(The) type III effector XopN of Xanthomonas oryzae pv. oryzae Targets OsVOZ2 and a putative thiamine synthase in rice

Abstract

Bacterial leaf blight on rice, one of the most serious rice diseases, is caused by Xanthomonas oryzae pv. oryzae (Xoo). To determine roles of Xanthomonas outer proteins (Xop) in Xoo, I identified seven Xop homologs from the genome information of Xoo KXO85. The xopQKXO85, xopXKXO85, xopP2KXO85, xopP1KXO85, and xopNKXO85 were generated by EZ-Tn5 mutagenesis. Among the individual mutants, the xopP2KXO85, xopP1KXO85 and xopNKXO85 mutants exhibited significantly reduced virulence compared to the wild-type in the flag leaves of Dongjin. Interestingly, I did not see reduced virulence when the xopP2KXO85, xopP1KXO85 and xopNKXO85 mutants were inoculated into young leaves of the Dongjin. This indicated that Xop-mediated virulence is dependent on leaf stages in rice. To identify target proteins of XopNKXO85 in rice, I performed yeast two-hybrid screening. Two rice proteins, OsVOZ2 and putative thiamine synthase, appeared to interact with XopNKXO85 in yeast. This interaction was further confirmed by bimolecular fluorescence complementation and in vivo pull-down assays. OsVOZ2 is a hypothetical protein, and OsXNP is a putative thiamine synthase. To investigate roles of OsVOZ2 in interactions between rice and Xoo, I evaluated virulence of the wild-type and the xopNKXO85 mutant strain in the OsVOZ2 mutant rice generated by T-DNA insertion in Dongjin. Both the wild-type and the xopNKXO85 mutant were less virulent in the mutant rice than in the wild-type rice. Therefore, XopNKXO85 is a virulence factor that it plays an important role in the Xoo and rice interactions.