Photosynthesis and fatty acid metabolism reveals the effects of shading treatment on the fruit aroma quality of cucumber (Cucumis sativus L.).

• The changes in the sugar, fatty acid, and aroma in cucumber fruits under shading treatment. • Transcriptomic revealed differences in flavor of cucumber under shading and unshading treatment. • The role of photosynthesis in regulating the formation of aldehydes and alcohols aroma of cucumber. The distinctive aroma of cucumber fruit is highly appreciated by consumers. The aroma of cucumber fruit is primarily influenced by the concentration of six- and nine-carbon aldehydes and their related alcohols, which are produced by metabolites of the lipoxygenase pathway. The formation of volatile aroma compounds in cucumber fruits is inseparable from plant photosynthesis, but the mechanism of light regulation of volatile compound synthesis is unclear. In this study, the effects of shading on aroma, undesirable flavours, sugars and fatty acids metabolisms in cucumber fruit were investigated. The results showed that (E)-2-Nonenal, (E, Z)-2,6-Nonadienal, and other aldehydes were significantly increased, while 1-Nonanol, 1-Hexanol, and other alcohols were significantly decreased, undesirable flavours dominated by (E)-2-Nonenal were strongly promoted to accumulate 1.56-fold in commercially ripe fruit under shading. Furthermore, the contents of sugars and fatty acids were decreased by 28 % and 12 % respectively. Transcriptomic analysis showed 35 differentially expressed genes in the biosynthesis and metabolism of fatty acids and lipoxygenase pathway in photosynthesis under shading were significantly down-regulated. Based on the comprehensive analysis of multi-omic data, it was shown light regulates the formation of volatile aroma substances in fruits by regulating the substrate level of the fatty acid metabolic pathway and the expression of related genes. [ABSTRACT FROM AUTHOR]