Early molecular response of cold-deacclimated grapevine buds to late frost occurrences

Despite the observed increase of average global surface temperatures, spring frosts are expected to remain a threat to grapevine cultivation in several areas of the world. Due to higher vulnerability in proximity to budbreak, late freezing events can greatly damage bud vegetative and reproductive tissues thus affecting multiple years of production. Therefore, improving our understanding of the mechanisms underlying tolerance to unpredictable freezing events during cold deacclimation is of paramount importance to enhance grapevine’s resilience in a changing climate. A spring frost was registered, on April 7, 2021, in the Italian Region Friuli Venezia Giulia, allowing the field study of the early molecular responses of cold-deacclimated buds in the hybrid ‘Sauvignon Nepis’ (‘Sauvignon Blanc’ × ‘Bianca’), showing a good tolerance to this event. Results highlighted differential responses to late frost exposure depending on bud developmental stage, with the BBCH 00 stage (winter bud) being the most reactive. In particular, freezing tolerance-related genes (VvDHN1/2) and raffinose synthase encoding gene (VvRS) were upregulated in response to freezing shock. VvNCED1, involved in abscisic acid biosynthesis, and ethylene receptor VvEIN3 also appeared involved in this process. This work outlines several molecular pathways activated in cold-deacclimating buds in response to sudden frost occurrence and draws attention to the varying adaptation capabilities in relation to bud phenological stage.