Abstract
Soybean sprouts are a flavorful microgreen that can be eaten all year round and are widely favored in Southeast Asia. In this study, the regulatory mechanism of calcium on anthocyanin biosynthesis in soybean sprouts under blue light was investigated. The results showed that blue light, with a short wavelength, effectively induced anthocyanin accumulation in the hypocotyl of soybean sprout cultivar “Dongnong 690.” Calcium supplementation further enhanced anthocyanin content, which was obviously inhibited by LaCl3 and neomycin treatment. Moreover, exogenous calcium changed the metabolism of anthocyanins, and seven anthocyanin compounds were detected. The trend of calcium fluorescence intensity in hypocotyl cells, as well as that of the inositol 1,4,5-trisphosphate and calmodulin content, was consistent with that of anthocyanins content. Specific spatial distribution patterns of calcium antimonate precipitation were observed in the ultrastructure of hypocotyl cells under different conditions. Furthermore, calcium application upregulated the expression of genes related to anthocyanin biosynthesis, and calcium inhibitors suppressed these genes. Finally, transcriptomics was performed to gain global insights into the molecular regulation mechanism of calcium-associated anthocyanin production. Genes from the flavonoid biosynthesis pathway were distinctly enriched among the differentially expressed genes, and weighted gene co-expression network analysis showed that two MYBs were related to the accumulation of anthocyanins. These results indicated that calcium released from apoplast and intracellular stores in specific spatial-temporal features promote blue light-induced anthocyanin accumulation by upregulation of the expression of genes related to anthocyanin synthesis of “Dongnong 690” hypocotyl. The findings deepen the understanding of the calcium regulation mechanism of blue light-induced anthocyanin accumulation in soybean sprouts, which will help growers produce high-quality foods beneficial for human health.
Highlights
Anthocyanins, derived from the metabolic pathway of phenylpropane, are important nutritional components of fruits and vegetables
With continuous light exposure of up to 36 h, the total anthocyanin content (TAC) in B was further enhanced, but it did not significantly fluctuate in W (Figure 1B). These results indicate that blue light is more effective than white light in inducing the accumulation of anthocyanins in “Dongnong 690” hypocotyls
The application of LaCl3 and neomycin obviously weakened the positive effects of calcium on TAC throughout the experiment
Summary
Anthocyanins, derived from the metabolic pathway of phenylpropane, are important nutritional components of fruits and vegetables. The visible color imparted by anthocyanins attracts pollinators to promote plant reproduction (Andersen and Markham, 2005). The mechanism of anthocyanin biosynthesis has been clearly elucidated in many species (Almeida et al, 2007). Some structural genes are usually regulated by members of the MBW complex, composed of the R2R3-MYB transcription factor, basic helix-lool-helix (bHLH), and WD repeat domain containing proteins (WD40). MdMYB308L physically interacts with MdbHLH33 and enhances its binding to the MdDFR promoter to improve anthocyanin accumulation in apple (An et al, 2020). Few MYBs are involved in the inhibition of anthocyanin biosynthesis. Members of MBW synergistically regulate anthocyanin biosynthesis by interacting with other transcription factors, such as COP1, NAC, and WRKY (Zhou et al, 2015)
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