Characterization of Avirulence Genes from Pseudomonas syringae pv. tomato

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This laboratory has cloned and characterized several avirulence genes from bacterial pathogens in the Pseudomonas syringae group that are responsible for defensive surveillance by soybean plants. One of these genes, avrD from P. syringae pv. tomato, causes bacterial hosts to elaborate an extracellular elicitor compound. The isolated elicitor causes the hypersensitive response (HR) only on soybean cultivars containing thecomplementary disease resistance gene, Rpg4. AvrD also has several other interesting features such as its occurrence, along with four other linked genes, on an indigenous bacterial plasmid and its 100-fold induction when bacteria are grown in soybean leaves as compared to culture media. The interaction of bacteria carrying avrD with plant hosts therefore involves reciprocal signalling mechanisms that initiate precise developmentalprograms in both organisms. This proposal requests support to further study avrD and its role in initiating plant disease resistance by 1) characterizing the avrD elicitor; 2) elucidating the nature of plant induction of avrD; 3) studying the indigenous plasmid on which avrD occurs and 4) comparing avrD withhomologous genes that occur in other P. syringae pathovars. The proposed research should contribute significantly to our understanding of plant-microbe signalling mechanisms and disease resistance in plants.