Viral Suppressors of RNA Silencing in Vegetable Viruses: Mechanism and Diversity
摘要
RNA silencing is a fundamental antiviral defense in plants, comprising processes that detect viral double-stranded RNA (dsRNA), process it into small interfering RNAs (siRNAs) via Dicer-like enzymes, and direct degradation or translational repression of viral mRNAs through Argonaute (AGO)-containing effector complexes. Vegetable-infecting viruses encounter the host defense system, and many have evolved viral suppressors of RNA silencing (VSRs) to circumvent RNA silencing at various levels. In this chapter, we examine the diversity of VSRs in vegetable viruses (e.g., those infecting Solanaceae, Cucurbitaceae, Brassicaceae) and dissect their molecular mechanisms. VSRs operate via multiple strategies: sequestering dsRNA or siRNAs to prevent their detection or loading into RISC; degrading or destabilizing key components such as AGO proteins; interfering with the amplification of the silencing signal (e.g., through RNA-dependent RNA polymerases (RdRPs) and Suppressor of Gene Silencing 3 (SGS3); blocking systemic spread of silencing signals; and even modulating endogenous small RNAs and microRNAs to perturb host gene regulation. These suppressors are structurally and evolutionarily diverse, often unrelated in sequence, and sometimes multifunctional, including serving roles in pathogenicity, movement, or symptom development in addition to silencing suppression. Understanding the mechanisms and diversity of VSRs in vegetable viruses has both theoretical and practical implications: it illuminates the arms-race dynamics between host and pathogen, aids in predicting viral virulence, and suggests approaches for resistance breeding or silencing-based antiviral strategies. Future work should aim to characterize lesser-known VSRs in emerging vegetable viruses, map precise host targets, and explore how VSRs affect plant development and immunity.