Effects of Shading on the Synthesis of Volatile Organic Compounds in ‘Marselan’ Grape Berries (Vitis vinifera L.)

Light is a vital environmental factor that can affect the synthesis of volatile organic compounds (VOCs) in grape berries. However, the mechanism through which light affects the synthesis of VOCs is still unclear for wine grapes. In our study, fruit bags with light transmittances of 50%, 15%, 5%, and 0% were used to bag the ‘Marselan’ clusters 45 days after flowering, and these treatments were named A, B, C, and D, respectively. The non-bagged clusters were used as controls (CK). The types and contents of VOCs were determined using a gas chromatography–mass spectrometer (GC–MS) with the berries 35 days before harvest (S1), 25 days before harvest (S2), and at the harvest stage (S3). RNA-seq analysis was performed on S2 and S3 samples. The results showed that the types and total contents of VOCs synthesized by fatty acid metabolic and isoprene metabolic pathways decreased with a decrease in light intensity in berries at S3. The types of VOCs synthesized by the amino acid metabolic pathway were reduced under complete shading conditions, which was consistent with results of other treatments and in the CK. The total content of VOCs was significantly reduced in shaded berries. The components of VOCs were also significantly decreased in shaded berries, except for 2-heptanol, cis-7-decenal, and trans-2-hexenal. Furthermore, RNA-seq analysis revealed that the pathway related to VOC synthesis was the alpha-linolenic acid metabolic pathway, which contained 10 differentially expressed genes from the LOXO , HPL , and ADH gene families. Correlation analysis between metabolites and differentially expressed genes of this pathway showed that the synthesis of most VOCs was highly correlated with the expression levels of LOXOs (VIT_09s0002g01080, VIT_06s0004g01450), HPL (VIT_12s0059g01060), and ADHs (VIT_04s0044g01110, VIT_18s0001g15450, VIT_18s0001g15410) ( r > 0.95, p 0.95, p