Xanthomonas oryzae pv. oryzae type III effector PthXo3JXOV suppresses innate immunity, induces susceptibility and binds to multiple targets in rice

Transcription activator-like (TAL) effectors encoded by tal genes were recognized as a key virulence strategy used by Xanthomonas oryzae pv. oryzae (Xoo) to cause bacterial leaf blight of rice. TAL effector PthXo3 is a major virulence factor identified in a Philippine Xoo strain PXO61, and it can induce the expression of susceptibility gene OsSWEET14 by binding to the effector-binding element (EBE) in the promoter region. In this study, pthXo3 homologous genes were also identified and isolated from Xoo Chinese strain OS198 and Japanese strain JXOV, which were named as pthXo3OS198 and pthXo3JXOV, respectively. When pthXo3JXOV was delivered into PXO99A, the resulting strain PXO99A/pthXo3JXOV significantly increased virulence in 18 out of 23 rice varieties tested, with the most prominent increase in lesion length and bacteria propagation in rice IRBB13. PthXo3JXOV suppresses the plant's innate immunity by inhibiting hypersensitive response (HR) and callose deposition. The Agrobacterium tumefaciens-mediated transient expression assays showed that, besides OsSWEET14, PthXo3JXOV also interacts with other targets by binding to the EBEs in their promoter regions. Our results suggest that PthXo3JXOV may interact with multiple targets to execute its virulence functions.