Rapeseed’s (Brassica napus L.) colorful petals have important ornamental values. However, the mechanisms of regulating petals coloration in rapeseed are still unknown. In our study, we investigated the key differential coloring substances in nine rapeseed cultivars with different petal colors, and 543 metabolites were detected and characterized through UPLC-HESI-MS/MS. Among them, the kinds and contents of flavonols, flavones, and anthocyanidins were the main contributors to petals’ coloration. Tamarixetin-, quercetin-, butin-, naringenin- and luteolin-derivates were the main pigment bases in white and yellow petals. Peonidin-3,5-O-diglucoside, peonidin-3-O-(6″-O-caffeoyl)glucoside, and quercetin-derivatives were the main coloring substances in pink petals. Acylated cyanidin derivatives might lead to a series of different purple petal colors. Glycosylated anthocyanins were responsible for the coloration of rapeseed red petals, and peonidin-3-O-glucoside and kaempferol-derivatives were mainly detected from the red petals. These results provide comprehensive insights into the difference in flavonoid metabolites in rapeseed petals with different colors and supply theoretical supports for the breeding of novel colorful rapeseed cultivars.

Background The colorful rapeseed petals have specific phenotype and excellent ornamental value. However, the coloration mechanism of rapeseed petals are poorly understood. In this study, the integrative metabolome and transcriptome analysis of white, yellow, dark purple, and dark red rapeseed petals were analyzed to elucidate the mechanisms regulating petal pigmentation. Results The metabolome analysis results revealed that chalcones compounds, tamarixetin-3-O-glucoside-7-O-rhamnoside and 4'-hydroxy-2,4,6-trimethoxydihydrochalcone diaplayed a higher accumulation in the yellow color of rape petals, acylated anthocyanins, cyanidin-3-O- (6"-O-caffeoyl) sophoroside-7-O-glucoside and cyanidin-3-O-feruloylglucoside-5-O-glucoside were the main pigments that caused the dark purple color of rapeseed petals, and glycosylated anthocyanins, peonidin-3-O-glucoside were the main coloring substances in the dark red rape petals. KEGG and qRT-PCR results suggested that the higher expression of CHS lead to the accumulation of 4'-hydroxy-2,4,6-trimethoxydihydrochalcone in yellow petals. ANS1, CCoAAT2 and CCoAOMT were responsible for regulating the biosynthesis of cyanidin-3-O- (6"-O-caffeoyl) sophoroside-7-O-glucoside and cyanidin-3-O-feruloylglucoside-5-O-glucoside in dark purple petals. ANS1, UGT, MT1, and MT2 co-expressed to regulate peonidin-3-O-glucoside content in dark red petals. The differential expression of CHS, ANS, UGT, CCoAOMT, CCoAAT2, and MT2 was contributed to the yellow, dark purple and dark red formation of rapeseed flowers. Through weighted gene co-expression network analysis, it was found that five modules were highly correlated with flavonoids accumulation, in which five candidate transcription factors MYB12, MYB122, MYB114, bHLH21, and bHLH96 related to flavonoids biosynthesis were identified. Conclusion A genetic and metabolic regulatory network of flavonoid biosynthesis in rapeseed petals with different color was proposed, according to the those differential flavonoids and the candidate genes screened. In summary, this study elucidated the molecular mechanism of coloration formation in rapeseed petal for comprehensive utilization.