Bhendi yellow vein mosaic virus C4 circumvents the RNA silencing pathway by interacting with SAM synthetase and cystathionine beta synthase

Abstract

Post-transcriptional and transcriptional gene silencing represents critical innate antiviral defense mechanisms in plants. Viruses encode clusters of viral silencing suppressors to infect plants to counteract the plant's antiviral response effectively. Previous studies have identified Bhendi yellow vein mosaic virus (BYVMV) C4 and C2 proteins as post-transcriptional gene silencing (PTGS) and transcriptional gene silencing (TGS) suppressors, yet the underlying mechanisms of action remain elusive. In our current research, we reveal that the BYVMV C4 protein interacts with S-adenosyl methionine synthetase (SAMS) and cystathionine β-synthase (CBS), both of which play crucial roles in the methyl cycle, either directly or indirectly, thus inhibiting the S-adenosylmethionine (SAM) cycle. Silencing of CBS and SAMS through virus-induced gene silencing (VIGS) resulted in increased symptom susceptibility, elevated viral DNA accumulation, and decreased cytosine methylation on the BYVMV promoter. These findings indicate that BYVMV C4 suppresses PTGS and TGS by inhibiting SAMS and CBS activity, thereby enhancing plant viral infection.