Functional Genomics Approach to Identify Signaling Components Involved in Defense Responses Induced by the Ethylene Inducing Xyalanase Elicitor

Plant-microbe interactions involve a large number of global regulatory systems, which are essential for plants to protect themselves against pathogen attack. An ethylene-inducing xylanase (EIX) of Trichoderma viride is a potent elicitor of plant defense responses, like hypersensitive response (HR), in specific cultivars of tobacco (Nicotiana tabacum) and tomato (Lycopersicon esculentum). The central goal of this proposal was to investigate the molecular mechanisms that allow plants to specifically activate defense responses after EIX treatment. We proposed to identify cellular signaling components involved in the induction of HR by the EIX elicitor. The molecular genetic analysis of the signal transduction pathway that modulates hypersensitive responses is an important step in understanding the induction of plant defense responses. The genes that mediate LeEIX2-EIX dependent activation of resistance mechanisms remain to be identified. We used two approaches to identify the cellular signaling components that induce HR mediated by the EIX elicitor. In the first approach, we performed a yeast two-hybrid screening using LeEix2 as bait to identify plant proteins that interact with it. In the second approach, we used virus-induced gene silencing (VIGS) for a high-throughput screen to identify genes that are required for the induction of LeEIX2-EIX mediated HR. VIGS will also be used for functional characterization of genes that will be identified during the yeast two-hybrid screen. This investigation will shed light on cellular processes and signaling components involved in induction of general plant defense against pathogens and will provide the basis for future biotechnological approaches to improve plant resistance to pathogens. Several genes were indentified by the two approaches. We used the VIGS and yeast two hybrid approaches to confirm that activity of the genes initially identified by different procedure. Two genes inhibit the induction of HR by the fungal elicitor in the different systems; Tobacco-Harpin binding protein 1 and cyclopropyl isomerase.