Red and blue light treatments of ripening bilberry fruits reveal differences in signaling through ABA regulated anthocyanin biosynthesis

The biosynthesis of anthocyanins has been shown to be influenced by light quality. However, the molecular mechanisms underlying the light-mediated regulation of fruit anthocyanin biosynthesis are not well understood. In this study, we analyzed the effects of supplemental red and blue light on the anthocyanin biosynthesis in non-climacteric bilberry (Vaccinium myrtillus L.). After six days of continuous irradiation during fruit ripening, both red and blue light elevated concentration of total anthocyanins, but especially red light promoted accumulation of delphinidins. Transcriptomic analysis of ripening berries showed that both light treatments up-regulated all the major anthocyanin structural genes, the key regulatory MYB transcription factors and abscisic acid (ABA) biosynthetic genes. However, higher induction of specific genes of anthocyanin and delphinidin biosynthesis alongside ABA signal perception and metabolism were found in red light. The difference in red and blue light signaling was found in NCED, ABA receptor PYL and catabolic ABA-8’hydroxylase gene expression. Red light also up-regulated expression of SNARE domain transporters, which may indicate involvement of these proteins in vesicular trafficking of anthocyanins during fruit ripening. Our results suggest differential signal transduction and transport mechanisms between red and blue light in in ABA- regulated anthocyanin and delphinidin biosynthesis during non-climacteric fruit ripening.