Metabolome and transcriptome analysis predicts metabolism of violet-red color change in Lilium bulbs

During the storage and processing of Lilium bulbs, the phenomenon of violet-red colour change in Lilium bulbs which is different from enzymatic browning often exists, but the specific mechanism is not clear.

In this study, we chose six-year-old Lilium davidii var. unicolor to study. Bulb scales which were sealed in polyethylene film plastic bags were exposed to room temperature (20 ± 2 °C) treatment for 5 days (12 h of sunshine and 12 h of sun shading). Metabolomics and transcript omics were conducted to elucidate the mechanism of violet-red color change in Lilium bulbs. The results showed that the color of Lilium bulb scales was obvious violet-red in 5 days; chromaticity value measuring showed the a values had the most significant upward trend. Metabolomics analysis showed many metabolites produced from the flavonoid biosynthesis pathway showed an upward trend. Transcriptome revealed that flavonoid biosynthesis pathway was significantly enriched, of which 20 synthesis genes were highly regulated expression. Metabolome and transcriptome co-analysis that up-regulated expression of flavonoids synthesis genes including ten chalcone synthase, two anthocyanidin reductase, and chalcone isomerase, 3'-hydroxylase, 3-hydroxylase, dihydroflavonol 4-reductase, anthocyanin synthase, anthocyanidin 3-O-glucosyltransferase and flavonol synthase were highly positive correlated with epicatechin, rutin and cyanidin 3-rutinoside.

Phenotypic, metabolomic and transcriptomic analysis indicated that the up-related expression levels of genes and accumulated flavonoids related to flavonoid metabolism contributed greatly to the violet-red colour change in Lilium bulbs. The results of this study will deepen our understanding of the color formation of violet-red Lilium bulbs and provide the basis for future storage and preservation of Lilium bulbs. © 2021 Society of Chemical Industry.