A viral small interfering RNA-host plant mRNA pathway modulates virus-induced drought tolerance by enhancing autophagy.

Virus-induced drought tolerance presents a fascinating facet of biotic-abiotic interaction in plants, yet its molecular intricacies remain unclear. Our study shows that cowpea mild mottle virus (CPMMV) infection enhances drought tolerance in common bean (Phaseolus vulgaris) plants through a virus-derived small interfering RNA (vsiRNA)-activated autophagy pathway. Specifically, a 21 nt vsiRNA originating from the CPMMV Triple Gene Block1 (TGB1) gene targeted the 5' untranslated region (UTR) of the host Teosinte branched 1, Cycloidea, Proliferating Cell Factor (TCP) transcription factor gene PvTCP2, independent of the known role of TGB1 as an RNA silencing suppressor. This targeting attenuated the expression of PvTCP2, which encodes a transcriptional repressor, and in turn upregulated the core autophagy-related gene (ATG) PvATG8c, leading to activated autophagy activity surpassing the level induced by drought or CPMMV infection alone. The downstream EARLY RESPONSIVE TO DEHYDRATION (ERD) effector PvERD15 is a homologue of Arabidopsis thaliana AtERD15, which positively regulates stomatal aperture. PvERD15 was degraded in PvATG8c-mediated autophagy. Therefore, we establish a TGB1-PvTCP2-PvATG8c-PvERD15 module as a trans-kingdom fine-tuning mechanism that contributes to virus-induced drought tolerance in plant-drought-virus interactions.