Individual berry sampling reveals novel transcriptomic modifications induced by leafroll virus infection in grapevine (V. vinifera) berries

Grapevine leafroll-associated virus (GLRaV) is one of the most widespread pathogens in viticulture and constitutes a major threat to the wine industry. However, poor information about the different molecular interactions underlying the phenotypic and physiological effects on its fruit are available. Only few molecular studies were conducted on berries from GLRaV infected vines in which the analysed berries were sampled at the same calendar day without accounting for intracluster berry heterogeneity and the potential phenological shifts induced by viral infection, which potentially masks important gene expression information. The present study emphasizes the importance of an innovative individual berry sampling protocol based on the sorting of the different berries according to their biochemical characteristics in order to mitigate the intra-cluster heterogeneity by reconstituting homogeneous batches for RNA extraction. This sampling strategy unveiled direct transcriptomic changes triggered by GLRaV infections that were mainly linked to auoimmune responses and not, as peviously reported to the repression of anthocyanin biosynthesis and sugar transport related genes. The results give new insights regarding the high sensitivity of the early ripening stage to GLRaV infections as well as the virus triggering of innate plant defence mechanism.