Karen S Schumaker
- Professor, Plant Sciences
- Professor, BIO5 Institute
- Ph.D. Botany and Plant Pathology
- University of Maryland, College Park, Maryland
- M.S. Agronomy, Plant Breeding and Genetics
- Oregon State University, Corvallis, Oregon
- University of Arizona, Tucson, Arizona (2013 - Ongoing)
- University of Arizona, Tucson, Arizona (2012 - 2014)
- University of Arizona, Tucson, Arizona (2011 - Ongoing)
- National Science Foundation, IOS (2003 - 2004)
- National Science Foundation, IOS (2001 - 2002)
- Graduate and Professional Education and Teaching and Mentoring Award
- University of Arizona, Office of the Provost, Spring 2012
Plant Development/ Current Topics in Plant Biology
Understanding how gene duplication contributes to plant adaptation/ Identifying determinants and pathways that regulate plant responses to soil salinity
Advanced Plant BiologyPLS 560 (Fall 2020)
Advanced Plant BiologyPLS 560 (Fall 2019)
Senior CapstoneBIOC 498 (Spring 2018)
Senior CapstoneBIOC 498 (Fall 2017)
Directed RsrchMCB 492 (Spring 2016)
Senior CapstoneBIOC 498 (Spring 2016)
- Schumaker, K. S., Monihan, S. M., Ryu, C., & Magness, C. A. (2019). Linking Duplication of a Calcium Sensor to Salt Tolerance in Eutrema salsugineum. Plant Physiology, 179, 1176-1192.
- Schumaker, K. S., Yadegari, R., Drews, G., Zhang, S., Wang, D., Zhang, H., Skaggs, M. I., Lloyd, A., & An, L. (2018). FERTILIZATION-INDEPENDENT SEED-Polycomb Repressive Complex 2 plays a dual role in regulating Type I MADS-Box genes in early endosperm development. Plant Physiology, 177, 285-299. doi:DOI: https://doi.org/10.1104/pp.17.00534
- Monihan, S. M., Magness, C. A., Yadegari, R., Smith, S. E., & Schumaker, K. S. (2016). Arabidopsis CALCINEURIN B-LIKE10 functions independently of the SOS pathway during reproductive development in saline conditions. Plant Physiology, 171, 369-379.
- Li, J., Liu, J., Wang, G., Cha, J., Li, G., Chen, S., Li, Z., Guo, J., Zhang, C., Yang, Y., Kim, W., Yun, D., Schumaker, K. S., Chen, Z., & Guo, Y. (2015). A Chaperone Function of NO CATALASE ACTIVITY1 Is Required to Maintain Catalase Activity and for Multiple Stress Responses in Arabidopsis. PLANT CELL, 27(3), 908-925.
- Zhou, X., Hao, H., Zhang, Y., Bai, Y., Zhu, W., Qin, Y., Yuan, F., Zhao, F., Wang, M., Hu, J., Xu, H., Guo, A., Zhao, H., Zhao, Y., Cao, C., Yang, Y., Schumaker, K. S., Guo, Y., & Xie, C. G. (2015). SOS2-LIKE PROTEIN KINASE5, an SNF1-RELATED PROTEIN KINASE3-Type Protein Kinase, Is Important for Abscisic Acid Responses in Arabidopsis through Phosphorylation of ABSCISIC ACID-INSENSITIVE5. PLANT PHYSIOLOGY, 168(2), 659-+.
- Jarvis, D. E., Ryu, C., Beilstein, M. A., & Schumaker, K. S. (2014). Distinct roles of SOS1 in the convergent evolution of salt tolerance in Eutrema salsugineum and Schrenkiella parvula. Molecular Biology and Evolution.
- Schumaker, K. S., & Guo, Y. (2014). A Calcium-Independent Activation of the Arabidopsis SOS2-Like Protein Kinase24 by Its Interacting SOS3-Like Calcium Binding Protein1. Plant Physiology, 164, 2197-2206.
- Schumaker, K. S., & Guo, Y. (2014). Inhibition of the Arabidopsis Salt Overly Sensitive Pathway by 14-3-3 Proteins. Plant Cell, 26, 1166-1182.
- Schumaker, K. S. (2013). An atlas of over 90,000 conserved noncoding sequences provides insight into crucifer regulatory regions. Nature Genetics, 45, 891–898.More infoProvides sequencing of genomes from three Brassicaceae species (Leavenworthia alabamica, Sisymbrium irio and Aethionema arabicum) and their joint analysis with six previously sequenced crucifer genomes. Conservation across orthologous bases suggests that at least 17% of the Arabidopsis thaliana genome is under selection, with nearly one-quarter of the sequence under selection lying outside of coding regions. Much of this sequence can be localized to approximately 90,000 conserved noncoding sequences (CNSs) that show evidence of transcriptional and post-transcriptional regulation. Population genomics analyses of two crucifer species, A. thaliana and Capsella grandiflora, confirm that most of the identified CNSs are evolving under medium to strong purifying selection.
- Schumaker, K. S. (2013). The Actin-Related Protein2/3 Complex Regulates Mitochondrial-Associated Calcium Signaling during Salt Stress in Arabidopsis. Plant Cell, 25, 4544-4559.
- Schumaker, K. S. (2013). The reference genome of the halophytic plant Eutrema salsugineum. Frontiers in Plant Science, 1-14.More infoPresents the reference genome sequence (241 Mb) of E. salsugineum at 8× coverage sequenced using the traditional Sanger sequencing-based approach with comparison to its close relative Arabidopsis thaliana.
- Zhou, H., Zhao, J., Yang, Y., Chen, C., Liu, Y., Jin, X., Chen, L., Xueyong, L. i., Deng, X. W., Schumaker, K. S., & Guo, Y. (2013). UBIQUITIN-SPECIFIC PROTEASE16 modulates salt tolerance in arabidopsis by regulating Na+/H+ antiport activity and serine hydroxymethyltransferase stability. Plant Cell, 24(12), 5106-5122.More infoPMID: 23232097;PMCID: PMC3556978;Abstract: Protein ubiquitination is a reversible process catalyzed by ubiquitin ligases and ubiquitin-specific proteases (UBPs). We report the identification and characterization of UBP16 in Arabidopsis thaliana. UBP16 is a functional ubiquitin-specific protease and its enzyme activity is required for salt tolerance. Plants lacking UBP16 were hypersensitive to salt stress and accumulated more sodium and less potassium. UBP16 positively regulated plasma membrane Na+/H+ antiport activity. Through yeast two-hybrid screening, we identified a putative target of UBP16, SERINE HYDROXYMETHYLTRANSFERASE1 (SHM1), which has previously been reported to be involved in photorespiration and salt tolerance in Arabidopsis. We found that SHM1 is degraded in a 26S proteasome-dependent process, and UBP16 stabilizes SHM1 by removing the conjugated ubiquitin. Ser hydroxymethyltransferase activity is lower in the ubp16 mutant than in the wild type but higher than in the shm1 mutant. During salt stress, UBP16 and SHM1 function in preventing cell death and reducing reactive oxygen species accumulation, activities that are correlated with increasing Na+/H+ antiport activity. Overexpression of SHM1 in the ubp16 mutant partially rescues its salt-sensitive phenotype. Taken together, our results suggest that UBP16 is involved in salt tolerance in Arabidopsis by modulating sodium transport activity and repressing cell death at least partially through modulating SMH1stability and activity. © 2012 American Society of Plant Biologists.
- Zheng, Y., Schumaker, K., & Guo, Y. (2012). Sumoylation of transcription factor MYB30 by the small ubiquitin-like modifier E3 ligase SIZ1 mediates abscisic acid response in Arabidopsis thaliana. Proceedings of the National Academy of Sciences, 109, 12822-12827.
- Drews, G., Wang, D., Steffen, J., Schumaker, K., & Yadegari, R. (2011). Identification of genes expressed in the Angiosperm female gametophyte. J. Exp. Bot, 62, 1593-1599.
- Wang, D., Zhang, C., Hearn, D. J., Kang, I., Punwani, J. A., Skaggs, M. I., Drews, G. N., Schumaker, K. S., & Yadegari, R. (2010). Identification of transcription-factor genes expressed in the Arabidopsis female gametophyte. BMC Plant Biology, 10.More infoPMID: 20550711;PMCID: PMC3236301;Abstract: Background: In flowering plants, the female gametophyte is typically a seven-celled structure with four cell types: the egg cell, the central cell, the synergid cells, and the antipodal cells. These cells perform essential functions required for double fertilization and early seed development. Differentiation of these distinct cell types likely involves coordinated changes in gene expression regulated by transcription factors. Therefore, understanding female gametophyte cell differentiation and function will require dissection of the gene regulatory networks operating in each of the cell types. These efforts have been hampered because few transcription factor genes expressed in the female gametophyte have been identified. To identify such genes, we undertook a large-scale differential expression screen followed by promoter-fusion analysis to detect transcription-factor genes transcribed in the Arabidopsis female gametophyte.Results: Using quantitative reverse-transcriptase PCR, we analyzed 1,482 Arabidopsis transcription-factor genes and identified 26 genes exhibiting reduced mRNA levels in determinate infertile 1 mutant ovaries, which lack female gametophytes, relative to ovaries containing female gametophytes. Spatial patterns of gene transcription within the mature female gametophyte were identified for 17 transcription-factor genes using promoter-fusion analysis. Of these, ten genes were predominantly expressed in a single cell type of the female gametophyte including the egg cell, central cell and the antipodal cells whereas the remaining seven genes were expressed in two or more cell types. After fertilization, 12 genes were transcriptionally active in the developing embryo and/or endosperm.Conclusions: We have shown that our quantitative reverse-transcriptase PCR differential-expression screen is sufficiently sensitive to detect transcription-factor genes transcribed in the female gametophyte. Most of the genes identified in this study have not been reported previously as being expressed in the female gametophyte. Therefore, they might represent novel regulators and provide entry points for reverse genetic and molecular approaches to uncover the gene regulatory networks underlying female gametophyte development. © 2010 Wang et al; licensee BioMed Central Ltd.
- Yang, Y., Qin, Y., Xie, C., Zhao, F., Zhao, J., Liu, D., Chen, S., Fuglsang, A. T., Palmgren, M. G., Schumaker, K. S., Deng, X. W., & Guo, Y. (2010). The Arabidopsis chaperone J3 regulates the plasma membrane H+-ATPase through interaction with the PKS5 kinase. Plant Cell, 22(4), 1313-1332.More infoPMID: 20418496;PMCID: PMC2879748;Abstract: The plasma membrane H+-ATPase (PM H+-ATPase) plays an important role in the regulation of ion and metabolite transport and is involved in physiological processes that include cell growth, intracellular pH, and stomatal regulation. PM H+-ATPase activity is controlled by many factors, including hormones, calcium, light, and environmental stresses like increased soil salinity. We have previously shown that the Arabidopsis thaliana Salt Overly Sensitive2-Like Protein Kinase5 (PKS5) negatively regulates the PM H+-ATPase. Here, we report that a chaperone, J3 (DnaJ homolog 3; heat shock protein 40-like), activates PM H+-ATPase activity by physically interacting with and repressing PKS5 kinase activity. Plants lacking J3 are hypersensitive to salt at high external pH and exhibit decreased PM H+-ATPase activity. J3 functions upstream of PKS5 as double mutants generated using j3-1 and several pks5 mutant alleles with altered kinase activity have levels of PM H+-ATPase activity and responses to salt at alkaline pH similar to their corresponding pks5 mutant. Taken together, our results demonstrate that regulation of PM H+-ATPase activity by J3 takes place via inactivation of the PKS5 kinase. © 2010 American Society of Plant Biologists.
- Zhang, C., Guo, H., Zhang, J., Guo, G., Schumaker, K. S., & Guob, Y. (2010). Arabidopsis cockayne syndrome a-like proteins 1A and 1B form a complex with CULLIN4 and damage DNA binding protein 1A and regulate the response to UV irradiation. Plant Cell, 22(7), 2353-2369.More infoPMID: 20622147;PMCID: PMC2929103;Abstract: In plants, as in animals, DNA is constantly subject to chemical modification. UV-B irradiation is a major genotoxic agent and has significant effects on plant growth and development. Through forward genetic screening, we identified a UV-B- sensitive mutant (csaat1a-3) in Arabidopsis thaliana, in which expression of CSAat1A, encoding a Cockayne Syndrome A-like protein, is reduced due to insertion of a T-DNA in the promoter region. Arabidopsis lacking CSAat1A or its homolog CSAat1B is more sensitive to UV-B and the genotoxic drug methyl methanesulfonate and exhibits reduced transcriptioncoupled repair activity. Yeast two-hybrid analysis indicated that both CSAat1A and B interact with DDB1A (UV-Damage DNA Binding Protein1). Coimmunoprecipitation assays demonstrated that CSAat1A and B associate with the CULLIN4 (CUL4)- DDB1A complex in Arabidopsis. A split-yellow fluorescent protein assay showed that this interaction occurs in the nucleus, consistent with the idea that the CUL4-DDB1A-CSA complex functions as a nuclear E3 ubiquitin ligase. CSAat1A and B formed heterotetramers in Arabidopsis. Taken together, our data suggest that the plant CUL4-DDB1ACSAat1A and B complex represents a unique mechanism to promote ubiquitination of substrates in response to DNA damage. © 2010 American Society of Plant Biologists.
- Lin, H., Yang, Y., Quan, R., Mendoza, I., Yisheng, W. u., Wenming, D. u., Zhao, S., Schumaker, K. S., Pardo, J. M., & Guo, Y. (2009). Phosphorylation of SOS3-like calcium binding protein8 by SOS2 protein kinase stabilizes their protein complex and regulates salt tolerance in arabidopsis. Plant Cell, 21(5), 1607-1619.More infoPMID: 19448033;PMCID: PMC2700523;Abstract: The Salt Overly Sensitive (SOS) pathway plays an important role in the regulation of Na +/K + ion homeostasis and salt tolerance in Arabidopsis thaliana. Previously, we reported that the calcium binding proteins SOS3 and SOS3-LIKE CALCIUM BINDING PROTEIN8 (SCaBP8) nonredundantly activate the protein kinase SOS2. Here, we show that SOS2 phosphorylates SCaBP8 at its C terminus but does not phosphorylate SOS3. In vitro, SOS2 phosphorylation of SCaBP8 was enhanced by the bimolecular interaction of SOS2 and SCaBP8 and did not require calcium ions. In vivo, this phosphorylation was induced bysalt stress, occurred at the membrane, stabilized the SCaBP8-SOS2 interaction, and enhanced plasma membrane Na +/H + exchange activity. When a Ser at position 237 in the SCaBP8 protein (the SOS2 phosphorylation target) was mutated to Ala, SCaBP8 was no longer phosphorylated by SOS2 and the mutant protein could not fully rescue the salt-sensitive phenotype of the scabp8 mutant. By co ntrast, when Ser-237 was mutated to Asp to mimic the charge of a phosphorylated Ser residue, the mutant protein rescued the scabp8 salt sensitivity. These data demonstrate that calcium sensor phosphorylation is a critical component of SOS pathway regulation of salt tolerance in Arabidopsis. © 2009 American Society of Plant Biologists.
- Schumaker, K., Nah, G., Pagliarulo, C. L., Mohr, P. G., Luo, M., Sisneros, N., Yu, Y., Collura, K., Currie, J., Goicoechea, J. L., Wing, R. A., & Schumaker, K. S. (2009). Comparative sequence analysis of the SALT OVERLY SENSITIVE1 orthologous region in Thellungiella halophila and Arabidopsis thaliana. Genomics, 94(3).More infoTo provide a framework for studies to understand the contribution of SALT OVERLY SENSITIVE1 (SOS1) to salt tolerance in Thellungiella halophila, we sequenced and annotated a 193-kb T. halophila BAC containing a putative SOS1 locus (ThSOS1) and compared the sequence to the orthologous 146-kb region of the genome of its salt-sensitive relative, Arabidopsis thaliana. Overall, the two sequences were colinear, but three major expansion/contraction regions in T. halophila were found to contain five Long Terminal Repeat retrotransposons, MuDR DNA transposons and intergenic sequences that contribute to the 47.8-kb size variation in this region of the genome. Twenty-seven genes were annotated in the T. halophila BAC including the putative ThSOS1 locus. ThSOS1 shares gene structure and sequence with A. thaliana SOS1 including 11 predicted transmembrane domains and a cyclic nucleotide-binding domain; however, different patterns of Simple Sequence Repeats were found within a 540-bp region upstream of SOS1 in the two species.
- Gao, Y., Gong, X., Cao, W., Zhao, J., Liqin, F. u., Wang, X., Schumaker, K. S., & Guo, Y. (2008). SAD2 in arabidopsis functions in trichome initiation through mediating GL3 function and regulating GL1, TTG1 and GL2 expression. Journal of Integrative Plant Biology, 50(7), 906-917.More infoPMID: 18713401;Abstract: Most genes identified that control Arabidopsis trichome initiation and formation are transcription factors or regulatory components in transcriptional networks and include GLABROUS1 (GL1), GLABRA2 (GL2), GLABRA3 (GL3) and TRANSPARENT TESTA GLABRA1 (TTG1). Herein, we report that an importin β-like protein, SENSITIVE TO ABA AND DROUGHT2 (SAD2), is required for trichome initiation. Mutations in SAD2 disrupted trichome initiation resulting in reduced trichome number, but had no effect on trichome development or root hair number and development. Expression levels of GL1, MYB23, GL2 and TTG1 were reduced in shoots of sad2 mutants while expression levels of GL3 and ENHANCER OF GLABRA3 (EGL3) were enhanced. Overexpression of GL3 increased trichome numbers in wild type but not in sad2 mutants, indicating that the function of the GL3 protein is altered in the sad2 mutants. In contrast, overexpression of GFP-GL1 decreased trichome number in both wild type and sad2. Double mutant analysis of gl1 sad2 and gl3 sad2 indicated that SAD2 functions genetically, at least in part, in the same pathway with these two genes. Co-immunoprecipitation indicated that the sad2 mutation does not disrupt formation of the TTG1-GL3-GL1 complex. Analysis of GFP fusions of GL1, GL2, GL3 and TTG1 suggested that these proteins are most likely not direct cargo of SAD2. Our data suggest that SAD2 is involved in trichome initiation by regulating these nuclear genes. © 2008 Institute of Botany, the Chinese Academy of Sciences.
- Batelli, G., Verslues, P. E., Agius, F., Qiu, Q., Fujii, H., Pan, S., Schumaker, K. S., Grillo, S., & Zhu, J. (2007). SOS2 promotes salt tolerance in part by interacting with the vacuolar H+-ATPase and upregulating its transport activity. Molecular and Cellular Biology, 27(22), 7781-7790.More infoPMID: 17875927;PMCID: PMC2169139;Abstract: The salt overly sensitive (SOS) pathway is critical for plant salt stress tolerance and has a key role in regulating ion transport under salt stress. To further investigate salt tolerance factors regulated by the SOS pathway, we expressed an N-terminal fusion of the improved tandem affinity purification tag to SOS2 (NTAP-SOS2) in sos2-2 mutant plants. Expression of NTAP-SOS2 rescued the salt tolerance defect of sos2-2 plants, indicating that the fusion protein was functional in vivo. Tandem affinity purification of NTAP-SOS2-containing protein complexes and subsequent liquid chromatography-tandem mass spectrometry analysis indicated that subunits A, B, C, E, and G of the peripheral cytoplasmic domain of the vacuolar H+-ATPase (V-ATPase) were present in a SOS2-containing protein complex. Parallel purification of samples from control and salt-stressed NTAP-SOS2/sos2-2 plants demonstrated that each of these V-ATPase subunits was more abundant in NTAP-SOS2 complexes isolated from salt-stressed plants, suggesting that the interaction may be enhanced by salt stress. Yeast two-hybrid analysis showed that SOS2 interacted directly with V-ATPase regulatory subunits B1 and B2. The importance of the SOS2 interaction with the V-ATPase was shown at the cellular level by reduced H+ transport activity of tonoplast vesicles isolated from sos2-2 cells relative to vesicles from wild-type cells. In addition, seedlings of the det3 mutant, which has reduced V-ATPase activity, were found to be severely salt sensitive. Our results suggest that regulation of V-ATPase activity is an additional key function of SOS2 in coordinating changes in ion transport during salt stress and in promoting salt tolerance. Copyright © 2007, American Society for Microbiology. All Rights Reserved.
- Fuglsang, A. T., Guo, Y., Cuin, T. A., Qiu, Q., Song, C., Kristiansen, K. A., Bych, K., Schulz, A., Shabala, S., Schumaker, K. S., Palmgren, M. G., & Zhub, J. (2007). Arabidopsis protein kinase PKS5 inhibits the plasma membrane H +-ATPase by preventing interaction with 14-3-3 protein. Plant Cell, 19(5), 1617-1634.More infoPMID: 17483306;PMCID: PMC1913743;Abstract: Regulation of the trans-plasma membrane pH gradient is an important part of plant responses to several hormonal and environmental cues, including auxin, blue light, and fungal elicitors. However, little is known about the signaling components that mediate this regulation. Here, we report that an Arabidopsis thaliana Ser/Thr protein kinase, PKS5, is a negative regulator of the plasma membrane proton pump (PM H+-ATPase). Loss-of-function pks5 mutant plants are more tolerant of high external pH due to extrusion of protons to the extracellular space. PKS5 phosphorylates the PM H+-ATPase AHA2 at a novel site, Ser-931, in the C-terminal regulatory domain. Phosphorylation at this site inhibits interaction between the PM H+-ATPase and an activating 14-3-3 protein in a yeast expression system. We show that PKS5 interacts with the calcium binding protein SCaBP1 and that high external pH can trigger an increase in the concentration of cytosolic-free calcium. These results suggest that PKS5 is part of a calcium-signaling pathway mediating PM H+-ATPase regulation. © 2007 American Society of Plant Biologists.
- Zhao, J., Zhang, W., Zhao, Y., Gong, X., Guo, L., Zhu, G., Wang, X., Gong, Z., Schumaker, K. S., & Guo, Y. (2007). SAD2, an importin β-like protein, is required for UV-B response in Arabidopsis by mediating MYB4 nuclear trafficking. Plant Cell, 19(11), 3805-3818.More infoPMID: 17993626;PMCID: PMC2174865;Abstract: We report that the Arabidopsis thaliana mutant sensitive to ABA and drought2 (sad2), which harbors a T-DNA insertion in an importin β-like gene, is more tolerant to UV-B radiation than the wild type. Analysis of cyclobutane pyrimidine dimer accumulation revealed that less DNA damage occurred in sad2 than in the wild type during UV-B treatment. No significant growth difference was observed between sad2 and the wild type when treated with the genotoxic drug methyl methanesulfonate, suggesting that SAD2 functions in UV-B protection rather than in DNA damage repair. Whereas the R2R3-type transcription repressor MYB4 has previously been shown to negatively regulate the transcription of cinnamate 4-hydroxylase (C4H) and thus to regulate the synthesis of sinapate esters, expression of both MYB4 and C4H and accumulation of UV-absorbing compounds were significantly higher in sad2 than in the wild type. MYB4 did not localize to the nucleus in the sad2 mutant, suggesting that SAD2 is required for MYB4 nuclear trafficking. SAD2 and MYB4 coimmunoprecipitated, indicating that these proteins localize in the same complex in vivo. MYB4 protein specifically bound to its own promoter in gel shift assays and repressed its own expression, demonstrating that MYB4 protein and mRNA are part of a negative autoregulatory loop. This feedback loop is altered in the sad2 mutant due to the absence of MYB4 protein in the nucleus, leading to the constitutive expression of MYB4 and C4H and resulting in accumulation of UV-absorbing pigments that shield the plant from UV-B radiation. © 2007 American Society of Plant Biologist.
- Kim, Y., Schumaker, K. S., & Zhu, J. (2006). EMS mutagenesis of Arabidopsis.. Methods in molecular biology (Clifton, N.J.), 323, 101-103.More infoPMID: 16739570;Abstract: A powerful approach for determining the biological functions of genes in an organism is to produce mutants with altered phenotypes and physiological responses. Various approaches for mutagenesis involving chemical, irradiation, and insertional methods have been developed; each has advantages and disadvantages for the study of gene function. In this post-genomic era, the use of reverse genetic approaches to understanding the role of genes in growth and development has become widespread. With development of new techniques such as targeting induced local lesions in genomes (TILLING), ethyl methanesulfonate (EMS) mutagenesis can be used for both forward and reverse genetic studies. Generation of diverse mutant alleles in the same gene provides critical tools to understand the role of these genes in the function of the organism. Here we describe the general method of EMS mutagenesis for the molecular genetic model plant Arabidopsis thaliana.
- Chinnusamy, V., Schumaker, K., & Zhu, J. (2004). Molecular genetic perspectives on cross-talk and specificity in abiotic stress signalling in plants. Journal of Experimental Botany, 55(395), 225-236.More infoPMID: 14673035;Abstract: The perception of abiotic stresses and signal transduction to switch on adaptive responses are critical steps in determining the survival and reproduction of plants exposed to adverse environments. Plants have stress-specific adaptive responses as well as responses which protect the plants from more than one environmental stress. There are multiple stress perception and signalling pathways, some of which are specific, but others may cross-talk at various steps. Recently, progress has been made in identifying components of signalling pathways involved in salt, drought and cold stresses. Genetic analysis has defined the Salt-Overly-Sensitive (SOS) pathway, in which a salt stress-induced calcium signal is probably sensed by the calcium-binding protein SOS3 which then activates the protein kinase SOS2. The SOS3-SOS2 kinase complex regulates the expression and activity of ion transporters such as SOS1 to reestablish cellular ionic homeostasis under salinity. The ICE1 (Inducer of CBF Expression 1)-CBF (C-Repeat Binding Protein) pathway is critical for the regulation of the cold-responsive transcriptome and acquired freezing tolerance, although at present the signalling events that activate the ICE1 transcription factor during cold stress are not known. Both ABA-dependent and -independent signalling pathways appear to be involved in osmotic stress tolerance. Components of mitogen-activated protein kinase (MAPK) cascades may act as converging points of multiple abiotic as well as biotic stress signalling pathways. Forward and reverse genetic analysis in combination with expression profiling will continue to uncover many signalling components, and biochemical characterization of the signalling complexes will be required to determine specificity and cross-talk in abiotic stress signalling pathways.
- Gong, D., Guo, Y., Schumaker, K. S., & Zhu, J. (2004). The SOS3 family of calcium sensors and SOS2 family of protein kinases in arabidopsis. Plant Physiology, 134(3), 919-926.More infoPMID: 15020756;PMCID: PMC523892;
- Guo, Y., Qiu, Q., Quintero, F. J., Pardo, J. M., Ohta, M., Zhang, C., Schumaker, K. S., & Zhu, J. (2004). Transgenic Evaluation of Activated Mutant Alleles of SOS2 Reveals a Critical Requirement for Its Kinase Activity and C-Terminal Regulatory Domain for Salt Tolerance in Arabidopsis thaliana. Plant Cell, 16(2), 435-449.More infoPMID: 14742879;PMCID: PMC341915;Abstract: In Arabidopsis thaliana, the calcium binding protein Salt Overly Sensitives (SOS3) interacts with and activates the protein kinase SOS2, which in turn activates the plasma membrane Na+/H+ antiporter SOS1 to bring about sodium ion homeostasis and salt tolerance. Constitutively active alleles of SOS2 can be constructed in vitro by changing Thr 168 to Asp in the activation loop of the kinase catalytic domain and/or by removing the autoinhibitory FISL motif from the C-terminal regulatory domain. We expressed various activated forms of SOS2 in Saccharomyces cerevisiae (yeast) and in A. thaliana and evaluated the salt tolerance of the transgenic organisms. Experiments in which the activated SOS2 alleles were coexpressed with SOS2 in S. cerevis/ae showed that the kinase activity of SOS2 is partially sufficient for SOS1 activation in vivo, and higher kinase activity leads to greater SOS1 activation. Coexpression of SOS3 with SOS2 forms that retained the FISL motif resulted in more dramatic increases in salt tolerance. In planta assays showed that the Thr168-to-Asp-activated mutant SOS2 partially rescued the salt hypersensitivity in sos2 and sos3 mutant plants. By contrast, SOS2 lacking only the FISL domain suppressed the sos2 but not the sos3 mutation, whereas truncated forms in which the C terminus had been removed could not restore the growth of either sos2 or sos3 plants. Expression of some of the activated SOS2 proteins in wild-type A. thaliana conferred increased satt tolerance. These studies demonstrate that the protein kinase activity of SOS2 is partially sufficient for activation of SOS1 and for salt tolerance in vivo and in planta and that the kinase activity of SOS2 is limiting for plant salt tolerance. The results also reveal an essential in planta role for the SOS2 C-terminal regulatory domain in salt tolerance.
- Qiu, Q., Guo, Y., Quintero, F. J., Pardo, J. M., Schumaker, K. S., & Zhu, J. (2004). Regulation of Vacuolar Na+/H+ Exchange in Arabidopsis thaliana by the Salt-Overly-Sensitive (SOS) Pathway. Journal of Biological Chemistry, 279(1), 207-215.More infoPMID: 14570921;Abstract: For plants growing in highly saline environments, accumulation of sodium in the cell cytoplasm leads to disruption of metabolic processes and reduced growth. Maintaining low levels of cytoplasmic sodium requires the coordinate regulation of transport proteins on numerous cellular membranes. Our previous studies have linked components of the Salt-Overly-Sensitive pathway (SOS1-3) to salt tolerance in Arabidopsis thaliana and demonstrated that the activity of the plasma membrane Na+/H+ exchanger (SOS1) is regulated by SOS2 (a protein kinase) and SOS3 (a calcium-binding protein). Current studies were undertaken to determine if the Na+/H+ exchanger in the vacuolar membrane (tonoplast) of Arabidopsis is also a target for the SOS regulatory pathway. Characterization of tonoplast Na +/H+ exchange demonstrated that it represents activity originating from the AtNHX proteins since it could be inhibited by 5-(N-methyl-N-isobutyl)amiloride and by anti-NHX1 antibodies. Transport activity was selective for sodium (apparent Km = 31 mM) and electroneutral (one sodium ion for each proton). When compared with tonoplast Na+/H+ activity in wild type, activity was significantly higher, greatly reduced, and unchanged in sos1, sos2, and sos3, respectively. Activated SOS2 protein added in vitro increased tonoplast Na+/H +-exchange activity in vesicles isolated from sos2 but did not have any effect on activity in vesicles isolated from wild type, sos1, or sos3. These results demonstrate that (i) the tonoplast Na+/H+ exchanger in Arabidopsis is a target of the SOS regulatory pathway, (ii) there are branches to the SOS pathway, and (iii) there may be coordinate regulation of the exchangers in the tonoplast and plasma membrane.
- Schumaker, K., Qiu, Q., Barkla, B. J., Vera-Estrella, R., Zhu, J., & Schumaker, K. S. (2003). Na+/H+ exchange activity in the plasma membrane of Arabidopsis. Plant physiology, 132(2).More infoIn plants, Na+/H+ exchangers in the plasma membrane are critical for growth in high levels of salt, removing toxic Na+ from the cytoplasm by transport out of the cell. The molecular identity of a plasma membrane Na+/H+ exchanger in Arabidopsis (SOS1) has recently been determined. In this study, immunological analysis provided evidence that SOS1 localizes to the plasma membrane of leaves and roots. To characterize the transport activity of this protein, purified plasma membrane vesicles were isolated from leaves of Arabidopsis. Na+/H+ exchange activity, monitored as the ability of Na to dissipate an established pH gradient, was absent in plants grown without salt. However, exchange activity was induced when plants were grown in 250 mm NaCl and increased with prolonged salt exposure up to 8 d. H+-coupled exchange was specific for Na, because chloride salts of other monovalent cations did not dissipate the pH gradient. Na+/H+ exchange activity was dependent on Na (substrate) concentration, and kinetic analysis indicated that the affinity (apparent Km) of the transporter for Na+ is 22.8 mm. Data from two experimental approaches supports electroneutral exchange (one Na+ exchanged for one proton): (a) no change in membrane potential was measured during the exchange reaction, and (b) Na+/H+ exchange was unaffected by the presence or absence of a membrane potential. Results from this research provide a framework for future studies into the regulation of the plant plasma membrane Na+/H+ exchanger and its relative contribution to the maintenance of cellular Na+ homeostasis during plant growth in salt.
- Parks, G. E., Dietrich, M. A., & Schumaker, K. S. (2002). Increased vacuolar Na+/H+ exchange activity in Salicornia bigelovii Torr. in response to NaCl. Journal of Experimental Botany, 53(371), 1055-1065.More infoPMID: 11971917;Abstract: Shoots of the halophyte Salicornia bigelovii are larger and more succulent when grown in highly saline environments. This increased growth and water uptake has been correlated with a large and specific cellular accumulation of sodium. In glycophytes, sensitivity to salt has been associated with an inability to remove sodium ions effectively from the cytoplasm in order to protect salt-sensitive metabolic processes. Therefore, in Salicornia bigelovii efficient vacuolar sequestration of sodium may be part of the mechanism underlying salt tolerance. The ability to compartmentalize sodium may result from a stimulation of the proton pumps that provide the driving force for increased sodium transport into the vacuole via a Na+/H+ exchanger. In current studies, increased vacuolar pyrophosphatase activity (hydrolysis of inorganic pyrophosphate and proton translocation) and protein accumulation were observed in Salicornia bigelovii grown in high concentrations of NaCl. Based on sodium-induced dissipation of a pyrophosphate-dependent pH gradient in vacuolar membrane vesicles, a Na+/H+ exchange activity was identified and characterized. This activity is sodium concentration-dependent, specific for sodium and lithium, sensitive to methyl-isobutyl amiloride, and independent of an electrical potential. Vacuolar Na+/H+ exchange activity varied as a function of plant growth in salt. The affinity of the transporter for Na+ is almost three times higher in plants grown in high levels of salt (Km=3.8 and 11.5 mM for plants grown in high and low salt, respectively) suggesting a role for exchange activity in the salt adaptation of Salicornia bigelovii.
- Qiu, Q., Guo, Y., Dietrich, M. A., Schumaker, K. S., & Zhu, J. (2002). Regulation of SOS1, a plasma membrane Na+/H+ exchanger in Arabidopsis thaliana, by SOS2 and SOS3. Proceedings of the National Academy of Sciences of the United States of America, 99(12), 8436-8441.More infoPMID: 12034882;PMCID: PMC123085;Abstract: Maintaining low levels of sodium ions in the cell cytosol is critical for plant growth and development. Biochemical studies suggest that Na+/H+ exchangers in the plasma membrane of plant cells contribute to cellular sodium homeostasis by transporting sodium ions out of the cell; however, these exchangers have not been identified at the molecular level. Genetic analysis has linked components of the salt overly sensitive pathway (SOS1-3) to salt tolerance in Arabidopsis thaliana. The predicted SOS1 protein sequence and comparisons of sodium ion accumulation in wild-type and sos1 plants suggest that SOS1 is involved directly in the transport of sodium ions across the plasma membrane. To demonstrate the transport capability of SOS1, we studied Na+/H+-exchange activity in wild-type and sos plants using highly purified plasma membrane vesicles. The results showed that plasma membrane Na+/H+-exchange activity was present in wild-type plants treated with 250 mM NaCl, but this transport activity was reduced by 80% in similarly treated sos1 plants. In vitro addition of activated SOS2 protein (a protein kinase) increased Na+/H+-exchange activity in salt-treated wild-type plants 2-fold relative to transport without added protein. However, the addition of activated SOS2 did not have any stimulatory effect on the exchange activity in sosl plants. Although vesicles of sos2 and sos3 plants had reduced plasma membrane Na+/H+-exchange activity, transport activity in both increased with the addition of activated SOS2 protein. These results demonstrate that SOS1 contributes to plasma membrane Na+/H+ exchange and that SOS2 and SOS3 regulate SOS1 transport activity.
- Xiong, L., Schumaker, K. S., & Zhu, J. (2002). Cell signaling during cold, drought, and salt stress. Plant Cell, 14(SUPPL.), S165-S183.More infoPMID: 12045276;PMCID: PMC151254;
- Hable, W. E., Oishi, K. K., & Schumaker, K. S. (1998). Viviparous-5 encodes phytoene desaturase, an enzyme essential for abscisic acid (ABA) accumulation and seed development in maize. Molecular and General Genetics, 257(2), 167-176.More infoPMID: 9491075;Abstract: The role of synthesis in the regulation of abscisic acid accumulation was investigated in the developing maize seed. To do this, expression and regulation of the abscisic acid biosynthetic enzyme phytoene desaturase were examined. Comparison of the gene sequence encoding phytoene desaturase and its transcript in the wild-type and viviparous-5 mutant showed that the mutant gene contains multiple insertions and deletions, resulting in the synthesis of a larger transcript. In addition, the 55-kDa phytoene desaturase protein was not detectable in the viviparous-5 mutant, indicating that this phenotype results from a mutation at the phytoene desaturase locus. Levels of phytoene desaturase transcript and protein were compared to abscisic acid levels during development to determine whether phytoene desaturase might regulate abscisic acid accumulation. In the endosperm, transcript levels were initially high and declined during late maturation and dormancy, while protein levels remained high throughout development. In the embryo, transcript levels were low and constant, while protein levels declined. Both temporal and tissue-specific expression of phytoene desaturase were unrelated to abscisic acid levels. An abscisic acid mutant (viviparous-2) deficient in phytoene desaturation was used to determine whether the wild-type protein encoded by Viviparous-2 regulates phytoene desaturase. Phytoene desaturase transcript and protein levels were compared in wild-type and viviparous-2 mutant embryos and endosperm. Normalized levels of phytoene desaturase were similar in wild-type and mutant tissues, suggesting that the wild-type Viviparous-2 protein does not regulate phytoene desaturase transcript or protein levels.
- Schumaker, K. S., & Dietrich, M. A. (1998). Hormone-induced signaling during moss development. Annual Review of Plant Physiology and Plant Molecular Biology, 49, 501-523.More infoAbstract: Understanding how a cell responds to hormonal signals with a new program of cellular differentiation and organization is an important focus of research in developmental biology. In Funaria hygrometrica and Physcomitrella patens, tho related species of moss, cytokinin induces the development of a bud during the transition from filamentous to meristematic growth. Within hours of cytokinin perception, a single-celled initial responds with changes in patterns of cell expansion, elongation, and division to begin the process of bud assembly. Bud assembly in moss provides an excellent model for the study of hormone-induced organogenesis because it is a relatively simple, well-defined process. Since buds form in a nonrandom pattern on cells that are not embedded in other tissues, it is possible to predict which cells will respond and where the ensuring changes will take place. In addition, bud assembly is amenable to biochemical, cellular, and molecular biological analyses. This review examines our current understanding of cytokinin-induced bud assembly and the potential underlying mechanisms, reviews the state of genetic analyses in moss, and sets goals for future research with this organism.
- Lin, H., Salus, S. S., & Schumaker, K. S. (1997). Salt sensitivity and the activities of the H+-ATPases in cotton seedlings. Crop Science, 37(1), 190-197.More infoAbstract: Salinity is a major problem confronting agriculture in arid environments. Sensitivity to high levels of salt in plants is associated with an inability to effectively remove Na+ ions from the cell cytoplasm. The ability to compartmentalize Na+ may result, in part, from stimulation of the H+-ATPases on the plasma membrane (PM-ATPase) and vacuolar membrane (V- ATPase). These H+-pumping ATPases may provide the driving force for Na+ transport via Na+-H+ exchangers. In a salt-sensitive line of cotton (Gossypium hirsutum L.), greater relative reductions in root length and root fresh weight than in hypocotyl length of seedlings grown in 75 mM NaCl indicated that the root was most affected by salt stress. To determine if the H+-ATPases are involved in the response to salt, we compared activities of the PM- and V-ATPases from roots in salt-sensitive cotton seedlings grown with or without 75 mM NaCl. Higher PM-ATPase activity (42%) was observed in seedlings grown in 75 mM NaCl. This stimulation was specific for Na+, was not observed when Na+ was added to membrane fractions, and was not due to an increase in PM-ATPase protein levels. V-ATPase protein accumulation was unaffected by growth in the presence of Na+, and activity was unaffected by Na+ in the growth medium or by Na+ added to membrane fractions. These studies suggest that although the PM-ATPase responds to increased Na+, activity of the transport proteins on the plasma membrane alone may be insufficient to regulate intracellular Na+ levels. In addition, the inability of the V-ATPase to respond to increased levels of Na+ indicates that salt sensitivity in cotton seedlings may result, in port, from a lack of effective driving force for compartmentalization of Na+.
- Schumaker, K. S., & Dietrich, M. A. (1997). Programmed changes in form during moss development. Plant Cell, 9(7), 1099-1107.
- Schumaker, K. S., & Gizinski, M. J. (1996). G proteins regulate dihydropyridine binding to moss plasma membranes. Journal of Biological Chemistry, 271(35), 21292-21296.More infoPMID: 8702906;Abstract: The role of calcium as an activator and regulator of many biological processes is linked to the ability of the cell to rapidly change its cytoplasmic calcium levels. Calcium acts as an intracellular messenger in hormone-induced bud formation during the development of the moss Physcomitrella patens. Calcium transport and ligand binding studies have implicated plasma membrane-localized 1,4-dihydropyridine (DHP)-sensitive calcium channels in this increase in cellular calcium. To understand the regulation of the moss calcium channel, we investigated the involvement of GTP binding regulatory proteins (G proteins). Guanosine 5'-(γ- thio)triphosphate (GTPγS), a nonhydrolyzable GTP analog that locks G proteins into their active state, stimulated DHP binding to high affinity receptors in the moss plasma membrane. DHP binding was measured as the ability of the DHP agonist Bay K8644 or the DHP antagonist nifedipine to compete with the DHP arylazide [3H]azidopine for binding to moss plasma membranes. G protein stimulation of binding was seen when competition was carried out with either nifedipine or Bay K8644. G proteins regulated the rates of association and dissociation of bound [3H]azidopine, and stimulation was dependent on GTPγS concentration. Guanosine 5'-(β- thio)diphosphate, a GDP analog that locks G proteins into their inactivated state, did not affect the dose dependence of either the agonist or the antagonist. These results suggest that G proteins may act via a membrane- delimited pathway to regulate calcium channels in the moss plasma membrane.
- Schumaker, K. S., & Gizinski, M. J. (1995). 1,4-Dihydropyridine binding sites in moss plasma membranes: Properties of receptors for a calcium channel antagonist. Journal of Biological Chemistry, 270(40), 23461-23467.More infoPMID: 7559508;Abstract: University of Arizona,. An increase in cytoplasmic calcium is an early event in hormone (cytokinin)-induced vegetative bud formation in the moss Physcomitrella patens. Whole cell and calcium transport studies have implicated 1,4-dihydropyridine-sensitive calcium channels in this increase in cellular calcium. To understand the molecular nature of the dihydropyridine-sensitive calcium channel, we have established conditions for the binding of the arylazide 1,4-dihydropyridine, [3H]azidopine, to its receptor in moss plasma membranes. [3H]Azidopine bound specifically in a saturable and reversible manner. The KD for [3H]azidopine binding was 5.2 nM and the Bmax was 35.6 pmol/mg of protein. Association and dissociation of the receptor and [3H]azidopine were temperature-dependent, and association varied as a function of pH. Binding was inhibited by dihydropyridine, phenylalkylamine, and benzothiazepine calcium channel blockers, bepridil, lanthanum, and N-ethylmaleimide. [3H]Azidopine binding was stimulated by cations including calcium, strontium, manganese, and barium. [3H]Azidopine binding was also stimulated by cytokinin with a Km value for kinetin of 0.13 nM. These studies utilize a simple plant system to provide a biochemical framework for understanding calcium regulation during development and have implications for understanding mechanisms of signal transduction in plants.
- Schumaker, K. S., & Gizinski, M. J. (1993). Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts. Proceedings of the National Academy of Sciences of the United States of America, 90(23), 10937-10941.More infoPMID: 7504288;PMCID: PMC47896;Abstract: Ca2+ influx through dihydropyridine (DHP)-sensitive Ca2+ channels is thought to be an early event in cytokinin-induced bud formation in moss protonema because DHP antagonists inhibit bud formation in the presence of cytokinin and DHP agonists stimulate bud formation in the absence of cytokinin [Conrad, P. A. & Hepler, P. K. (1988) Plant Physiol. 86, 684-687]. In the present study, we established the presence of a DHP-sensitive Ca2+ transport system by measuring 45Ca2+ influx into moss protoplasts. Ca2+ influx was stimulated by external KCI (up to 5 mM), indicating that transport is voltage-dependent. K+-induced Ca2+ influx was DHP-sensitive with >50% inhibition at 500 nM nifedipine. Ca2+ influx was stimulated by increasing concentrations of the DHP Ca2+ channel agonist Bay K8644 with half-maximal effects at 25 nM; this stimulation was seen only in the absence of K+, suggesting that the agonist works preferentially on polarized membranes. Ca2+ influx was also inhibited by phenylalkylamines (verapamil) and benzothiazepines (diltiazem). The phytohormone 6-benzylaminopurine consistently stimulated Ca2+ influx with a Km value of 1 nM, whereas adenine, indoleacetic acid, and gibberellic acid had no effect on Ca2+ transport. The cytokinins kinetin and trans-zeatin caused a greater stimulation of Ca2+ influx and induced more bud formation than did 6-benzylaminopurine. These results indicate that Ca2+ is taken up into moss protoplasts through voltage-dependent DHP-sensitive Ca2+ channels on the plasma membrane and that one of the cytokinin effects in the induction of bud formation is regulation of this plasma membrane Ca2+ channel.
- Schumaker, K. S., & Sze, H. (1990). Solubilization and reconstitution Of the oat root vacuolar H+/Ca2+ exchanger. Plant Physiology, 92(2), 340-345.More infoPMID: 16667279;PMCID: PMC1062295;Abstract: Calcium is sequestered into vacuoles of oat (Avena sativa L.) root cells via a H+/Ca2+ antiporter, and vesicles derived from the vacuolar membrane (tonoplast) catalyze an uptake of calcium which is dependent on protons (pH gradient [ApH] dependent). The first step toward purification and identification of the H+/Ca2+ antiporter is to solubilize and reconstitute the transport activity in liposomes. The vacuolar H+/Ca2+ antiporter was solubilized with octylglucoside in the presence of soybean phospholipids and glycerol. After centrifugation, the soluble proteins were reconstituted into liposomes by detergent dilution. A ΔpH (acid inside) was generated in the proteoliposomes with an NH4Cl gradient (NH4+in ≫ NH4+out) as determined by methylamine uptake. Fundamental properties of ΔpH dependent calcium uptake such as the Km, for calcium (∼15 micromolar) and the sensitivity to inhibitors such as N,N′-dicyclohexylcarbodiimide, ruthenium red, and lanthanum, were similar to those found in membrane vesicles, indicating that the H+/Ca2+ antiporter has been reconstituted in active form.
- Schumaker, K. S., & Sze, H. (1987). Inositol 1,4,5-trisphosphate releases Ca2+ from vacuolar membrane vesicles of oat roots.. Journal of Biological Chemistry, 262(9), 3944-3946.More infoPMID: 2881929;Abstract: In plant cells, transient changes in cytoplasmic Ca2+ levels can modulate numerous developmental processes. Ca2+ is accumulated in the vacuole via a H+/Ca2+ antiport system that is energized by the tonoplast H+-pumping ATPase. Inositol 1,4,5-triphosphate (InsP3), but not inositol 1,4-bisphosphate, myo-inositol 1-phosphate, or fructose 2,6-bisphosphate, caused a transient reduction of Ca2+ levels in tonoplast vesicles. The decrease was dependent on InsP3 concentration (Km apparent = 0.6 microM). The InsP3-induced Ca2+ release was blocked by the Ca2+ antagonist, 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate-HCl. These results suggest that the vacuolar membrane is one target site for InsP3 action and that InsP3 may operate as a second messenger in the mobilization of intracellular Ca2+ in plant cells.
- Schumaker, K. S., & Sze, H. (1986). Calcium transport into the vacuole of oat roots. Characterization of H+/Ca2+ exchange activity.. The Journal of biological chemistry, 261(26), 12172-12178.More infoPMID: 2427517;Abstract: Calcium (Ca2+) is sequestered into vacuoles of oat root cells through a H+/Ca2+ antiport system that is driven by the proton-motive force of the tonoplast H+-translocating ATPase. The antiport has been characterized directly by imposing a pH gradient in tonoplast-enriched vesicles. The pH gradient was imposed by diluting K+-loaded vesicles into a K+-free medium. Nigericin induced a K+/H+ exchange resulting in a pH gradient of 2 (acid inside). The pH gradient was capable of driving 45Ca2+ accumulation. Ca2+ uptake was tightly coupled to H+ loss as increasing Ca2+ levels progressively dissipated the steady state pH gradient. Ca2+ uptake displayed saturation kinetics with a Km(app) for Ca2+ of 10 microM. The relative affinity of the antiporter for transport of divalent cations was Ca2+ greater than Sr2+ greater than Ba2+ greater than Mg2+. La3+ or Mn2+ blocked Ca2+ uptake possibly by occupying the Ca2+-binding site. Ruthenium red (I50 = 40 microM) and N,N'-dicyclohexylcarbodiimide (I50 = 3 microM) specifically inhibited the H+/Ca2+ antiporter. When driven by pH jumps, the H+/Ca2+ exchange generated a membrane potential, interior positive, as shown by [14C]SCN accumulation. Furthermore, Ca2+ uptake was stimulated by an imposed negative membrane potential. The results support a simple model of one Ca2+ taken up per H+ lost. The exchange transport can be reversed, as a Ca2+ gradient (Ca2+in greater than Ca2+out) was effective in forming a pH gradient (acid inside). We suggest that the H+/Ca2+ exchange normally transports Ca2+ into the vacuole; however, under certain conditions, Ca2+ may be released into the cytoplasm via this antiporter.
- Schumaker, K. S. (2014, May). Linking calcium sensor gene duplication and functional divergence to plant adaptation to salinity. Washington Area Society of Plant Biologists Symposium. College Park Maryland: Washington Area Society of Plant Biologists.
- Zhang, S., Wang, D., Zhang, H., Lloyd, A., Skaggs, M. I., An, L., Drews, G. N., Schumaker, K. S., & Yadegari, R. (2012, July). Polycomb repressive complex 2 regulates type I MADS-box gene expression during endosperm development in Arabidopsis. Plant Biology 2012. Austin, TX.More infoAlso an oral presentation by Shanshan Zhang in a minisymposium.