Single berry reconstitution prior to RNA-sequencing reveals novel insights into transcriptomic remodeling by leafroll virus infections in grapevines

Leafroll viruses are among the most devastating pathogens in viticulture and are responsible for major economic losses in the wine industry. However, the molecular interactions underlying the effects on fruit quality deterioration are not well understood. The few molecular studies conducted on berries from infected vines, associated quality decreases with the repression of key genes in sugar transport and anthocyanin biosynthesis. Sampling protocols in these studies did however not account for berry heterogeneity and potential virus induced phenological shifts, which could have biased the molecular information. In the present study, we adopted an innovative individual berry sampling protocol to produce homogeneous batches for RNA extraction, thereby circumventing berry heterogeneity and compensating for virus induced phenological shifts. This way a characterization of the transcriptomic modulation by viral infections was possible and explain why our results differ significantly from previously reported repression of anthocyanin biosynthesis and sugar metabolism. The present study provides new insights into the berry transcriptome modulation by leafroll infection, highlighting the virus induced upregulation of plant innate immunity as well as an increased responsiveness of the early ripening berry to biotic stressors. The study furthermore emphasizes the importance of sampling protocols in physiological studies on grapevine berry metabolism.