromatin immunoprecipitation coupled with quantitative PCR analyses were performed. Genetic interactions between BZR1 transcription factor family and the SWR1-SDG2-ER pathway in the control of female germline development were further studied. The present findings showed in Arabidopsis that two epigenetic factors, the chromatin remodeling complex SWI2/SNF2-RELATED 1 (SWR1) and a writer for H3K4me3 histone modification SET DOMAIN GROUP 2 (SDG2), genetically interact with the ERECTA (ER) receptor kinase signaling pathway and regulate female germline development by restricting the MMC cell fate to a single cell in the ovule primordium and ensure that only that single cell undergoes meiosis and subsequent megaspore degeneration. We also showed that SWR1-SDG2-ER signaling module regulates female germline development by promoting the protein accumulation of BZR1 transcription factor family on the promoters of primary miRNA processing factors, HYPONASTIC LEAVES 1 (HYL1), DICER-LIKE 1 (DCL1), and SERRATE (SE) to activate their expression. Our study elucidated a Gene Regulation Network that provides new insights for understanding how epigenetic factors and receptor kinase signaling pathways function in concert to control female germline development in Arabidopsis.
• Palanivelu, R., Beilstein, M. A., Noble, J. A., Bielski, N. V., Liu, M. J., DeFalco, T. A., Stegmann, M., Nelson, A. D., McNamara, K., Sullivan, B., Dinh, K. K., Khuu, N., Hancock, S., Shiu, S., Zipfel, C., & Cheung, A. Y. (2022). Evolutionary analysis of the LORELEI gene family in plants reveals regulatory subfunctionalization. Plant Physiology, 190(4), 2539-2556. doi:10.1093/plphys/kiac444
• Uygun, S., Smith, S. E., Shiu, S., Seddon, A., Palanivelu, R., Noble, J. A., & Bright, A. (2022). The SEEL motif and members of the MYB-related REVEILLE transcription factor family are important for the expression of LORELEI in the synergid cells of the Arabidopsis female gametophyte.. Plant reproduction, 35(1), 61-76.
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  Synergid cells in the micropylar end of the female gametophyte are required for critical cell-cell signaling interactions between the pollen tube and the ovule that precede double fertilization and seed formation in flowering plants. LORELEI (LRE) encodes a putative GPI-anchored protein that is expressed primarily in the synergid cells, and together with FERONIA, a receptor-like kinase, it controls pollen tube reception by the receptive synergid cell. Still, how LRE expression is controlled in synergid cells remains poorly characterized. We identified candidate cis-regulatory elements enriched in LRE and other synergid cell-expressed genes. One of the candidate motifs ('TAATATCT') in the LRE promoter was an uncharacterized variant of the Evening Element motif that we named as the Short Evening Element-like (SEEL) motif. Deletion or point mutations in the SEEL motif of the LRE promoter resulted in decreased reporter expression in synergid cells, demonstrating that the SEEL motif is important for expression of LRE in synergid cells. Additionally, we found that LRE expression is decreased in the loss of function mutants of REVEILLE (RVE) transcription factors, which are clock genes known to bind the SEEL and other closely related motifs. We propose that RVE transcription factors regulate LRE expression in synergid cells by binding to the SEEL motif in the LRE promoter. Identification of cis-regulatory elements and transcription factors involved in the expression of LRE will serve as a foundation to characterize the gene regulatory networks in synergid cells.
• Cai, H., Liu, L., Zhang, M., Chai, M., Huang, Y., Chen, F., Yan, M., Su, Z., Henderson, I., Palanivelu, R., Chen, X., & Qin, Y. (2021). Spatiotemporal control of miR398 biogenesis, via chromatin remodeling and kinase signaling, ensures proper ovule development. The Plant cell, 33(5), 1530-1553.
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  The coordinated development of sporophytic and gametophytic tissues is essential for proper ovule patterning and fertility. However, the mechanisms regulating their integrated development remain poorly understood. Here, we report that the Swi2/Snf2-Related1 (SWR1) chromatin-remodeling complex acts with the ERECTA receptor kinase-signaling pathway to control female gametophyte and integument growth in Arabidopsis thaliana by inhibiting transcription of the microRNA gene MIR398c in early-stage megagametogenesis. Moreover, pri-miR398c is transcribed in the female gametophyte but is then translocated to and processed in the ovule sporophytic tissues. Together, SWR1 and ERECTA also activate ARGONAUTE10 (AGO10) expression in the chalaza; AGO10 sequesters miR398, thereby ensuring the expression of three AGAMOUS-LIKE (AGL) genes (AGL51, AGL52, and AGL78) in the female gametophyte. In the context of sexual organ morphogenesis, these findings suggest that the spatiotemporal control of miRNA biogenesis, resulting from coordination between chromatin remodeling and cell signaling, is essential for proper ovule development in Arabidopsis.
• Noble, J. A., Seddon, A., Uygun, S., Bright, A., Smith, S. E., Shiu, S. H., & Palanivelu, R. (2021). The SEEL motif and members of the MYB-related REVEILLE transcription factor family are important for the expression of LORELEI in the synergid cells of the Arabidopsis female gametophyte. Plant Reproduction.
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  Synergid cells in the micropylar end of the female gametophyte are required for critical cell-cell signaling interactions between the pollen tube and the ovule that precede double fertilization and seed formation in flowering plants. LORELEI (LRE) encodes a putative GPI-anchored protein that is expressed primarily in the synergid cells, and together with FERONIA, a receptor-like kinase, it controls pollen tube reception by the receptive synergid cell. Still, how LRE expression is controlled in synergid cells remains poorly characterized. We identified candidate cis-regulatory elements enriched in LRE and other synergid cell-expressed genes. One of the candidate motifs ('TAATATCT') in the LRE promoter was an uncharacterized variant of the Evening Element motif that we named as the Short Evening Element-like (SEEL) motif. Deletion or point mutations in the SEEL motif of the LRE promoter resulted in decreased reporter expression in synergid cells, demonstrating that the SEEL motif is important for expression of LRE in synergid cells. Additionally, we found that LRE expression is decreased in the loss of function mutants of REVEILLE (RVE) transcription factors, which are clock genes known to bind the SEEL and other closely related motifs. We propose that RVE transcription factors regulate LRE expression in synergid cells by binding to the SEEL motif in the LRE promoter. Identification of cis-regulatory elements and transcription factors involved in the expression of LRE will serve as a foundation to characterize the gene regulatory networks in synergid cells.
• Palanivelu, R., Sze, H., Harper, J. F., & Johnson, M. A. (2021). Holistic insights from pollen omics: co-opting stress-responsive genes and ER-mediated proteostasis for male fertility. Plant Physiology, 187(4), 2361-2380. doi:10.1093/plphys/kiab463
• Sze, H., Palanivelu, R., Harper, J. F., & Johnson, M. A. (2021). Holistic insights from pollen omics: Co-opting stress-responsive genes and ER-mediated proteostasis for male fertility. Plant physiology, 187(4), 2361-2380.
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  Sexual reproduction in flowering plants takes place without an aqueous environment. Sperm are carried by pollen through air to reach the female gametophyte, though the molecular basis underlying the protective strategy of the male gametophyte is poorly understood. Here we compared the published transcriptomes of Arabidopsis thaliana pollen, and of heat-responsive genes, and uncovered insights into how mature pollen tolerates desiccation, while developing and germinating pollen are vulnerable to heat stress. Germinating pollen expresses molecular chaperones or 'heat shock proteins' in the absence of heat stress. Furthermore, pollen tubes that grew through pistils at basal temperature showed induction of the ER stress response, which is a characteristic of stressed vegetative tissues. Recent studies show mature pollen contains mRNA-protein aggregates that resemble 'stress' granules triggered by heat or other stresses to protect cells. Based on these observations, we postulate that mRNA-protein particles are formed in maturing pollen in response to developmentally programmed dehydration. Dry pollen can withstand harsh conditions as it is dispersed in air. We propose that, when pollen lands on a compatible pistil and hydrates, mRNAs stored in particles are released, aided by molecular chaperones, to become translationally active. Pollen responds to osmotic, mechanical, oxidative and peptide cues that promote ER-mediated proteostasis and membrane trafficking for tube growth and sperm discharge. Unlike vegetative tissues, pollen depends on stress-protection strategies for its normal development and function. Thus, heat stress during reproduction likely triggers changes that interfere with the normal stress responses, thereby compromising male fertility. This holistic perspective provides a framework to understand the basis of heat-tolerant strains in the reproduction of crops.
• Palanivelu, R., & Desnoyer, N. (2020). Bridging the GAPs in plant reproduction: a comparison of plant and animal GPI-anchored proteins.. Plant reproduction, 33(3-4), 129-142. doi:10.1007/s00497-020-00395-9
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  Glycosylphosphatidylinositol (GPI)-anchored proteins (GAPs) are a unique type of membrane-associated proteins in eukaryotes. GPI and GAP biogenesis and function have been well studied in non-plant models and play an important role in the fertility of mouse sperm and egg. Although GPI and GAP biogenesis and function in plants are less known, they are critical for flowering plant reproduction because of their essential roles in the fertility of the male and female gametophytes. In Eukaryotes, GPI, a glycolipid molecule, can be post-translationally attached to proteins to serve as an anchor in the plasma membrane. GPI-anchoring, compared to other modes of membrane attachment and lipidation processes, localizes proteins to the extracellular portion of the plasma membrane and confers several unique attributes including specialized sorting during secretion, molecular painting onto membranes, and enzyme-mediated release of protein through anchor cleavage. While the biosynthesis, structure, and role of GPI are mostly studied in mammals, yeast and protists, the function of GPI and GAPs in plants is being discovered, particularly in gametophyte development and function. Here, we review GPI biosynthesis, protein attachment, and remodeling in plants with insights about this process in mammals. Additionally, we summarize the reproductive phenotypes of all loss of function mutations in Arabidopsis GPI biosynthesis and GAP genes and compare these to the reproductive phenotypes seen in mice to serve as a framework to identify gaps in our understanding of plant GPI and GAPs. In addition, we present an analysis on the gametophyte expression of all Arabidopsis GAPs to assist in further research on the role of GPI and GAPs in all aspects of the gametophyte generation in the life cycle of a plant.
• Palanivelu, R., & Noble, J. A. (2020). Workflow to Characterize Mutants with Reproductive Defects.. Methods in molecular biology (Clifton, N.J.), 2160, 109-128. doi:10.1007/978-1-0716-0672-8_8
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  Reverse genetics approaches for characterizing phenotypes of mutants in a gene of interest (GOI) require thorough genotyping and phenotypic analysis. However, special challenges are encountered when a GOI is expressed in reproductive tissues: a variety of assays are required to characterize the phenotype and a mutant may show sporophytic and/or gametophytic defects in male and/or female reproductive tissues, which are structurally and functionally intertwined. Here, we present a streamlined workflow to characterize mutants with reproductive defects, primarily using Arabidopsis as a model, which can also be adapted to characterize mutants in other flowering plants. Procedures described here can be used to distinguish different kinds of reproductive defects and pinpoint the defective reproductive step(s) in a mutant. Although our procedures emphasize the characterization of mutants with male reproductive defects, they can nevertheless be used to identify female reproductive defects, as those defects could manifest alongside, and sometimes require, male reproductive tissues.
• Palanivelu, R., Jong, E., Howard, G., & Desnoyer, N. (2020). AtPIG-S, a predicted Glycosylphosphatidylinositol Transamidase subunit, is critical for pollen tube growth in Arabidopsis.. BMC plant biology, 20(1), 380. doi:10.1186/s12870-020-02587-x
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  Glycosylphosphatidylinositol (GPI) addition is one of the several post-translational modifications to proteins that increase their affinity for membranes. In eukaryotes, the GPI transamidase complex (GPI-T) catalyzes the attachment of pre-assembled GPI anchors to GPI-anchored proteins (GAPs) through a transamidation reaction. A mutation in AtGPI8 (gpi8-2), the putative catalytic subunit of GPI-T in Arabidopsis, is transmitted normally through the female gametophyte (FG), indicating the FG tolerates loss of GPI transamidation. In contrast, gpi8-2 almost completely abolishes male gametophyte (MG) function. Still, the unexpected finding that gpi8-2 FGs function normally requires further investigation. Additionally, specific developmental defects in the MG caused by loss of GPI transamidation remain poorly characterized..Here we investigated the effect of loss of AtPIG-S, another GPI-T subunit, in both gametophytes. Like gpi8-2, we showed that a mutation in AtPIG-S (pigs-1) disrupted synergid localization of LORELEI (LRE), a putative GAP critical for pollen tube reception by the FG. Still, pigs-1 is transmitted normally through the FG. Conversely, pigs-1 severely impaired male gametophyte (MG) function during pollen tube emergence and growth in the pistil. A pPIGS:GFP-PIGS transgene complemented these MG defects and enabled generation of pigs-1/pigs-1 seedlings. However, the pPIGS:GFP-PIGS transgene seemingly failed to rescue the function of AtPIG-S in the sporophyte, as pigs-1/pigs-1, pPIGS:GFP-PIGS seedlings died soon after germination..Characterization of pigs-1 provided further evidence that the FG tolerates loss of GPI transamidation more than the MG and that the MG compared to the FG may be a better haploid system to study the role of GPI-anchoring. Pigs-1 pollen develops normally and thus represent a tool in which GPI anchor biosynthesis and transamidation of GAPs have been uncoupled, offering a potential way to study free GPI in plant development. While previously reported male fertility defects of GPI biosynthesis mutants could have been due either to loss of GPI or GAPs lacking the GPI anchor, our results clarified that the loss of mature GAPs underlie male fertility defects of GPI-deficient pollen grains, as pigs-1 is defective only in the downstream transamidation step.
• Johnson, M. A., Harper, J. F., & Palanivelu, R. (2019). A Fruitful Journey: Pollen Tube Navigation from Germination to Fertilization. Annual review of plant biology, 70, 809-837.
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  In flowering plants, pollen tubes undergo tip growth to deliver two nonmotile sperm to the ovule where they fuse with an egg and central cell to achieve double fertilization. This extended journey involves rapid growth and changes in gene activity that manage compatible interactions with at least seven different cell types. Nearly half of the genome is expressed in haploid pollen, which facilitates genetic analysis, even of essential genes. These unique attributes make pollen an ideal system with which to study plant cell-cell interactions, tip growth, cell migration, the modulation of cell wall integrity, and gene expression networks. We highlight the signaling systems required for pollen tube navigation and the potential roles of Ca signals. The dynamics of pollen development make sexual reproduction highly sensitive to heat stress. Understanding this vulnerability may generate strategies to improve seed crop yields that are under threat from climate change.
• Jones, D. S., Liu, X., Willoughby, A. C., Smith, B. E., Palanivelu, R., & Kessler, S. A. (2018). Cellular distribution of secretory pathway markers in the haploid synergid cells of Arabidopsis thaliana. The Plant journal, 94(1), 192-202. doi:10.1111/tpj.13848
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  In flowering plants, cell-cell communication plays a key role in reproductive success, as both pollination and fertilization require pathways that regulate interactions between many different cell types. Some of the most critical of these interactions are those between the pollen tube (PT) and the embryo sac, which ensure the delivery of sperm cells required for double fertilization. Synergid cells function to attract the PT through secretion of small peptides and in PT reception via membrane-bound proteins associated with the endomembrane system and the cell surface. While many synergid-expressed components regulating PT attraction and reception have been identified, few tools exist to study the localization of membrane-bound proteins and the components of the endomembrane system in this cell type. In this study, we describe the localization and distribution of seven fluorescent markers that labelled components of the secretory pathway in synergid cells of Arabidopsis thaliana. These markers were used in co-localization experiments to investigate the subcellular distribution of the two PT reception components LORELEI, a GPI-anchored surface protein, and NORTIA, a MILDEW RESISTANCE LOCUS O protein, both found within the endomembrane system of the synergid cell. These secretory markers are useful tools for both reproductive and cell biologists, enabling the analysis of membrane-associated trafficking within a haploid cell actively involved in polar transport.
• Palanivelu, R., Jones, D. S., Liu, X., Willoughby, A. C., Smith, B. E., & Kessler, S. A. (2018). Cellular distribution of secretory pathway markers in the haploid synergid cells of Arabidopsis thaliana. The Plant Journal, 94(1), 192-202. doi:10.1111/tpj.13848
• Zhao, L., Cai, H., Su, Z., Wang, L., Huang, X., Zhang, M., Chen, P., Dai, X., Zhao, H., Palanivelu, R., Chen, X., & Qin, Y. (2018). KLU suppresses megasporocyte cell fate through SWR1-mediated activation of WRKY28 expression in Arabidopsis. PNAS, 115(3), E526–E535. doi:10.1073/pnas.1716054115
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  In flowering plants, the female germ line begins as a single cell known as the megaspore mother cell (MMC) in each ovule. The mechanisms that restrict MMC fate to a single cell remain largely unknown. We show that the Arabidopsis cytochrome P450 gene KLU acts through the chromatin remodeling complex SWR1 to promote WRKY28 expression in ovule primordia. We show that WRKY28 is expressed in a few somatic cells surrounding the MMC and is required to inhibit these cells from acquiring the MMC-like cell fate. Consistent with non–cell-autonomous KLU activity, KLU-expressing cells and WRKY28-expressing cells are neither identical nor adjacently positioned. Our study demonstrates that cell–cell interactions involving only somatic cells in ovule primordia ensure the specification of a single MMC.
• Palanivelu, R., Noble, J. A., Wang, Y., Tsukamoto, T., Liu, X., & Mosher, R. A. (2017). Arabidopsis LORELEI, a Maternally Expressed Imprinted Gene, Promotes Early Seed Development. Plant Physiology, 175(2), 758-773. doi:10.1104/pp.17.00427
• Palanivelu, R., Zhao, L., Cai, H., Su, Z., Wang, L., Huang, X., Zhang, M., Chen, P., Dai, X., Zhao, H., Chen, X., & Qin, Y. (2017). KLU suppresses megasporocyte cell fate through SWR1-mediated activation of WRKY28 expression in Arabidopsis. Proceedings of the National Academy of Sciences, 115(3). doi:10.1073/pnas.1716054115
• Wang, Y., Tsukamoto, T., Noble, J., Liu, X., Harris, R. A., & Palanivelu, R. (2017). Arabidopsis LORELEI, a Maternally Expressed Imprinted Gene, Promotes Early Seed Development. Plant Physiology, 175(2), 758-773. doi:10.1104/pp.17.00427
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  In flowering plants, the female gametophyte controls pollen tube reception immediately before fertilization and regulates seed development immediately after fertilization, although the controlling mechanisms remain poorly understood. Previously, we showed that LORELEI (LRE), which encodes a putative glycosylphosphatidylinositol-anchored membrane protein, is critical for pollen tube reception by the female gametophyte before fertilization and the initiation of seed development after fertilization. Here, we show that LRE is expressed in the synergid, egg, and central cells of the female gametophyte and in the zygote and proliferating endosperm of the Arabidopsis (Arabidopsis thaliana) seed. Interestingly, LRE expression in the developing seeds was primarily from the matrigenic LRE allele, indicating that LRE expression is imprinted. However, LRE was biallelically expressed in 8-d-old seedlings, indicating that the patrigenic allele does not remain silenced throughout the sporophytic generation. Regulation of imprinted LRE expression is likely novel, as LRE was not expressed in pollen or pollen tubes of mutants defective for MET1, DDM1, RNA-dependent DNA methylation, or MSI-dependent histone methylation. Additionally, the patrigenic LRE allele inherited from these mutants was not expressed in seeds. Surprisingly, and contrary to the predictions of the parental conflict hypothesis, LRE promotes growth in seeds, as loss of the matrigenic but not the patrigenic LRE allele caused delayed initiation of seed development. Our results showed that LRE is a rare imprinted gene that functions immediately after double fertilization and supported the model that a passage through the female gametophyte establishes monoalleleic expression of LRE in seeds and controls early seed development.
• Zhao, D., Palanivelu, R., & Chong, K. (2017). Editorial: Molecular and Cellular Plant Reproduction.. Frontiers in plant science, 8, 199. doi:10.3389/fpls.2017.00199
• Liu, X., Castro, C., Wang, Y., Noble, J., Ponvert, N., Bundy, M., Hoel, C., Shpak, E., & Palanivelu, R. (2016). LORELEI Function in Pollen Tube Reception at the Interface of the Synergid Cell and the Pollen Tube Requires the Modified Eight-Cysteine Motif, but not the GPI Anchor Addition Domains. Plant Cell, 28(5), 1035-1052.
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  This paper was profiled in "In Brief" section in the Plant Cell. “Sticking the Landing: Probing the Roles of LORELEI in Pollen Tube Reception” by Jennifer Lockhart. Plant Cell. (http://www.plantcell.org/content/early/2016/04/15/tpc.16.00308.full.pdf+html?sid=0a4a9ffe-ecd8-4214-babf-6d6ee2d11980)*Our image submission was also chosen as the cover of the May 2016 issue of The Plant Cell (image above), in which this article was published. (.jpg image file attached in this entry)
• Qin, Y., Leydon, A. R., Manziello, A., Pandey, R., Mount, D., Denic, S., Vasic, B., Johnson, M. A., & Palanivelu, R. (2016). Correction: Penetration of the Stigma and Style Elicits a Novel Transcriptome in Pollen Tubes, Pointing to Genes Critical for Growth in a Pistil.. PLoS genetics, 12(7), e1006210. doi:10.1371/journal.pgen.1006210
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  [This corrects the article DOI: 10.1371/journal.pgen.1000621.].
• Wang, Y., Shpak, E. D., Ponvert, N. D., Palanivelu, R., Noble, J. A., Liu, X., Hoel, C. R., Castro, C. A., & Bundy, M. G. (2016). The Role of LORELEI in Pollen Tube Reception at the Interface of the Synergid Cell and Pollen Tube Requires the Modified Eight-Cysteine Motif and the Receptor-Like Kinase FERONIA.. The Plant cell, 28(5), 1035-52. doi:10.1105/tpc.15.00703
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  In angiosperms, pollen tube reception by the female gametophyte is required for sperm release and double fertilization. In Arabidopsis thaliana lorelei (lre) mutants, pollen tube reception fails in most female gametophytes, which thus remain unfertilized. LRE encodes a putative glycosylphosphatidylinositol (GPI)-anchored surface protein with a modified eight-cysteine motif (M8CM). LRE fused to citrine yellow fluorescent protein (LRE-cYFP) remains functional and localizes to the synergid plasma membrane-rich filiform apparatus, the first point of contact between the pollen tube and the female gametophyte. Structure-function analysis using LRE-cYFP showed that the role of LRE in pollen tube reception requires the M8CM, but not the domains required for GPI anchor addition. Consistently, LRE-cYFP-TM, where GPI anchor addition domains were replaced with a single-pass transmembrane domain, fully complemented the pollen tube reception defect in lre-7 female gametophytes. Ectopically expressed and delivered LRE-cYFP from pollen tubes could non-cell-autonomously complement the pollen tube reception defect in lre female gametophytes, only if they expressed FERONIA. Additionally, pollen tube-expressing LRE variants lacking domains critical for GPI anchor addition also rescued lre female gametophyte function. Therefore, LRE and FERONIA jointly function in pollen tube reception at the interface of the synergid cell and pollen tube.
• Leydon, A. R., Tsukamoto, T., Dunatunga, D., Qin, Y., Johnson, M. A., & Palanivelu, R. (2015). Pollen Tube Discharge Completes the Process of Synergid Degeneration That Is Initiated by Pollen Tube-Synergid Interaction in Arabidopsis. Plant Physiology, 169, 485-496.
• Palanivelu, R., Yadegari, R., & Qin, Y. (2015). ACTIN-RELATED PROTEIN 6 regulates DISRUPTED MEIOTIC cDNA 1 gene expression in Arabidopsis thaliana ovules. Molecular Reproduction and Development, 82(7-8), 499-499. doi:10.1002/mrd.22472
• Qin, Y., Yadegari, R., & Palanivelu, R. (2015). ACTIN-RELATED PROTEIN 6 regulates DISRUPTED MEIOTIC cDNA 1 gene expression in Arabidposis thaliana ovules. Molecular Reproduction and Development, 82, 499--499.
• Palanivelu, R., Yadegari, R., Smith, S., Qin, Y., Zhao, L., Skaggs, M. I., Andreuzza, S., Tsukamoto, T., Panoli, A., Wallace, K. N., Siddiqi, I., & Yang, Z. (2014). ACTIN-RELATED PROTEIN6 Regulates Female Meiosis by Modulating Meiotic Gene Expression in Arabidopsis. The Plant Cell, 26(4), 1612-1628. doi:10.1105/tpc.113.120576
• Qin, Y., Zhao, L., Skaggs, M. I., Andreuzza, S., Tsukamoto, T., Panoli, A., Wallace, K. N., Smith, S. E., Siddiqi, I., Yang, Z., Yadegari, R., & Palanivelu, R. (2014). ARP6 Controls Female Meiosis In Arabidopsis Partly By Activating DMC1 Expression In Megasporocytes. The Plant Cell, 26(4), 1612-1628.
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  Correspondence: RY and RP. F1000 article recommendation: http://f1000.com/prime/718352855.
• Yu, G., Zou, J., Feng, J., Peng, X., Wu, J., Wu, Y., Palanivelu, R., & Sun, M. (2014). Exogenous γ-aminobutyric acid (GABA) affects pollen tube growth via modulating putative Ca2+-permeable membrane channels and is coupled to negative regulation on glutamate decarboxylase. Journal of Experimental Botany, 65(12), 3235-48.
• Bashir, M. H., Palanivelu, R. -., Lui, J. H., Naclerio, R. M., & Preuss, D. (2013). Pollen Lipidomics: Lipid Profiling Exposes a Notable Diversity in 22 Allergenic Pollen and Potential Biomarkers of the Allergic Immune Response. PLOS ONE, 8(2), e57566.
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  Manuscript based on postdoctoral work
• Cheung, A., Palanivelu, R. -., Tang, W., Xue, H., & Yang, W. (2013). Pollen and plant reproduction biology: blooming from East to West. Molecular Plant, 6(4).
• Leydon, A. R., Beale, K. M., Woroniecka, K., Castner, E., Chen, J., Horgan, C., Palanivelu, R., & Johnson, M. A. (2013). Three MYB transcription factors control pollen tube differentiation required for sperm release. Current Biology, 23(13), 1209-1214.
• Palanivelu, R., & Tsukamoto, T. (2012). Pathfinding in angiosperm reproduction: Pollen tube guidance by pistils ensures successful double fertilization. Wiley Interdisciplinary Reviews: Developmental Biology, 1(1), 96-113.
• Veerappan, V., Wang, J., Kang, M., Lee, J., Tang, Y., Jha, A. K., Shi, H., Palanivelu, R., & Allen, R. D. (2012). A novel HSI2 mutation in Arabidopsis affects the PHD-like domain and leads to derepression of seed-specific gene expression. Planta, 236(1), 1-17.
• Brau, E., Barnard, J. J., Palanivelu, R. -., Dunatunga, D., Tsukamoto, T., & Lee, P. (2011). A generative statistical model for tracking multiple smooth trajectories of pollen tubes. Proceedings of the IEEE Computer Vision and Pattern Recognition, 1137-1144.
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  doi: 10.1109/CVPR.2011.5995736
• Palanivelu, R. -. (2011). Targeted growth of pollen tubes to ovules prior to completing fertilization. Molecular Reproduction and Development, 78(12), 893.
• Qin, Y., Wysocki, R. J., Somogyi, A., Feinstein, Y., Franco, J. Y., Tsukamoto, T., Dunatunga, D., Levy, C., Smith, S. E., Simpson, R., Gang, D., Johnson, M. A., & Palanivelu, R. -. (2011). Sulfinylated azadecalins act as functional mimics of a pollen germination stimulant in Arabidopsis pistils. The Plant journal : for cell and molecular biology, 68(5).
• Renault, H., Amrani, A. E., Palanivelu, R., Updegraff, E. P., Agns, Y. u., Renou, J., Preuss, D., Bouchereau, A., & Deleu, C. (2011). GABA accumulation causes cell elongation defects and a decrease in expression of genes encoding secreted and cell wall-related proteins in Arabidopsis thaliana. Plant and Cell Physiology, 52(5), 894-908.
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  PMID: 21471118;PMCID: PMC3093128;Abstract: GABA (γ-aminobutyric acid), a non-protein amino acid, is a signaling factor in many organisms. In plants, GABA is known to accumulate under a variety of stresses. However, the consequence of GABA accumulation, especially in vegetative tissues, remains poorly understood. Moreover, gene expression changes as a consequence of GABA accumulation in plants are largely unknown. The pop2 mutant, which is defective in GABA catabolism and accumulates GABA, is a good model to examine the effects of GABA accumulation on plant development. Here, we show that the pop2 mutants have pollen tube elongation defects in the transmitting tract of pistils. Additionally, we observed growth inhibition of primary root and dark-grown hypocotyl, at least in part due to cell elongation defects, upon exposure to exogenous GABA. Microarray analysis of pop2-1 seedlings grown in GABA-supplemented medium revealed that 60 of genes whose expression decreased encode secreted proteins. Besides, functional classification of genes with decreased expression in the pop2-1 mutant showed that cell wall-related genes were significantly enriched in the microarray data set, consistent with the cell elongation defects observed in pop2 mutants. Our study identifies cell elongation defects caused by GABA accumulation in both reproductive and vegetative tissues. Additionally, our results show that genes that encode secreted and cell wall-related proteins may mediate some of the effects of GABA accumulation. The potential function of GABA as a growth control factor under stressful conditions is discussed. © 2011 The Author.
• Renault, H., El, A. A., Palanivelu, R. -., Updegraff, E., Yu, A., Renou, J., Preuss, D., Bouchereau, A., & Deleu, C. (2011). GABA accumulation causes cell elongation defects and decrease in expression of genes encoding secreted and cell wall-related proteins in Arabidopsis thaliana. Plant Cell Physiology, 52(5), 894-908.
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  Manuscript based on postdoctoral work
• Yetisen, A., Jiang, L., Cooper, J., Qin, Y., Palanivelu, R. -., & Zohar, Y. -. (2011). A microsystem-based assay for studying pollen tube guidance in plant reproduction. Journal of Micromechanics and Microengineering, 21.
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  Correspondence: RP and YZ
• Palanivelu, R., & Johnson, M. A. (2010). Functional genomics of pollen tube–pistil interactions in Arabidopsis. Biochemical Society Transactions, 38(2), 593-597. doi:10.1042/bst0380593
• Palanivelu, R., & Johnson, M. A. (2010). Functional genomics of pollen tube-pistil interactions in Arabidopsis. Biochemical Society Transactions, 38(2), 593-597.
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  PMID: 20298227;Abstract: The pollen tube represents an attractive model system for functional genomic analysis of the cell-cell interactions that mediate guided cellular growth. The pollen tube extends through pistil tissues and responds to guidance cues that direct the tube towards an ovule, where it releases sperm for fertilization. Pollen is readily isolated from anthers, where it is produced, and can be induced to produce a tube in vitro. Interestingly, pollen tube growth is significantly enhanced in pistils, and pollen tubes are rendered competent to respond to guidance cues after growth in a pistil. This potentiation of the pollen tube by the pistil suggested that pollen tubes alter their gene-expression programme in response to their environment. Recently, the transcriptomes of pollen tubes grown in vitro or through pistil tissues were determined. Signi-ficant changes in the transcriptome were found to accompany growth in vitro and through the pistil tissues. Reverse genetic analysis of pollen-tube-induced genes identified a new set of factors critical for pollen tube extension and navigation of the pistil environment. Recent advances reviewed in the present paper suggest that functional genomic analysis of pollen tubes has the potential to uncover the regulatory networks that shape the genetic architecture of the pollen tube as it responds to migratory cues produced by the pistil. ©The Authors.
• Tsukamoto, T., & Palanivelu, R. (2010). Loss of LORELEI function in the pistil delays initiation but does not affect embryo development in Arabidopsis thaliana. Plant Signaling and Behavior, 5(11).
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  PMID: 21051955;PMCID: PMC3115263;Abstract: Double fertilization, uniquely observed in plants, requires successful sperm cell delivery by the pollen tube to the female gametophyte, followed by migration, recognition and fusion of the two sperm cells with two female gametic cells. The female gametophyte not only regulates these steps but also controls the subsequent initiation of seed development. Previously, we reported that loss of LORELEI, which encodes a putative glycosylphosphatidylinositol (GPI)-anchored protein, in the female reproductive tissues causes a delay in initiation of seed development. From these studies, however, it was unclear if embryos derived from fertilization of lre-5 gametophytes continued to lag behind wild type during seed development. Additionally, it was not determined if the delay in initiation of seed development had any lingering effects during seed germination. Finally, it was not known if loss of LORELEI function affects seedling development given that LORELEI is expressed in eight-day-old seedlings. Here, we showed that despite a delay in initiation, lre-5/lre-5 embryos recover, becoming equivalent to the developing wild-type embryos beginning at 72 hours after pollination. Additionally, lre-5/lre-5 seed germination, and seedling and root development are indistinguishable from wild type indicating that loss of LORELEI is tolerated, at least under standard growth conditions, in vegetative tissues. © 2010 Landes Bioscience.
• Tsukamoto, T., Qin, Y., Huang, Y., Dunatunga, D., & Palanivelu, R. (2010). A role for LORELEI, a putative glycosylphosphatidylinositol-anchored protein, in Arabidopsis thaliana double fertilization and early seed development. Plant Journal, 62(4), 571-588.
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  PMID: 20163554;Abstract: In plants, double fertilization requires successful sperm cell delivery into the female gametophyte followed by migration, recognition and fusion of the two sperm cells with two female gametes. We isolated a null allele (lre-5) of LORELEI, which encodes a putative glycosylphosphatidylinositol (GPI)-anchored protein implicated in reception of the pollen tube by the female gametophyte. Although most lre-5 female gametophytes do not allow pollen tube reception, in those that do, early seed development is delayed. A fraction of lre-5/lre-5 seeds underwent abortion due to defect(s) in the female gametophyte. The aborted seeds contained endosperm but no zygote/embryo, reminiscent of autonomous endosperm development in the pollen tube reception mutants scylla and sirene. However, unpollinated lre-5/lre-5 ovules did not initiate autonomous endosperm development and endosperm development in aborted seeds began after central cell fertilization. Thus, the egg cell probably remained unfertilized in aborted lre-5/lre-5 seeds. The lre-5/lre-5 ovules that remain undeveloped due to defective pollen tube reception did not induce synergid degeneration and repulsion of supernumerary pollen tubes. In ovules, LORELEI is expressed during pollen tube reception, double fertilization and early seed development. Null mutants of LORELEI-like-GPI-anchored protein 1 (LLG1), the closest relative of LORELEI among three Arabidopsis LLG genes, are fully fertile and did not enhance reproductive defects in lre-5/lre-5 pistils, suggesting that LLG1 function is not redundant with that of LORELEI in the female gametophyte. Our results show that, besides pollen tube reception, LORELEI also functions during double fertilization and early seed development. © 2010 Blackwell Publishing Ltd.
• Palanivelu, R., Palanivelu, R. -., Qin, Y., Leydon, A. R., Manziello, A., Pandey, R., Mount, D., Denic, S., Vasic, B., & Johnson, M. A. (2009). Penetration of the stigma and style elicits a novel transcriptome in pollen tubes, pointing to genes critical for growth in a pistil. PLoS Genetics, 5(8).
• Vasic, B., Vasic, B., Palanivelu, R., Denic, S. Z., & Charalambous, C. D. (2009). Robust control of uncertain context-sensitive probabilistic Boolean networks.. IET systems biology, 3(4), 279-95. doi:10.1049/iet-syb.2008.0121
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  Uncertainty is an intrinsic phenomenon in control of gene regulatory networks (GRNs). The presence of uncertainty is related to impreciseness of GRN models due to: (1) Errors caused by imperfection of measurement devices and (2) Models' inability to fully capture a complex structure of the GRN. Consequently, there is a discrepancy between actual behaviour of the GRN and what is predicted by its mathematical model. This can result in false control signals, which can drive a cell to an undesirable state. To address the problem of control under uncertainties, a risk-sensitive control paradigm is proposed. Robustness is accomplished by minimisation of the mean exponential cost as opposed to, for instance, minimisation of the mean square cost by risk-neutral controllers. The authors derive an optimal risk-sensitive controller when a GRN is modelled by a context-sensitive probabilistic Boolean network (CSPBN). By using a relation between the relative entropy and free-energy, a relative stability of the cost achieved by the risk-sensitive controller is demonstrated when the distribution of the CSPBN attractors is perturbed, as opposed to the cost of the risk-neutral controller that exhibits increase. The use of the relation between the relative entropy and free-energy to analyse the influence of a particular attractor on the robustness of the controller is studied. The efficiency of the risk-sensitive controller is tested for the CSPBN obtained from the study of malignant melanoma.
• Sandaklie-Nikolova, L., Palanivelu, R., King, E. J., Copenhaver, G. P., & Drews, G. N. (2007). Synergid cell death in Arabidopsis is triggered following direct interaction with the pollen tube. Plant Physiology, 144(4), 1753-1762.
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  PMID: 17545508;PMCID: PMC1949904;Abstract: During angiosperm reproduction, one of the two synergid cells within the female gametophyte undergoes cell death prior to fertilization. The pollen tube enters the female gametophyte by growing into the synergid cell that undergoes cell death and releases its two sperm cells within the degenerating synergid cytoplasm to effect double fertilization. In Arabidopsis (Arabidopsis thaliana) and many other species, synergid cell death is dependent upon pollination. However, the mechanism by which the pollen tube causes synergid cell death is not understood. As a first step toward understanding this mechanism, we defined the temporal relationship between pollen tube arrival at the female gametophyte and synergid cell death in Arabidopsis. Using confocal laser scanning microscopy, light microscopy, transmission electron microscopy, and real-time observation of these two events in vitro, we demonstrate that synergid cell death initiates after the pollen tube arrives at the female gametophyte but before pollen tube discharge. Our results support a model in which a signaling cascade triggered by pollen tube-synergid cell contact induces synergid cell death in Arabidopsis. © 2007 American Society of Plant Biologists.
• Palanivelu, R., & Preuss, D. (2006). Distinct short-range ovule signals attract or repel Arabidopsis thaliana pollen tubes in vitro. BMC Plant Biology, 6.
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  PMID: 16595022;PMCID: PMC1489931;Abstract: Background: Pollen tubes deliver sperm after navigating through flower tissues in response to attractive and repulsive cues. Genetic analyses in maize and Arabidopsis thaliana and cell ablation studies in Torenia fournieri have shown that the female gametophyte (the 7-celled haploid embryo sac within an ovule) and surrounding diploid tissues are essential for guiding pollen tubes to ovules. The variety and inaccessibility of these cells and tissues has made it challenging to characterize the sources of guidance signals and the dynamic responses they elicit in the pollen tubes. Results: Here we developed an in vitro assay to study pollen tube guidance to excised A. thaliana ovules. Using this assay we discerned the temporal and spatial regulation and species-specificity of late stage guidance signals and characterized the dynamics of pollen tube responses. We established that unfertilized A. thaliana ovules emit diffusible, developmentally regulated, species-specific attractants, and demonstrated that ovules penetrated by pollen tubes rapidly release diffusible pollen tube repellents. Conclusion: These results demonstrate that in vitro pollen tube guidance to excised A. thaliana ovules efficiently recapitulates much of in vivo pollen tube behaviour during the final stages of pollen tube growth. This assay will aid in confirming the roles of candidate guidance molecules, exploring the phenotypes of A. thaliana pollen tube guidance mutants and characterizing interspecies pollination interactions. © 2006 Palanivelu and Preuss; licensee BioMed Central Ltd.
• Vigh, K. A., Preuss, D., Palanivelu, R., & Cummings, M. C. (2006). Phenotyping Allergen Sensitization Using Protein Arrays. The Journal of Allergy and Clinical Immunology, 117(2), S76. doi:10.1016/j.jaci.2005.12.304
• Palanivelu, R., Brass, L., Edlund, A. F., & Preuss, D. (2003). Pollen tube growth and guidance is regulated by POP2, an Arabidopsis gene that controls GABA levels. Cell, 114(1), 47-59.
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  PMID: 12859897;Abstract: During angiosperm reproduction, pollen grains form a tube that navigates through female tissues to the micropyle, delivering sperm to the egg; the signals that mediate this process are poorly understood. Here, we describe a role for γ-amino butyric acid (GABA) in pollen tube growth and guidance. In vitro, GABA stimulates pollen tube growth, although vast excesses are inhibitory. The Arabidopsis POP2 gene encodes a transaminase that degrades GABA and contributes to the formation of a gradient leading up to the micropyle. pop2 flowers accumulate GABA, and the growth of many pop2 pollen tubes is arrested, consistent with their in vitro GABA hypersensitivity. Some pop2 tubes continue to grow toward ovules, yet they are misguided, presumably because they target ectopic GABA on the ovule surface. Interestingly, wild-type tubes exhibit normal growth and guidance in pop2 pistils, perhaps by degrading excess GABA and sharpening the gradient leading to the micropyle.
• Palanivelu, R., & Preuss, D. (2000). Pollen tube targeting and axon guidance: Parallels in tip growth mechanisms. Trends in Cell Biology, 10(12), 517-524.
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  PMID: 11121743;Abstract: The growth of pollen tubes to plant egg cells and the guidance of axons to neural synapses are classic examples of targeted cell growth. Despite the evolutionary time that separates animals and plants, axon and pollen tube guidance share remarkable mechanistic similarities. In both instances, extracellular cues are transduced by intracellular signal-transduction pathways that culminate in directed tip growth. Do the mechanistic similarities extend to the molecular level? Here, we address this question by a comprehensive review of the molecules and pathways involved in pollen tube targeting and axon guidance. The emerging scenario is that similar intracellular molecules are recruited to control tip growth, while different extracellular molecules mediate guidance through the distinct plant and animal extracellular matrices. Copyright (C) 2000 Elsevier Science Ltd.
• Palanivelu, R., Belostotsky, D. A., & Meagher, R. B. (2000). Arabidopsis thaliana poly (A) binding protein 2 (PAB2) functions in yeast translational and mRNA decay processes. Plant Journal, 22(3), 187-198.
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  PMID: 10849337;Abstract: The single yeast gene (PAB1) encoding poly (A) binding protein (PABP) has several roles in post-transcriptional processes, including translation initiation and mRNA decay. PABP is encoded by a large gene family in plants. Within Arabidopsis thaliana, the several characterized PABP genes exhibit an extreme degree of sequence divergence and are differentially expressed. Arabidopsis PAB2 is expressed in distinct tissues or during defined developmental windows in most plant organs. In this study we demonstrate that PAB2 restores viability to a yeast pab1 mutant strain. Yeast strains containing wild-type, null (PAB2(s)) and temperature sensitive (PAB2(ts)) alleles of PAB2 were used to explore the molecular functions of the plant protein. PAB2 can participate in poly (A) tail shortening, thus demonstrating that it interacts with the yeast poly(A) nuclease complex. PAB2 is required for translation, helping to maintain intact polysome structures. Consistent with its role in translation initiation, poly (A) was found to enhance PAB2 binding to Arabidopsis eIF-iso4G in vitro. In addition, PAB2 can partially restore the linkage between deadenylation, decapping and mRNA decay in yeast. Taken together, our results suggest that Arabidopsis PAB2 participates in many of the same complex post-transcriptional processes identified for yeast PAB1, and is functionally distinct from other characterized Arabidopsis PABPs.
• Palanivelu, R., Belostotsky, D. A., & Meagher, R. B. (2000). Conserved expression of Arabidopsis thaliana poly (A) binding protein 2 (PAB2) in distinct vegetative and reproductive tissues. Plant Journal, 22(3), 199-210.
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  PMID: 10849338;Abstract: The poly(A) tails of eukaryotic mRNAs are complexed with poly(A) binding protein (PABP). The poly(A)-PABP complex is central to the efficient translation initiation and control of poly (A) tail length and is required in some pathways of mRNA decay. A large gene family encodes PABPs in Arabidopsis thaliana. In striking contrast to the floral and root specific expression of three previously reported Arabidopsis PABPs, we demonstrate that RNA and protein for one highly diverse member of this family, PAB2, are expressed in roots, stems, leaves, flowers, pollen and siliques of Arabidopsis. However, cell-type specific analysis of a PAB2 reporter gene fusion revealed that PAB2 is spatially and temporally regulated in each organ. For example, strong expression was detected only in the stele and meristem region of roots and a dramatic decrease in expression was observed upon fertilization of ovules. Furthermore, the PAB2-reporter construct gave a nearly identical expression pattern in transgenic tobacco, demonstrating that PAB2 expression is under strong selective constraint. The PAB2-reporter was also strongly expressed in the transmittal tissues of both Arabidopsis and tobacco, raising the possibility of its involvement in the pollination-dependent poly(A) tail shortening of transmittal tissue specific mRNAs previously reported in tobacco (Wang et al., 1996, Plant J. 9, 715-727). In view of its potential role in poly(A) tail shortening, we demonstrated the strong and distinct presence of PAB2 protein in transmittal tissues of Arabidopsis. The evolutionary and functional implications of the expression pattern of PAB2 and its possible functional roles in post-transcriptional regulation in transmittal tissues are discussed.

Proceedings Publications

• Simek, K., Palanivelu, R., & Barnard, K. (2016). Branching Gaussian Processes with Applications to Spatiotemporal Reconstruction of 3D Trees. In European Conference on Computer Vision, 9912, 177-193.
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  We propose a robust method for estimating dynamic 3D curvilinear branching structure from monocular images. While 3D reconstruction from images has been widely studied, estimating thin structure has received less attention. This problem becomes more challenging in the presence of camera error, scene motion, and a constraint that curves are attached in a branching structure. We propose a new general-purpose prior, a branching Gaussian processes (BGP), that models spatial smoothness and temporal dynamics of curves while enforcing attachment between them. We apply this prior to fit 3D trees directly to image data, using an efficient scheme for approximate inference based on expectation propagation. The BGP prior’s Gaussian form allows us to approximately marginalize over 3D trees with a given model structure, enabling principled comparison between tree models with varying complexity. We test our approach on a novel multi-view dataset depicting plants with known 3D structures and topologies undergoing small nonrigid motion. Our method outperforms a state-of-the-art 3D reconstruction method designed for non-moving thin structure. We evaluate under several common measures, and we propose a new measure for reconstructions of branching multi-part 3D scenes under motion.
• Zohar, Y., Zohar, Y., Qin, Y., Palanivelu, R., Jiang, L., & Cooper, J. R. (2009). Microsystem-Based Study of Pollen-Tube Attractants Secreted by Ovules. In 2009 IEEE 22nd International Conference on Micro Electro Mechanical Systems, 208-211.
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  Microdevices are developed to resemble the in-vivo micro-environment of ovule fertilization by pollen tubes in model research plant Arabidopsis thaliana. The PDMS-based microdevices are filled with pollen germination medium (PGM) providing pollen tubes with a proper growth environment. Pollen tubes are found to grow within the microgrooves with an average rate of 130?m/hr, reaching a final tube length of about 450?m. Targeting ovules by pollen tubes has also been tested with an observed efficiency of about 67%. Both the pollen tube growth rate and the ovule targeting efficiency in microdevices are similar to those obtained using in-vitro plate experiments. Finally, initial results indicate that pollen tube bundles preferentially turn toward ovule containing chambers, suggesting that the pollen tubes respond to the attractants secreted by unfertilized ovules.

Presentations

• Palanivelu, R. (2021, August). Pollen tube growth: critical link in stress tolerance and evolution of angiosperm reproduction. Research seminar at the McGill University. Seminar presentation via Zoom (due to COVID19): Department of Plant Sciences, McGill University.
• Palanivelu, R. (2021, November). Pollen tube growth: critical link in stress tolerance and evolution of angiosperm reproduction. Research Seminar at the University of Toronto. Seminar presentation via Zoom (due to COVID19): Department of Cell and Systems Biology, University of Toronto.
• Palanivelu, R. (2019, August). LORELEI and its most closely related paralog, LLG1, show evidence of regulatory subfunctionalization in Brassicaceae. Plant Biology 2019. San Jose, CA: American Society of Plant Biologists (ASPB).
• Palanivelu, R. (2019, February). Pollen: Nothing to Sneeze At!. CEAC seminar series. Tucson, AZ: CEAC.
• Palanivelu, R. (2019, June). Changes in gene expression underlie the diversification of the LORELEI gene family in Brassicaceae. Biology Seminar Series. Chennai, India: Indian Institute of Technology (IIT).
• Palanivelu, R. (2019, June). Changes in gene expression underlie the diversification of the LORELEI gene family in Brassicaceae. Institute Biology seminar series. Bangalore, India: Indian Institute of Science (IISC).
• Palanivelu, R. (2019, October). Evolutionary and Functional Analysis of a Multifunctional Plant Cell Signaling Complex. Plant Biology Seminar Series. East Lansing, MI: Department of Plant Biology, Michigan State University.
• Palanivelu, R. (2018, February). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Plant Biology Seminar Series, Department of Biochemistry and Molecular Biology. Amherst, Massachusetts: University of Massachusetts, Amherst.
• Palanivelu, R. (2018, September). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Department Seminar Series, Department of Molecular, Cellular, & Developmental Biology. Ann Arbor, Michigan: University of Michigan.
• Palanivelu, R. (2017, June). Arabidopsis LORELEI mediates female gametophyte control of pollen tube reception and early seed development. International Council of Arabidopsis Research. St. Louis, MO: International Council of Arabidopsis Research.
• Palanivelu, R. (2017, March). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Biology Department Seminar Series, University of Nevada, Reno. Reno, Nevada: University of Nevada.
• Palanivelu, R. (2017, November). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Department Seminar Series, Fudan University, Shanghai, China. Shanghai, China: Fudan University.
• Palanivelu, R. (2017, October). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Department Seminar Series, Fujian Agriculture and Forestry University, Fuzhou, China. Fuzhou, China: Fujian Agriculture and Forestry University.
• Palanivelu, R. (2017, October). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Department Seminar Series, Peking University. Beijing, China: Peking University.
• Palanivelu, R. (2017, September). Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Workshop on Molecular Mechanisms Controlling Flower Development. Padua, Italy: Workshop flower development 2017.
• Palanivelu, R. (2017, September). Closing the deal: Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Institute of Experimental Botany ASCR, Prague, Czech Republic. Prague, Czech Republic: Institute of Experimental Botany ASCR.
• Palanivelu, R. (2016, July). The Role of LORELEI in Pollen Tube Reception at the Interface of the Synergid Cell and Pollen Tube Requires the Receptor-Like Kinase FERONIA. Plant Biology 2016. Austin, Texas: American Society of Plant Biologists.
• Palanivelu, R. (2016, March). Arabidopsis LORELEI is a GPI-anchored membrane protein. "From sex to seed: a molecular dialogue"; 1st SEXSEED workshop. Tucson, Arizona: European Commission Horizon 2020.
• Palanivelu, R. (2016, October). Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Biology Department Seminar Series. Milwaukee, Wisconsin: UW, Milwaukee.
• Palanivelu, R. (2016, September). Arabidopsis LORELEI is required for pollen tube reception by the female gametophyte. Plant and Microbial Biology Department Seminar Series. Berkeley, California: UC Berkeley.
• Palanivelu, R. (2015, April). Molecular Genetic Analysis of LORELEI function in pollen tube reception in the Arabidopsis female gametophyte. Center for Plant Cell Biology, Department of Botany & Plant Sciences, University of California, Riverside. Riverside, California: University of California, Riverside.
• Palanivelu, R. (2015, April). Molecular Genetic Analysis of LORELEI function in pollen tube reception in the Arabidopsis female gametophyte. University of California, Berkeley and Plant Gene Expression Center. Albany, California: University of California, Berkeley and Plant Gene Expression Center.
• Palanivelu, R. (2015, August). Molecular Genetic Analysis of Pollen Tube Reception in Arabdiopsis. Overview of projects in the lab to the incoming freshman of the ABBS program. University of Arizona: Arizona Biological and Biomedical Sciences (ABBS).
• Palanivelu, R. (2015, February). Pollen: Nothing To Sneeze At!. Monthly meeting of Life Sciences Student Association, University of Arizona. University of Arizona: Life Science Student Association.
• Palanivelu, R. (2015, January). Molecular Genetic Analysis of Pollen Tube Reception in Arabdiopsis. School of Plant Sciences Research Retreat. Tucson, Arizona: School of Plant Sciences.
• Palanivelu, R. (2015, January). Molecular Genetic Analysis of Pollen Tube Reception in Arabdiopsis. School of Plant Sciences Seminar - Research Overview talks. University of Arizona: School of Plant Sciences.
• Palanivelu, R. (2015, July). Molecular Genetic Analysis of LORELEI function in pollen tube reception in the Arabidopsis female gametophyte. International Council of Arabidopsis Research Annual Meeting. Paris, France: International Council of Arabidopsis Research.
• Palanivelu, R. (2015, July). Pollen tube discharge completes the process of synergid degeneration that is initiated by pollen tube – synergid interaction in Arabidopsis. 5th Annual meeting of Pollen Research Coordination Network. University of Minnesota, Minneapolis: Pollen RCN.
• Palanivelu, R. (2015, October). Molecular genetic analysis of LORELEI function in mediating interactions between the Arabidopsis female gametophyte and the pollen tube. PBS Colloquium Seminar Series, University of Minnesota. Minneapolis: University of Minnesota, Minneapolis.
• Palanivelu, R., Castro, C., Wang, Y., Noble, J., & Liu, X. (2015, July). Molecular Genetic Analysis of LORELEI function in pollen tube reception in the Arabidopsis female gametophyte. 5th Annual meeting of Pollen Research Coordination Network. University of Minnesota, Minneapolis: Pollen RCN.
• Noble, J., Beilstein, M. A., & Palanivelu, R. (2014, November). Is LORELEI, a Putative Glycosylphosphatidylinositol-Anchored Membrane Protein Involved in Pollen Tube Reception in Arabidopsis thaliana, Undergoing Selection?. 2014 SACNAS National Conference. Los Angeles, CA: SACNAS (Society for Advancing Hispanics, Chicanos, Native Americans in Science).
• Palanivelu, R. (2014, July). Molecular genetic analysis of LORELEI function in inducing the arrest of pollen tube growth in the Arabidopsis female gametophyte. Plant Biology 2014. Portland, OR: American Society of Plant Biologists.
• Palanivelu, R. (2014, May). Sulfinylated Azadecalins Act as Functional Mimics of a Pollen Germination Stimulant in Arabidopsis Pistils. Monsanto. Chesterfield, MO: Monsanto.
• Palanivelu, R. -. (2014, March). Sulfinylated Azadecalins Act as Functional Mimics of a Pollen Germination Stimulant in Arabidopsis Pistils. 2014 Arizona Mass Spectrometry Users Meeting. Keating Building, University of Arizona, Tucson, AZ: Arizona Mass Spectrometry User Meeting.
• Palanivelu, R., & Johnson, M. (2014, May). Caught in the act: Pollen-Pistil Transcriptomics. WiNGS 2014. Charlotte, NC: Pollen RCN.
• Palanivelu, R. -. (2013, July). Molecular genetic analysis of LORELEI function in Arabidopsis reproduction. Gordon Research Conference: Fertilization & Activation of Development, HoldernesS, NH. Holderness, New Hampshire: Gordon Research Conference.
• Palanivelu, R. -. (2013, March). An Arabidopsis mutant defective in pollen tube elongation. Third Annual Meeting of the Pollen Research Coordination Network, Tucson, AZ. Tucson, Arizona: Pollen RCN.
• Palanivelu, R. -. (2013, November). Molecular Genetic Analysis of Expression of Meiosis-related Genes in Arabidopsis. Department of Cell Biology and Molecular Genetics seminar series, University of Maryland, College Park. University of Maryland, College Park.
• Palanivelu, R. -. (2013, October). Molecular Genetic Analysis of Expression of Meiosis-related Genes in Arabidopsis. European Frontiers of Plant Reproduction Research 2013, Oslo, Norway. Oslo, Norway.
• Palanivelu, R. -. (2012, August). Molecular mechanisms underlying pollen-pistil interactions in Arabidopsis. Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences (Shanghai, China) seminar series. Shanghai, China.
• Palanivelu, R. -. (2012, August). Molecular mechanisms underlying pollen-pistil interactions in Arabidopsis. Tamilnadu Agriculture University (Coimbatore, India) seminar series. Coimbatore, India.
• Palanivelu, R. -. (2012, July). Molecular Mechanisms underlying pollen-pistil interactions in Arabidopsis. Center for Cellular and Molecular Biology (CCMB, Hyderabad, India) seminar series. Hyderabad, India.
• Palanivelu, R. -. (2012, November). Regulation of pollen tube guidance by the Arabidopsis female gametophyte.. International Symposium on the Mechanisms of Sexual Reproduction in Animals and Plants, Nagoya, Japan.
• Palanivelu, R. -. (2011, August). Molecular mechanisms of pollen-pistil interactions. New Graduate Student Orientation, Arizona Biological and Biomedical Sciences (ABBS) graduate program, University of Arizona. Tucson, Arizona.
• Palanivelu, R. -. (2011, Feburary). Molecular mechanisms underlying pollen-pistil interactions in Arabidopsis. Graduate Student Recruitment, Arizona Biological and Biomedical Sciences (ABBS) graduate program, University of Arizona. Tucson, Arizona.
• Palanivelu, R. -. (2011, January). Molecular Mechanisms underlying pollen-pistil interactions in Arabidopsis. Division of Molecular Biology and Biochemistry, University of Missouri, Kansas City seminar series.
• Palanivelu, R. -. (2011, March). Molecular Mechanisms underlying pollen-pistil interactions in Arabidopsis. Plant Biology Graduate Program, University of Massachusetts, Amherst seminar series.
• Palanivelu, R. -. (2011, March). Molecular Mechanisms underlying pollen-pistil interactions. Department of Molecular Biology, Cell Biology and Biochemistry, Brown University seminar series. Providence, Rhode Islan.
• Palanivelu, R. -. (2011, September). Molecular Mechanisms underlying pollen-pistil interactions in Arabidopsis. School of Plant Sciences seminar series. Tucson, Arizona.

Poster Presentations

• Cheung, A., Feijo, J., Johnson, M., & Palanivelu, R. (2018, June). Research Coordination Network on Integrative Pollen Biology: Report and perspectives on fostering a community of pollen biology researchers. Plant Reproduction 2018. Gifu, Japan: International Association of Sexual Plant Reproduction Research.
• Desnoyer, N., Liu, X., & Palanivelu, R. (2018, June). Mutation in a glycosylphosphatidylinositol (GPI) transamidase complex subunit disrupts male gametophyte function in Arabidopsis. Plant Reproduction 2018. Gifu, Japan: International Association of Sexual Plant Reproduction Research.
• Noble, J., Beilstein, M., Cheung, A., & Palanivelu, R. (2018, July). LORELEI, and its most closely related paralog LLG1, have similar function but divergent expression patterns. Plant Biology 2018. Montreal, Canada: American Society of Plant Biologists.
• Wang, Y., Tsukamoto, T., Noble, J., Mosher, R. A., & Palanivelu, R. (2017, June). Arabidopsis Lorelei, a maternally-expressed imprinted gene, promotes early Seed Development. Plant Biology 2017. Honolulu, Hawaii: International Association of Sexual Plant Reproduction.
  More info

  The poster was selected for a talk and Jen Noble, my graduate student gave an oral presentation.
• Dixon, J., Palanivelu, R., Cheung, A., & Owens, H. (2016, March). Ultrastructural analysis of Arabidopsis thaliana ovules. Plant Reproduction 2016. Tucson, Arizona: International Association of Sexual Plant Reproduction.
• Liu, X., Castro, C., Wang, Y., Noble, J., Ponvert, N., Bundy, M., Hoel, C., Shpak, E., & Palanivelu, R. (2016, March). LORELEI Function in Pollen Tube Reception at the Interface of the Synergid Cell and the Pollen Tube Requires the Modified Eight-Cysteine Motif and FERONIA Receptor-Like Kinase. Plant Reproduction 2016. Tucson, Arizona: International Association of Sexual Plant Reproduction.
• Noble, J., Beilstein, M. A., & Palanivelu, R. (2016, March). Evolutionary and Functional Analysis of LORELEI, a GPI-Anchored Membrane Protein Involved in Pollen Tube Reception in Arabidopsis thaliana. Plant Reproduction 2016. Tucson, Arizona: International Association of Sexual Plant Reproduction.
• Wang, Y., Tsukamoto, T., Liu, X., Noble, J., Harris, R. A., & Palanivelu, R. (2016, March). A growth-promoting role for LORELEI, a maternally expressed imprinted gene, in early seed development in Arabidopsis. Plant Reproduction 2016. Tucson, Arizona: International Association of Sexual Plant Reproduction.
• Liu, X., Castro, C., Hoel, C., Wang, Y., & Palanivelu, R. (2015, January). Localization of LORELEI, a putative glycosylphosphatidylinositol (GPI)-anchored membrane protein, in the Arabidopsis female gametophyte. School of Plant Sciences Research Retreat. Tucson, Arizona: School of Plant Sciences.
• Wang, Y., Tsukamoto, T., Liu, X., Noble, J., Harris, R. A., & Palanivelu, R. (2015, January). A growth-promoting role for Arabidopsis LORELEI, a maternally expressed imprinted gene, in early seed development. School of Plant Sciences Research Retreat. Tucson, Arizona: School of Plant Sciences.
• Wang, Y., Tsukamoto, T., Liu, X., Noble, J., Harris, R. A., & Palanivelu, R. (2015, July). A growth-promoting role for Arabidopsis LORELEI, a maternally expressed imprinted gene, in early seed development. 5th Annual meeting of Pollen Research Coordination Network. University of Minneapolis, Minnesota: Pollen RCN.
• Castro, C., Liu, X., & Palanivelu, R. (2014, August). Subcellular localization of LORELEI protein in Arabidopsis thaliana reproduction. Summer Research Institute, UROC-University of Arizona. University of Arizona, Tucson, AZ: Student Affairs Research Program.
  More info

  Claudia Castro, a minority student, was selected to participate in the Summer Research Institute as part of Student Affairs Research Program. The Summer Research Institute (SRI) offers students like Claudia an outstanding opportunity to learn how to conduct research and prepare for graduate studies at The University of Arizona (UA) or other Universities in the nation. At the end of the program, Claudia presented an oral and a poster presentations on the research she did in my lab.
• Castro, C., Liu, X., & Palanivelu, R. (2014, November). Subcellular localization of LORELEI protein in Arabidopsis thaliana reproduction. 2014 SACNAS National Conference. Los Angeles, CA: Society for Advancing Hispanics, Chicanos, and Native Americans in Science.
• Liu, X., Castro, C., Hoel, C., Wang, Y., & Palanivelu, R. (2014, July). Localization of LORELEI, a putative glycosylphosphatidylinositol (GPI)-anchored membrane protein, in the Arabidopsis female gametophyte. ICAR 2014. Vancouver, BC, Canada: International Council of Arabidopsis Research.
• Liu, X., Castro, C., Hoel, C., Wang, Y., & Palanivelu, R. (2014, July). Localization of LORELEI, a putative glycosylphosphatidylinositol (GPI)-anchored membrane protein, in the Arabidopsis female gametophyte. Plant Biology 2014. Portland, OR: American Society of Plant Biologists.
• Noble, J., Beilstein, M. A., & Palanivelu, R. (2014, July). Is LORELEI, a Putative Glycosylphosphatidylinositol-Anchored Membrane Protein Involved in Pollen Tube Reception in Arabidopsis thaliana, Undergoing Selection?. Plant Biology 2014. Portland, OR: American Society of Plant Biologists.
  More info

  Poster Presentation
• Palanivelu, R., Beilstein, M. A., & Noble, J. (2014, April). Is LORELEI, a Putative Glycosylphosphatidylinositol-Anchored Membrane Protein Involved in Pollen Tube Reception in Arabidopsis thaliana, Undergoing Selection?. Deep Genomics Symposium. Tucson, AZ: UA IGERT program in comparative genomics.
  More info

  Authors: Jennifer Noble, Mark Beilstein, and Ravishankar Palanivelu

Others

• Zhao, D., Chong, K., & Palanivelu, R. (2017, Feburary). Editorial: Molecular and Cellular Plant Reproduction. Frontiers In Plant Sciences. https://www.frontiersin.org/articles/10.3389/fpls.2017.00199/full
• Palanivelu, R. -. (2011, Fall). Reproduction and Development in Flowering Plants. Biology: The Dynamic Science.
  More info

  Essay on unanswered questions in the field of pollen tube growth and guidance, in Chapter 34, Reproduction and Development in Flowering Plants, p. 798 in Biology: The Dynamic Science, Peter Russell, Paul Hertz, and Beverly McMillan (2nd edition). United States: Brooks/Cole, Cengage Learning.