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Multiple Adhesin-Like Functions of Xanthomonas oryzae pv. oryzae Are Involved in Promoting Leaf Attachment, Entry, and Virulence on Rice

Xanthomonas oryzae pv. oryzae is the causal agent of bacterial blight of rice. We have used enhanced green fluorescent protein-tagged X. oryzae pv. oryzae cells in conjunction with confocal microscopy to monitor the role of several adhesin-like functions in bacterial adhesion to leaf surface and early stages of leaf entry. Mutations in genes encoding either the Xanthomonas adhesin-like protein A (XadA) or its paralog, Xanthomonas adhesin-like protein B (XadB), as well as the X. oryzae pv. oryzae homolog of Yersinia autotransporter-like protein H (YapH), exhibit deficiencies in leaf attachment or entry. A mutation in the X. oryzae pv. oryzae pilQ gene, which is predicted to encode the type IV pilus secretin, appears to have no effect on leaf attachment or entry. The xadA^-- mutant is deficient in the ability to cause disease following surface inoculation while the XadB, YapH, and PilQ functions are less important than XadA for this process. The xadA^-- and xadB^-- mutants have no effect on virulence following wound inoculation whereas the yapH^-- and pilQ^-- mutants are always virulence deficient following wound inoculation. Overall, these results indicate that multiple adhesin-like functions are involved in promoting virulence of X. oryzae pv. oryzae, with preferential involvement of individual functions at different stages of the disease process.