Transcriptomic and Metabolomic Profiling Provides Insights into Flavonoids Biosynthesis and Flower Coloring in Loropetalum chinense and Loropetalum chinense var. rubrum

The Loropetalum chinense and Loropetalum chinense var. rubrum are typical and traditional ornamental and Chinese herbal medicine in Asia. However, more information is needed on the mechanisms underlying its flower coloring. Here, we profiled the flavonoid metabolome, full-length sequencing, and transcriptome analysis to investigate the flavonoid biosynthesis and global transcriptome changes among different petal coloring cultivars of L. chinense and L. chinense var. rubrum. The total anthocyanins and phenotypic of the petal were highly consistent with the petal color. Moreover, a total of 207 flavonoid components were identified. Of these, 12 flavonoid components were considered significantly different expression compounds among the four samples. Meanwhile, the first reference full-length transcriptome of L. chinense var. rubrum was being built, which had 171,783 high-quality non-redundant transcripts with correcting with next-generation sequencing (NGS). Among them, 52,851 transcripts were annotated in the seven database of NR, KOG, GO, NT, Pfam, Swiss-Port and KEGG. Combined with NGS analysis, the DETs involved in flavonoids and anthocyanins contributed greatest to the flower-coloring. Additionally, the different expressed of eight LcDFRs and four LcANS genes were positively correlated with flavonoid biosynthesis, and the four LcBZ1 and one Lc3Mat1 were positively correlated with the content of seven anthocyanins revealed by coupling with metabolomics and transcriptomics analysis. Together these results were used to mine candidate genes by analyzing flower coloring changes in a comprehensive metabolic and transcriptomic level in L. chinense and L. chinense var. rubrum.