Pathogen effector proteins are delivered to host cells to suppress plant immunity. However, the mechanisms by which effector proteins function are largely unknown. Here we show that expression of XopP Xoo , an effector of rice pathogen Xanthomonas oryzae pv. oryzae, in rice strongly suppresses peptidoglycan (PGN)-and chitin-triggered immunity and resistance to X. oryzae. XopP Xoo targets OsPUB44, a rice ubiquitin E3 ligase with a unique U-box domain. We find that XopP Xoo directly interacts with the OsPUB44 U-box domain and inhibits ligase activity. Two amino-acid residues specific for the OsPUB44 U-box domain are identified, which are responsible for the interaction with XopP Xoo . Silencing of OsPUB44 suppresses PGN-and chitin-triggered immunity and X. oryzae resistance, indicating that OsPUB44 positively regulates immune responses. Thus, it is likely that XopP Xoo suppresses immune responses by directly interacting with and inhibiting a positive regulator of plant immunity.

Bacillus strains JCM 19045, JCM 19046, and JCM 19047 are alkaliphiles that produce β-cyclodextrin from starch. They are related to Bacillus xiaoxiensis and Bacillus lehensis. The genome information for these three strains will be useful for studies of the physiological role of cyclodextrin and cyclodextrin production.