Integrated Metabolomics and Transcriptomics Analyses Reveal Anthocyanin and Carotenoid Biosynthesis Involved in Color Development in Willow Bark

Shrub willow has strong adaptability, large biomass and short rotation period. Colorful willow barks have great ornamental and economic value. To study the color regulation mechanism, metabolomics and transcriptomics were used to analyze the purple, green and red barks. In the positive mode, a total of 1639 metabolites were identified and 1026 metabolites in negative mode. Flavone and flavonol biosynthesis (ko00944), flavonoid biosynthesis (ko00941), were all enriched in the 3 groups G vs P (G/P), G vs R (G/R) and P vs R (P/R). A total of 12 flavone and flavonol biosynthesis metabolites were isolated. A total of 448,839,796 raw reads were obtained with Q30 more than 93.15%. In the G/P, G/R and P/R groups, 27, 28 and 21 genes were enriched in the flavonoid biosynthesis (ko00941). The expression of CHS, ANS, DFR, ANR in the flavonoid biosynthesis pathway was the most in red. The content of canthaxanthin in purple bark was 10x more than green and 6x than red. The integration of metabolites and genes indicated the role of pelargonidin and canthaxanthin in regulating red and purple color pigment. Our research provides a fundamental basis for colorful willow breeding.