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

Abstract

The Loropetalum chinense and Loropetalum chinense var. rubrum are typical as well as traditional ornamental and Chinese herbal medicines in Asia; however, more information is needed on the mechanisms underlying their flower coloring. Here, we profiled the flavonoid metabolome and carried out full-length sequencing in addition to transcriptome analyses 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 in addition to the RHSCC values and CIE 1976 L*a*b* values of petals were highly consistent with petal color. Moreover, a total of 207 flavonoid components were identified. Of these, 13 flavonoid compounds were considered significantly different expression compounds highly consistent with color information in the 4 samples. Meanwhile, the first reference full-length transcriptome of L. chinense var. rubrum was built, which had 171,783 high-quality nonredundant transcripts with correcting with next-generation sequencing (NGS). Among them, 52,851 transcripts were annotated in the seven databases of NR, KOG, GO, NT, Pfam, Swiss-Port, and KEGG. Combined with NGS analyses, the DETs involved in flavonoids and anthocyanins contributed greatest to the flower coloring. Additionally, the different expressions of eight LcDFRs and four LcANS genes were positively correlated with flavonoid biosynthesis, and the four LcBZ1 as well as one Lc3Mat1 were positively correlated with the content of seven anthocyanins revealed by coupling with metabolomics and transcriptomics analyses. Together, these results were used to mine candidate genes by analyzing flower coloring changes at comprehensive metabolic and transcriptomic levels in L. chinense and L. chinense var. rubrum.