CAREER: The Role of the HrpR/S Proteins in the Regulation of Virulence in the Plant Pathogenic Bacterium Pseudomonas syringae.

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Intellectual Merit: Pseudomonas syringae is an economically significant bacterial pathogen of many crop plants. The disease is characterized by the appearance of necrotic lesions on the leaves and fruits of infected plants. P. syringae expresses virulence genes, including those encoding a multi-component Type III secretion system (T3SS) which is necessary to colonize the plant host. The T3SS delivers bacterial effector proteins directly into host cells. Effectors disrupt plant signaling pathways and undermine plant defense responses. Other P. syringae virulence genes are involved in the synthesis of phytotoxins, which are low molecular weight compounds that damage plant cells or influence disease development. In most bacteria, including P. syringae, virulence gene expression is tightly regulated in response to environmental signals that exist in the host. This project focuses on HrpR and HrpS, two regulators of P. syringae virulence gene expression that function in a complex regulatory circuit. In this circuit, HrpR and HrpS activate expression of the hrpL gene, which encodes a direct regulator of T3SS, effector, and phytotoxin biosynthesis genes. Several aspects of the HrpRS regulatory cascade are not well characterized. In particular, this project will address the Hrp regulatory expression pattern in plants that are normally infected by P. syringae. The specific objectives of the research are to: (i) determine the DNA binding sites for HrpR and HrpS upstream of the hrpL gene, (ii) identify genes in P. syringae other than hrpL that are directly regulated by HrpR and HrpS, and (iii) examine the regulation of hrpRS by environmental signals. This objective will also include expression studies in and on the plant. Learning more about how HrpR and HrpS control virulence gene expression will contribute to a better understanding of how P. syringae initiates plant infection and manipulates plant physiology. Integrated Research/Teaching program: The project also includes efforts by the principal investigator to develop an integrated teaching/research/outreach program. A partnership will be developed with the Youth Exploring Science (YES) program, which educates disadvantaged high school students from underrepresented minorities. As part of this educational outreach program, a course will be developed at the University of Missouri-St. Louis in which undergraduates create interactive learning activities related to plant-microbe interactions. The university students will then facilitate these activities with the YES high school students in a seven part program at the St. Louis Science Center. The high school students also will be employed by the St. Louis Science Center during the summer to adapt some of the plant-microbe interactions activities for presentation to the general public.Broader impacts: HrpR and HrpS are appropriate targets for the development of new control measures, which may also be effective against other important plant pathogens. The project will support also the training of graduate and undergraduate students in plant pathology and molecular biology research. These students will gain expertise in a variety of molecular, genetic, biochemical, and bioinformatic techniques that will enhance their future career opportunities in the biological sciences.