This project seeks to identify critical plant processes affected during bacterial pathogenesis, opening the door to the discovery of alternative methods to control or eliminate plant disease. The investigators will use genetic, biochemical, and cell biological approaches to determine how pathogenic bacteria suppress plant defenses to promote colonization. The disease that will be studied is bacterial spot disease of tomato caused by Xanthomonas campestris pathovar vesicatoria (Xcv). Xcv has evolved a specialized secretion system (referred to as the type III secretion system (TTSS)) to transport 30-35 proteins into the plant cell during infection. The intellectual goal of this project is to determine the biochemical function of XopN, a unique Xcv protein that is highly conserved amongst different Xanthomonas species. The central hypothesis is that XopN interferes with protein-protein interactions in tomato to suppress defense activation. The specific aims are to: (1) characterize XopN protein domains required for Xcv pathogenesis in tomato; (2) characterize a tomato protein that XopN binds to at the plant plasma membrane; and (3) identify and characterize plant pathways specifically modulated by XopN during Xcv infection. Knowledge gain herein will contribute to the mechanistic understanding of microbial pathogenesis and the regulation of defense pathways in plants.
Broader Impacts: In the long-term, knowledge gained herein will be used by academia, industry, and the government to address agricultural production, disease prevention, and eradication. In the short-term, the investigators will work with K-12 teachers in Fremont CA and their students to introduce this plant topic. Currently, a plant biology curriculum is not being taught. Emphasis will be to train students and teachers about plant biology, disease, and agriculture - highlighting the importance of the plant sciences and its impact on society.
PROJECT GOALS: The goal of this project was to identify specific defense pathways in plants that are affected during bacterial pathogensis. Insight to the mechanisms by which pathogens suppress plant immunity will provide fundamental knowledge that can be used to comprehensively understand how the plant defense network operates and to engineer novel methods to control and/or elimiante plant disease. This infomration will also be relevant for the study of human and animal diseases considering that hte mechanisms by which pathogens alter plant and animal physiology are remarkably similar, even though the cellular components are not always conserved. Ultimately, industry and government will use this information to develop and implement economically sustainable agricultural practicies that consider human health and world growth. INTELLECTUAL MERIT – Summary of new knowledge gained from grant: We studied the early interactions that occur between the bacterial pathogen Xanthomonas euvesicatoria and its host plant tomato. Xanthomonas euvesicatoria is the causal agent of bacterial spot, one of the most important diseases of tomato worldwide, causing significant losses in tropical and subtropical zones. In this project, we: (1) developed tools and assays to study the early defense responses trigged in tomato leaves in response to Xanthomonas infection; (2) discovered two proteins required for early anti-Xanthomonas tomato defense responses; and (3) provide evidence that a pathogen virulence factor targets these defense proteins to suppress immunity in tomato. Collectively, these research activities provide novel insight to the defense machinery required to combat Xanthomonas infection and identify potential mechanism by which Xanthomonas suppresses these defenses to promote disease in an important crop plant. BROADER IMPACTS – Training: This grant provided close, hands-on research training at Stanford University for 1 graduate student, 2 post-doctoral scholars, 6 undergraduates, 1 lab assistant, 2 community college students, 10 high school (H.S.) students, 3 H.S. teachers, 2 international scholars (India and China), and 1 international graduate student (France). This included 17 men, 11 women, 4 URMs, and 2 first-generation. High School Outreach: Prior to 2007, no plant biology was being taught at some local high schools. Via the IISME (Industry Initiatives for Science and Math Education)/Stanford Summer Program, H.S. teachers were hosted to provide state-of-the-art training to develop new curricula and labs focused on plant biology. H.S. students were hosted via the Stanford RISE (raising interest in science and engineering) summer internship program and IISME activities during academic year. Resources for research & education: Project provided instrumentation, reagents, consultation, and lectures to support: (1) training of H.S. teachers and students; (2) development of H.S. labs and annual science fair projects; (3) two international scholars working directly with farmers and emerging pathogens in the field; (4) one international student pursuing Xanthomonas pathology. Community building: The Principal Investigator was a co-organizer of a BARD workshop on "Microbial Virulence Determinants and Plant Innate Immunity" in Israel to disseminate research findings, debate the direction of current and future research, and establish new collaborations to advance research in this field. The workshop was designed to engage young and under-represented scientists, and enhance communication and infrastructure between plant biologists in the United States and Israel.
