Metabolomics integrated with transcriptomics provides insights into the phenylpropanoids biosynthesis pathway in Lilium davidii var. unicolor and L. lancifolium Thunb

Lilium spp. is a world-famous bulbous flower with outstanding ornamental, edible, and medicinal value. Evaluating the taste of edible lilies and identifying important active substances and genes are necessary for germplasm improvement, new variety breeding, and industrial application. To better understand the phenylpropanoids and regalosides biosynthesis, L. davidii var. unicolor and L. lancifolium Thunb. bulbs were used for transcriptome and metabolite analysis. Results showed that the phenols and flavonoid contents in JT were lower than in LT, while the saponins and alkaloid contents in JT were higher than in LT. A total of 20,520 differentially expressed genes (DEGs) and 383 differential metabolites were searched. Integrated transcriptomics and metabolomics analysis showed that phenylpropanoid biosynthesis and flavonoid biosynthesis were differentially altered. Ninety-nine unigenes encoding ten phenolic acids and two flavonoids were identified as candidate genes involved in phenylpropanoid and flavonoid biosynthesis. WGCNA analysis showed 76 phenylpropanoid and flavonoid biosynthesis-related unigenes were verified as likely to be involved in phenylpropanoid metabolism and regalosides accumulation. Among them, 15 genes were used for qRT-PCR, and four genes were utilized for tissue-specific expression pattern analysis. Down-regulation of LdPAL2 and LdC4H1 in bulbs of L. davidii var. unicolor via virus induced gene silence (VIGS) reduced the contents of p-coumaric acid and cinnamic acid. These results contribute to understanding phenylpropanoid metabolism and identifying potential functional genes for improving the regalosides and flavonoids content in Lilium bulbs.