Poster: Plant Pathogen/Symbiont Interactions

Abs # 740: The type III avirulence gene is a major virulence determinant in bacterial blight of rice

Presenter:	Yang, Bing , byang@ksu.edu
Authors	Yang, Bing  (A)   Johnson, Lowell B. (A)   White, Frank F (A)
Affiliations:	(A): Department of Plant Pathology, Kansas State University

Avirulence gene products of phytopathogenic bacteria are secreted from the bacteria by a type III secretion pathway and elicit resistance in host plants that carry the corresponding gene for resistance (R-gene). Proteins from type III secretory mechanisms of animal pathogenic bacteria are known largely as effectors of virulence. In contrast, few avirulence proteins are known to have a determinant role in virulence for phytopathogens. We described four genes of the avrBs3/pthA gene family that have a dramatic effect on the virulence of the respective strain of X. oryzae pv. oryzae, the causal agent of bacterial blight of rice. Each gene has a distinct central repeat domain but fully complement each other for virulence. The avrXa7 gene is the only gene of this group known to have virulence and avirulence activity in rice. Mutation of the repeat region of avrXa7 by deleting and swapping the repeat units in vitro or in vivo resulted in the variation of avrXa7 specificity and genes with only virulence activity. We extrapolate the results to indicate that the bacterial blight complex of rice is highly dependent on the avrBs3/pthA type III effectors. The results also demonstrate the potential of the strains to maintain virulence upon deployment of the corresponding R-gene.