Light affects anthocyanin biosynthesis via transcriptional regulation of COP1 in the ever-red leaves of crabapple M.cv. ‘Royalty’

The rare ever-red crabapple ( Malus spp.) leaves have importantly ornamental and medicinal traits, and their coloration is regulated by light conditions. However, little is known about the molecular mechanism of the red color formation via anthocyanin biosynthesis mediated by upstream regulators of light signaling under different light conditions. We selected the ever-red leaf cultivar, M.cv. ‘Royalty,’ to investigate the expression profile of various factors under dark conditions. The factors studied include the photoreceptors McphyA and McphyB , the ubiquitin E3 ligase McCOP1 , the transcription factor McMYB10 , the MBW complex, the main structural genes in anthocyanin biosynthesis, and the photomorphogenesis transcription factors McbZIP and McHY5 . Our results indicated that under dark conditions McCOP1 expression was up-regulated, while the expression of other factors studied was down-regulated, leading to decreased expression of the structural genes involved in anthocyanin biosynthesis and reduction in anthocyanin content. Interestingly, when McCOP1 was silenced in the leaves, the expression of McMYB10 , McbHLH , McWD40 , McbZIP , and McHY5 was markedly up-regulated, resulting in the up-regulation of the structural genes including McF3H , McFLS , McDFR , and McUFGT and the subsequent accumulation of anthocyanins compared with leaves treated with empty vector. These data demonstrate that darkness negatively regulates the coloration of the ever-red leaves by regulating McCOP1 expression, further inhibiting the expression of McMYB10 and the structural genes in anthocyanin biosynthesis. These results may provide important insight into the breeding of color-leafed plants.