M.S., Biochemistry, Swiss Federal Institute of Technology, Switzerland
Ph.D., Biology, University of California, San Diego
Plants are continuously exposed to potential pathogens, yet most plants are resistant to most pathogens. Plants have evolved a surveillance system with similarities to the innate immune system of animals that detects invading pathogens.
Specifically, plants express a large number of resistance genes that, directly or indirectly, interact with effector proteins of pathogens and trigger a plant disease resistance response. Pathogens in turn evolve to overcome this resistance, either by deleting or altering the detected effector proteins or directly counteracting the plant response.
The co-evolution of host and pathogen is evident in the large number of pathogen strains within a given species expressing specific effector proteins, and in the large number of plant disease resistance genes. It is estimated that Arabidopsis has devoted more than one percent of its genome just to resistance genes.
Walter Gassman’s research is aimed at understanding the function of this important class of plant genes. He and his colleagues are focusing on the Arabidopsis RPS4 gene specifying resistance to Pseudomonas syringae expressing the cognate avirulence gene avrRps4.
RPS4 was isolated by map-based cloning and belongs to the TIR-NBS-LRR class of plant disease resistance genes. This class shows homology at the N-terminus of the predicted protein to known proteins involved in the animal innate immune response.
For a detailed analysis of the TIR-NBS-LRR gene-dependent disease resistance signaling pathway. Walter Gassmann’s lab studies alternative splicing and the structure/function relationship of the RPS4 gene products. In addition, genetic screens of randomly mutagenized Arabidopsis plants for mutants in the RPS4 signaling pathway are being performed.
For example, the lab has isolated mutants in the naturally avrRps4-susceptible Arabidopsis accession RLD that are now specifically resistant to bacteria expressing avrRps4, but do not show general enhanced resistance.
One of these suppressor genes, SRFR1, was recently cloned and encodes a highly conserved protein of unknown function with partial similarity to transcriptional repressors in other organisms. The function of the SRFR1 protein and how it fits into the plant innate immune response pathway is a current focus of the Gassmann lab.
Durbak AR, Phillips KA, Pike S, O’Neill MA, Mares J, Gallavotti A, Malcomber ST, Gassmann W, and McSteen P. Transport of boron by the tassel-less1 aquaporin is critical for vegetative and reproductive development in maize. Plant Cell 2014; doi: 10.1105/tpc.114.125898.
Kim SH, Son GH, Bhattacharjee S, Kim HJ, Nam JC, Nguyen PDT, Hong JC, and Gassmann W. The Arabidopsis immune adaptor SRFR1 interacts with TCP transcription factors that redundantly contribute to effector-triggered immunity. Plant J. 2014;78: 978-989.
Pike S, Gao F, Kim MJ, Kim SH, Schachtman D, and Gassmann W. Members of the NPF3 transporter family encode pathogen-inducible nitrate/nitrite transporters in grapevine and Arabidopsis. Plant Cell Physiol. 2014;55: 162-170.
Léran S, Varala K, Boyer JC, Chiurazzi M, Crawford N, Daniel-Vedele F, David L, Dickstein R. Fernandez E, Forde B, Gassmann W, Geiger D, Gojon A, Gong JM, Halkier BA, Harris JM, Hedrich R, Limami AM, Rentsch D, Seo M, Tsay YF, Zhang M, Coruzzi G, and Lacombe B. A unified nomenclature of NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family members in plants. Trends Plant Sci. 2014;19: 5-9.
Howard BE, Hu Q, Babaoglu AC, Chandra M, Borghi M, Tan X, He L, Winter-Sederoff H, Gassmann W, Veronese P and Heber S. High-throughput RNA sequencing of Pseudomonas-infected Arabidopsis reveals hidden transcriptome complexity and novel splice variants. PLoS ONE 2013;8: e74183.
Bhattacharjee S, Garner CM, and Gassmann W. New clues in the nucleus: transcriptional reprogramming in effector-triggered immunity. Front. Plant Sci. 2013;4:364.
Kim T-H, Kunz H-H, Bhattacharjee S, Hauser F, Park JY, Engineer C, Liu A, Ha T, Parker JE, Gassmann W, and Schroeder J.I Natural variation in small molecule-induced TIR-NB-LRR signaling induces root growth arrest via EDS1- and PAD4-complexed R protein VICTR. Plant Cell 2012;24:5177-5192
Gassmann W, and Bhattacharjee S. (2012) Effector-triggered immunity signaling: from gene-for-gene pathways to protein-protein interaction networks. Mol. Plant-Microbe Interact. 2012;25: 862-868 (pdf).
Zhang XC and Gassmann W. Quantifying alternatively spliced mRNA via capillary electrophoresis. Methods in Molecular Biology 2011(Clifton, N.J.);712:69-77.
Li JY, Fu YL, Pike SM, Bao J, Tian W, Zhang Y, Chen CZ, Li HM, Huang J, Li LG, Schroeder JI, Gassmann W and Gong JM. The Arabidopsis nitrate transporter NRT1.8 functions in nitrate removal from the xylem sap and mediates cadmium tolerance. Plant Cell 2010;22(5):1633-1646.
Gao F, Shu X, Ali MB, Howard S, Li N, Winterhagen P, Qiu W, Gassmann W. A functional EDS1 ortholog is differentially regulated in powdery mildew resistant and susceptible grapevines and complements an Arabidopsis eds1 mutant. Planta 2010;231(5): 1037-1047.
Kim SH, Gao F, Bhattacharjee S, Adiasor JA, Nam JC, and Gassmann W. The Arabidopsis resistance-like gene SNC1 is activated by mutations in SRFR1 and contributes to resistance to the bacterial effector AvrRps4. PLoS Pathogens 2010;6(11): e1001172. doi10.1371/journal.ppat.1001172
Pike S, Patel A, Stacey G, Gassmann W. Arabidopsis OPT6 is an oligopeptide transporter with exceptionally broad substrate specificity. Plant and Cell Physiology 2009;50(11):1923-1932.
Kim SH, Kwon SI, Saha D, Anyanwu NC, Gassman W. Resistance to the Pseudomonas syringae effector HopA1 is governed by TIR-NBS-LRR Protein rps6 and is enhanced by mutations in SRFR1. Plant Physiology 2009;150:1723-1732.
Gassmann W. Alternative splicing in plant defense. Current Topics in Microbiology and Immunology 2008;326:219-233.
Stacey MG, Patel A, McClain WE, Mathieu M, Remley M, Rogers EE, Gassmann W, Blevins DG, and Stacey G. The Arabidopsis AtOPT3 protein functions in metal homeostasis and movement of iron to developing seeds. Plant Physiology 2008;146:589-601.
Zhang XC, and Gassmann W. Alternative splicing and mRNA levels of the disease resistance gene RPS4 are induced during defense responses. Plant Physiology 2007;145: 1577-1587.
Durrett TP, Gassmann W, and Rogers EE. The FRD3-mediated efflux of citrate into the root vasculature is necessary for efficient iron translocation. Plant Physiol. 2007;144, 197-205.
Liu Y, Ren D, Pike S, Pallardy S, Gassmann W, and Zhang S. Chloroplast-generated reactive oxygen species are involved in hypersensitive response-like cell death mediated by a mitogen-activated protein kinase cascade. Plant J. 2007;51(6):941-954.