Metabolomics Combined with Transcriptomics Analysis Reveals the Regulation of Flavonoids in the Leaf Color Change of Acer truncatum Bunge

The color variation of the leaves in autumn is a significant ornamental feature of <i>Acer truncatum</i> Bunge, especially when the leaves gradually become redder. Many studies focused on leaf color changes; however, less research has been conducted on the mechanism by which <i>A. truncatum</i>'s autumn leaves turn red. Red, middle and green leaves of <i>Acer truncatum</i> were used as the study materials to evaluate their flavonoid-related metabolites and infer gene and metabolite expression patterns in conjunction with transcriptome expression. For a start, phenotypic and leaf color parameters analyses showed that red leaves had the highest color redness and greenness (a*). In addition, a total of 23 flavonoid-related metabolites were identified through the metabolome, including five anthocyanins. Of them, cyanidin 3-O-β-D-sambubioside, cyanidin 3-O rutinoside, pelargonidin 3-O-3″,6″-O-dimalonylglucoside, delphinidin 3,7-di-O-β-D-glucoside and 3-O-β-D-sambubioside would help the leaves turn red in <i>A. truncatum</i>. Similarly, combined transcriptomics and metabolomics analyses showed that most genes in the flavonoid and anthocyanin biosynthetic pathways were differentially expressed in both types of leaves. Chalcone synthase (<i>CHS</i>), dihydroflavonol 4-reductase (<i>DFR</i>) and anthocyanin synthase (<i>ANS</i>) could affect flavonoid synthesis during leaf color change. This study could provide data for the genetic improvement of maple plants by exploring valuable metabolites and genes in flavonoid synthesis, and enhance the understanding of different developmental stages.