Regulation of Arabidopsis immune function through RIN4 sub-cellular localization and exocyst interaction

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Plants employ a branched immune system that prevents disease in the vast majority of plant-microbe interactions. One branch recognizes pathogen associated molecular patterns (PAMPs) that are contained within conserved microbial molecules. A second branch recognizes effector proteins, which are pathogen-encoded virulence factors. These two branches utilize common signaling pathways and induce common outputs, yet little is known about the mechanistic basis of intersections within the network they comprise. The RIN4 protein of the model plant Arabidopsis thaliana is a hub protein with key roles in regulating both branches, thus a detailed understanding of RIN4 will provide fundamental insight into the function of the plant immune system. The work will address three aspects of RIN4 function. Changes in the sub-cellular localization of RIN4, which are induced by bacterial effector proteins, have distinct effects on the activity of the two branches of the plant immune system. The proposed work will determine how sub-cellular localization of RIN4 affects its defense regulatory function. Preliminary data also indicate that RIN4 interacts with components of the plant exocyst, which is a multi-protein complex that regulates vesicle trafficking and membrane fusion events that play important roles in the function of the plant immune system. The proposed work will determine how interaction of the exocyst with RIN4 contributes to plant immune function. Finally, RIN4 functions in guard cells to regulate stomatal aperture in response to bacterial infection. The ability of plants to prevent invasion by epiphytically growing bacterial pathogens depends on their ability to close and keep closed their stomata. Control of guard cell function by RIN4 and bacterial effector proteins that target RIN4 will be investigated. The research aims will be addressed using plant pathology, molecular, biochemical, and cell biological methods.Broader Impacts: The trend to use agriculture to fuel as well as feed the world places great demand on optimizing crop productivity. To most effectively breed and/or engineer disease resistance in food and biofuel crops while minimizing deleterious side effects, such as reduced yield, requires fundamental knowledge about connections within the network comprising the plant immune system. Though the work will be done in the Arabidopsis thaliana model system, the findings will be applicable to agriculturally important plants, as RIN4 homologs have been identified in all land plants examined and demonstrated to play important roles in immune function of several crop plants. Findings will be presented at meetings and published in peer-reviewed journals. The PI has a proven record of working with underserved groups at the undergraduate, graduate, and post-doctoral levels, including the recent graduation of an Hispanic Ph.D. student. Funds from the project will also support participation of students from small liberal arts colleges in the Summer Undergraduate Research Experience program at The Ohio State University. Finally, the PI will participate in the organization and instruction of a module focusing on the plant immune system during the 2012 Summer Practical Workshop in Functional Genomics at Ohio State.