Antiviral RNA interference in plants: Increasing complexity and integration with other biological processes.

RNA interference (RNAi, also known as RNA silencing) is one of the most important plant defense responses against viral invasion. Although major components of the RNAi pathway, steps leading to viral small interfering RNA biogenesis, and viral counterdefense strategies via RNAi suppressors have been well studied, the broader roles of RNAi in viral infection and seed transmission remain less thoroughly characterized. In particular, the increasing complexity of RNAi-associated mechanisms and their integration with other biological processes have not been comprehensively summarized. Increasing numbers of studies have identified non-canonical RNAi pathways, novel host factors involved in RNAi, and the possibility of small RNAs acting across kingdoms to modulate plant-virus-vector tritrophic interactions. In this review, we provide an overview of the roles of RNAi in plant viral infections and describe recent advances, with emphasis on the discoveries of novel positive and negative RNAi regulators, potential signaling pathways upstream and downstream of antiviral RNAi, and the prospects and challenges of double-stranded RNA applications, either expressed from transgenes or supplied exogenously via spraying. We also discuss how these findings reshape current views on antiviral RNAi, highlight remaining knowledge gaps, and examine how these advances influence plant-virus co-evolution while informing strategies for managing plant virus diseases and reducing their impact.