A virulence protein activates SERK4 and degrades RNA polymerase IV protein to suppress rice anti-viral immunity

We have recently shown that the virulence protein P3 of rice grassy stunt virus promotes pathogenesis by inducing proteasome-controlled degradation of the rice RNA polymerase IV protein NRPD1a controlled by the P3-interacting E3 ubiquitin ligase P3IP1. However, the underlying mechanisms remain elusive.

In this study, we show that P3 acts as a virus-encoded transcription activator-like effector to upregulate transcription of Somatic Embryogenesis Receptor Kinase 4 (SERK4) by directly binding to its promoter. SERK4 phosphorylates P3IP1 and enhances Pol IVa (NRPD1a) degradation following P3IP1-controlled ubiquitination, leading to attenuated antiviral defense in rice. Thus, our study finds a critical viral virulence strategy by encoding a transcription factor-like protein that activates a host kinase to promote proteasome- controlled degradation of NRPD1a, thereby disarming RNA-directed DNA methylation (RdDM) antiviral defense.