Abstract
Chinese cabbage (Brassica rapa) is a major vegetable crop in China. The accumulation of anthocyanins improves the quality and flavor of Brassica crops and is beneficial for human health. There has been great research interest in breeding purple Chinese cabbage, for which it is necessary to study the key genes and mechanisms of anthocyanin accumulation. Through distant hybridization between purple mustard (Brassica juncea) and green Chinese cabbage (B. rapa), purple Chinese cabbage plants were obtained. Furthermore, the Dark_Pur gene was cloned in the purple Chinese cabbage plants, which came from purple mustard and may be responsible for the purple phenotype in purple Chinese cabbage plants. Through particle bombardment of isolated microspores from Chinese cabbage to transform the Dark_Pur gene, the transformed purple Chinese cabbage plant was obtained, thus verifying the function of the Dark_Pur gene. To further study the Dark_Pur gene regulatory mechanism of anthocyanin accumulation in Chinese cabbage, the purple/green Chinese cabbage lines and purple/green mustard lines were subjected to transcriptome–metabolome analysis. Three stages (cotyledon, seedling, and large-leaf stages) of the purple/green Chinese cabbage lines and purple/green mustard lines were selected for analysis. The results indicated that the expression level of the transcription factor genes BraA09g028560.3C, BraA03g019460.3C, and BraA07g035710.3C may be induced by the Dark_Pur gene and they play an important role in purple Chinese cabbage, and BjuB010898 and BjuO006089 may be responsible for anthocyanin accumulation in mustard. Studying the structural genes of the purple Chinese cabbage showed that PAL, C4H, 4CL, CHS, CHI, F3H, F3’H, FLS, DFR, ANS, and UGT were up-regulated in three growth periods. There were 22 and 10 differentially expressed metabolites (DEMs) in seedling and large-leaf stages between purple/green Chinese cabbage, respectively, and 12 and 14 differentially expressed metabolites (DEMs) in seedling and large-leaf stages between purple/green mustard, respectively, which may indicate that the Dark_Pur gene from purple mustard greatly regulates anthocyanin accumulation in purple Chinese cabbage. This study provides a foundation for further elucidating anthocyanin regulation.
Highlights
Anthocyanins are flavonoids and important water-soluble pigments that make up the color of plants
Some studies show that late biosynthetic genes (LBGs) are regulated by the MBW complex, which consists of MYB, bHLH, and WD40 transcription factors, and early biosynthetic genes (EBGs) are usually activated by the R2R3-MYB transcription factor [14,15]
In Arabidopsis, the AtPAP1, AtMYB113, AtMYB114, AtTT8, and AtTTG1 genes may participate in MBW formation [6]
Summary
Anthocyanins are flavonoids and important water-soluble pigments that make up the color of plants. The mechanisms of anthocyanin biosynthesis and regulation in model species such as Arabidopsis, Zea mays, and Petunia hybrida have been well studied [6,7]. Overexpression of AtPAP1, AtMYB113, and AtMYB114 can increase the production of anthocyanin in a TTG1- and bHLH-cooperative manner, and the TT2, TT8, and TTG1 genes can activate proanthocyanin biosynthesis in Arabidopsis seeds [16,17]. MYBL2 and CPC, and LBD37, LBD38, and LBD39 are negative regulators of anthocyanin biosynthesis in Arabidopsis [18,19]. The key regulatory genes AtPAP1 and AtPAP2 were suppressed by the negative regulators AtLBD37, AtLBD38, and AtLBD39 in anthocyanin biosynthesis in Arabidopsis [19,21]. Previous findings suggest that both activators and repressors are important in the anthocyanin biosynthesis pathway
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