The involvement of PybZIPa in light-induced anthocyanin accumulation via the activation of PyUFGT through binding to tandem G-boxes in its promoter

Abstract

To gain insight into how anthocyanin biosynthesis is controlled by light in fruit, transcriptome and metabolome analyses were performed in the Chinese sand pear cultivar "Mantianhong" (<i>Pyrus pyrifolia</i>) after bagging and bag removal. We investigated transcriptional and metabolic changes and gene-metabolite correlation networks. Correlation tests of anthocyanin content and transcriptional changes revealed that 1,530 transcripts were strongly correlated with 15 anthocyanin derivatives (<i>R</i> ² > 0.9, <i>P</i>-value < 0.05), with the top 130 transcripts categorized as being associated with flavonoid metabolism, transcriptional regulation, and light signaling. The connection network revealed a new photosensitive transcription factor, <i>PybZIPa</i>, that might play an important role during light-induced anthocyanin accumulation. The overexpression of <i>PybZIPa</i> promoted anthocyanin accumulation in pear and strawberry fruit as well as tobacco leaves. Dual luciferase and Y1H assays further verified that PybZIPa directly activated the expression of <i>PyUFGT</i> by binding to tandem G-box motifs in the promoter, which was key to differential anthocyanin accumulation in debagged pear skin, and the number of G-box motifs affected the transcriptional activation of <i>PyUFGT</i> by <i>PybZIPa</i>. The results indicate that the light-induced anthocyanin biosynthesis regulatory mechanism in pear differs from that described in previous reports suggesting that a <i>bZIP</i> family member co-regulates anthocyanin biosynthesis with other transcription factors in apple and <i>Arabidopsis</i>. It was found that, in response to light, <i>PybZIPa</i> promoted anthocyanin biosynthesis by regulating important transcription factors (<i>PyMYB114</i>, <i>PyMYB10</i>, and <i>PyBBX22</i>) as well as structural genes (<i>PyUFGT</i>) via binding to G-boxes within promoters. This activation was amplified by the self-binding of <i>PybZIPa</i> to activate its own promoter. Overall, we demonstrate the utility of a multiomics integrative approach for discovering new functional genes and pathways underlying light-induced anthocyanin biosynthesis.