Abstract
Anthocyanins contribute to most colors of plants and play protective roles in response to abiotic stresses. Brassica napus is widely cultivated worldwide as both an oilseed and a vegetable. However, only several high anthocyanin-containing cultivars have been reported, and the mechanisms of anthocyanin accumulation have not been well-elucidated in B. napus. Here, the phenotype, comparative whole-genome identification, and gene expression analysis were performed to investigate the dynamic change of the anthocyanin content and the gene expression patterns of anthocyanin biosynthetic genes (ABGs) in B. napus. A total of 152 ABGs were identified in the B. napus reference genome. To screen out the critical genes involved in anthocyanin biosynthesis and accumulation, the RNA-seq of young leaves of two B. napus lines with purple leaves (PL) or green leaves (GL), and their F1 progeny at 41, 91, and 101 days were performed to identify the differentially expressed genes. The comparative expression analysis of these ABGs indicated that the upregulation of TT8 together with its target genes (such as DFR, ANS, UFGT, and TT19) might promote the anthocyanin accumulation in PL at the early developmental stage (41–91 days). While the downregulation of those ABGs and anthocyanin degradation at the late developmental stage (91–101 days) might result in the decrease in anthocyanin accumulation. Our results would enhance the understanding of the regulatory network of anthocyanin dynamic accumulation in B. napus.
Highlights
Anthocyanins are a class of natural pigments responsible for the orange, red to purple, and blue colors of many fruits and vegetables (Buer et al, 2010)
The early biosynthetic genes (EBGs) are regulated by a class of R2R3–MYB transcription factors, while the regulation of late biosynthetic genes (LBGs) requires a ternary complex of MYB–bHLH–WD40 (MBWs), which binds the promoters of target genes and activate their transcription, leading to a higher accumulation of the anthocyanin level (Lepiniec et al, 2006; Xu et al, 2014; Kim et al, 2017)
The average anthocyanin contents in purple leaves (PL) (1.09 mg/kg DW) were about 3.9-fold higher than those in green leaves (GL) (0.28 mg/kg DW, p < 0.05, paired Students’ t-test), they varied at different developmental stages in the leaves of PL (Figure 1F)
Summary
Anthocyanins are a class of natural pigments responsible for the orange, red to purple, and blue colors of many fruits and vegetables (Buer et al, 2010). The EBGs are regulated by a class of R2R3–MYB transcription factors, while the regulation of LBGs requires a ternary complex of MYB–bHLH–WD40 (MBWs), which binds the promoters of target genes and activate their transcription, leading to a higher accumulation of the anthocyanin level (Lepiniec et al, 2006; Xu et al, 2014; Kim et al, 2017). The overexpression of BjTT8 and its target genes which are involved in late anthocyanin biosynthesis and transport, account for the increasing levels of anthocyanin accumulation in purple leaves of B. juncea (Mushtaq et al, 2016; Heng et al, 2020b; Zhang et al, 2020). It has been demonstrated that some environmental factors, such as light or temperature, could influence anthocyanin accumulation by modulating the expression of ABGs (Nguyen et al, 2015; Kim et al, 2017)
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