XopR TTSS-effector regulates in planta growth, virulence of Indian strain of Xanthomonas oryzae pv. oryzae via suppressing reactive oxygen species production and cell wall-associated rice immune responses during blight induction

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) causing bacterial blight of rice is a global problem in rice production. Phytopathogenic Xanthomonads overpower PAMP-triggered immunity (PTI) through secreting effectors via type III secretion system (TTSS). We previously screened the TTSS effector repository of an Indian strain of Xoo (race 4), a predominant strain from north-west India that contains 21 Xop and 18 TALE effectors. Here, we demonstrate that Xoo race 4 employs XopR for in planta colonisation, virulence and for the suppression of cell wall-associated immune responses in its natural host. XopR null mutant (Xoo ΔxopR) produced 2.6-fold less-severe lesion as compared with Xoo wild type. Xoo ΔxopR showed 1.58-fold reduced colonisation compared with wild indicating that XopR is required for maximum colonisation in rice. Xoo ΔxopR produced 3.8-fold more callose deposits compared with wild. Xoo ΔxopR caused significantly higher production of ROS in rice. RT-qPCR expression analysis of immune responsive genes of rice indicated 10- to 43-fold upregulation upon challenged inoculation with Xoo ΔxopR over wild. Altogether, our study revealed that XopR of Indian Xoo strain supports its in planta growth and contributes immensely for successful blight development through suppressing defence related events like reactive oxygen species production, callose deposition and transcript abundance of immune responsive genes during rice::Xoo interaction.