Integrated metabolomic and transcriptomic analyses reveal that bagging delays ripening of ‘Ruidu Kemei’ grape berries

Abstract

‘Ruidu kemei’ (Kemei) is a new variety of rose-scented grape that was selected from among the hybrid offspring of ‘Italy’ × ‘Muscat Louis’. Bagging is a common technical measure that is used to improve fruit quality during production, but the potential influence of bagging on the quality of Kemei grapes is not clear. To uncover the mechanism by which bagging may affect Kemei quality formation, we analyzed physiological, transcriptomic, and metabolomic data from Kemei fruits at several stages of growth under either bagged conditions or natural light as a control. The results showed that bagging increased the total soluble solid (TSS) content and the sugar-acid ratio in Kemei grapes, but had no significant effect on titratable acid (TA) levels at the over-mature period. However, TSS levels decreased in over-ripe Kemei grapes grown under natural light, suggesting that bagging inhibited Kemei fruit growth and delayed ripening. Metabolomic analysis (GC–MS and LC-MS) revealed 295 differentially accumulated metabolites (DAMs) at the mature period in response to bagging treatment. RNA sequencing analysis (RNA-seq) identified 1535, 2568, and 2683 differentially expressed genes (DEGs) between bagged and natural-light samples at three different developmental stages. Further correlation analysis of DAMs and DEGs showed that 38 DEGs were related to starch and sucrose metabolic pathways, 22 were related to glycolysis, and five were related to the tricarboxylic acid (TCA) cycle. Taken together, these results contribute to a full understanding of the molecular and metabolic bases by which fruit bagging affects Kemei grape quality formation.