A three-way interplay between GLRaV-2, abiotic stress, and RNA silencing responses in grapevine

Winegrowers ever faced the dilemma of maintaining virus-infected vines that produce less grapes, or replacing them with virus-undetected plants, however at the cost of replanting and waiting years for a high-quality vintage. What decision should be made as now young plantings struggle to survive increasing abiotic threats due to climate change? Given that RNA silencing is a central antiviral defense mechanism, we investigated its responses to viral and abiotic threats and their combination. Climate variables, leaf temperature, viral titers, and transcript levels of 14 RNA-silencing genes were monitored over 7-years in 6 vineyards grown by different winegrowers. Proportions of GFLV, GLRaV1-3, GVA-infected vines, number and titer of infecting viruses per plant decreased under abiotic threats, eventually resulting in virus-undetected zones in apical meristems, which later developed into virus-undetected green shoots. At leaf temperatures below 30°C, RNA silencing transcripts levels increased as GLRaV-2 virus raised, thereby suggesting lack of RNA silencing suppression, at least beyond phloem, where this virus is confined. This was confirmed with GFP-fluorescence assays and molecular analysis. When leaf temperature raised above 30°C until 38.5°C, RNA silencing transcripts levels decreased in virus-undetected plants. In contrast, in GLRaV-2–infected vines, RNA silencing responses were reshaped. Transcript levels of VvRdR2, VvDCL1, VvDCL3, VvAGO1, VvAGO2, VvNPRD1, and VvHEN1, still increased in response to viral infection. Conversely, transcript levels of VvRdR1, VvRdR6, VvDCL2, VvDCL4, and VvSDE5 decreased. Overall, our findings show that combined abiotic and biotic stresses reshape RNA silencing machinery, potentially influencing vine resilience under challenging climate change.