Cotton Leaf Curl Multan Virus C4 Protein Suppresses Both Transcriptional and Post-transcriptional Gene Silencing by Interacting with SAM Synthetase

Ismayil, A., Haxim, Y., Wang, Y., Li, H., Qian, L., Han, T., Chen, T., Jia, Q., Yihao Liu, A., Zhu, S., Deng, H., Gorovits, R., Hong, Yiguo, Hanley-Bowdoin, L. and Liu, Y. (2018) Cotton Leaf Curl Multan Virus C4 Protein Suppresses Both Transcriptional and Post-transcriptional Gene Silencing by Interacting with SAM Synthetase. PLOS Pathogens, 14 (8). e1007282.

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Abstract

Author summary Geminiviruses are single-stranded DNA (ssDNA) viruses that infect a wide range of plant species and are responsible for substantial crop damage worldwide. However, how geminiviruses inhibit plant antiviral gene silencing defense is unclear. Here, we report that a single geminiviral protein CLCuMuV C4 inhibits both plant transcriptional gene silencing (TGS) and post-transcriptional gene silencing (PTGS) to promote an effective viral infection. We show that CLCuMuV C4 protein interacts with SAMS, a core enzyme in methyl cycle, and inhibits SAMS activity. Overexpression of CLCuMuV C4 reduces the DNA methylation levels of both a transgene and an endogenous locus. Further, silencing of SAMS reduced both TGS and PTGS, and enhanced viral infection while CLCuMuV virus carrying a mutation in C4 that fails to interact with SAMS showed decreased infection. These findings reveal a novel mechanism by which the CLCuMuV C4 protein suppress SAMS mediated TGS and PTGS, leading to enhanced viral infection in plant.

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