Integration of full-length transcriptomes and anthocyanin metabolite analysis for understanding fruit coloration mechanism in Schisandra chinensis

Coloration directly affects the commercial value of Schisandra chinensis fruits. The composition and content of anthocyanin determine the S. chinensis fruit coloration. However, the molecular mechanism of anthocyanin biosynthesis and regulation in this fruit remains unknown. In this study, we performed integrative full-length transcriptomics and targeted metabolomics analyses in S. chinensis fruits at four different developmental stages to elucidate the coloration mechanism. Cyanidin3- O -xyl-rutinoside is the key anthocyanin, which is responsible for the reddening of S. chinensis fruits, and its accumulation gradually accelerated from the 80th day after fluorescence. Overall, 122,289 unigenes with an average length of 2592 bp and an N50 of 4232 bp were obtained through single-molecule real-time sequencing; a total of 16,456 differentially expressed genes were identified. Moreover, 10 full-length structural genes related to anthocyanin biosynthesis were found to be significantly differentially expressed with fruit ripening. Moreover, 10 glycosyltransferases (GTs) that may possess the activities of anthocyanidin 3- O -glucosyltransferase, anthocyanidin 3- O -glucoside rhamnosyltransferase, and xylosyltransferases, which are involved in the final three steps for cyanidin3- O -xyl-rutinoside synthesis, were identified through phylogenetic analysis. Based on these findings, we constructed the complete anthocyanin biosynthetic pathway in S. chinensis fruits; five ScMYB s, three ScbHLH s, and two ScWD40 s potentially involved in regulating anthocyanin biosynthesis in S. chinensis fruits were also selected. Our study provides the foundation for further research on the molecular mechanism of anthocyanin biosynthesis and regulation for improving the quality of S. chinensis fruits. The results of full-length transcriptomes would provide researchers with novel insights into the molecular cloning of enzymes and their activity.