Isolation and Characterization of Pseudomonas Type III Effectors That Suppress Programmed Cell Death in Eukaryotes

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Pseudomonas syringae is a pathogen whose interactions with plants can take two strikingly different courses. In virulent interactions with susceptible plants, bacteria cause disease, whereas in avirulent interactions with resistant plants, bacteria trigger a rapid, defense-associated programmed cell death (PCD) known as the hypersensitive response (HR). Both outcomes are controlled by bacterial proteins injected into plant cells by a protein delivery system called the type III secretion system (TTSS). Preliminary data on this project show that several bacterial proteins act as suppressors of the HR. Remarkably, these PCD suppressors also function to inhibit yeast apoptosis (a type of PCD found in animals) and inhibit the ability of the mouse pro-apoptotic protein, Bax, to induce apoptosis in plants and yeast. This indicates that these proteins function as anti-apoptotic factors in a trans-kingdom manner. This project will use screens in yeast and plant systems to isolate additional bacterial proteins that act as PCD suppressors. Moreover, the project will characterize each suppressor to determine their general effect on other hallmarks of plant defense. The experiments described in this project offer broad training for students. Besides current approaches in microbiology, plant biology, and functional genomics, the topics pursued have important ramifications for mammalian systems, greatly adding to the breadth of this research program. The researchers have participated with the establishment of the UNL Young Nebraska Scientist (YNS) program, designed to enhance the recruitment of minority high school students who have demonstrated interest in the life sciences. The program is unusual in that it provides mentorship to the student from high school through their undergraduate career. Also, the researchers have initiated collaboration with Nebraska Wesleyan University, an excellent liberal arts college. Thus, the research group will enhance its pool of undergraduates, many of which are from under-represented ethnic groups.