BBX16, a B‐box protein, positively regulates light‐induced anthocyanin accumulation by activating MYB10 in red pear

Summary The red coloration of pear ( Pyrus pyrifolia ) results from anthocyanin accumulation in the fruit peel. Light is required for anthocyanin biosynthesis in pear. A pear homolog of Arabidopsis thaliana BBX 22 , Pp BBX 16 , was differentially expressed after fruits were removed from bags and may be involved in anthocyanin biosynthesis. Here, the expression and function of Pp BBX 16 were analysed. Pp BBX 16 's expression was highly induced by white‐light irradiation, as was anthocyanin accumulation. Pp BBX 16 's ectopic expression in Arabidopsis increased anthocyanin biosynthesis in the hypocotyls and tops of flower stalks. Pp BBX 16 was localized in the nucleus and showed trans‐activity in yeast cells. Although Pp BBX 16 could not directly bind to the promoter of Pp MYB 10 or Pp CHS in yeast one‐hybrid assays, the complex of Pp BBX 16/Pp HY 5 strongly trans‐activated anthocyanin pathway genes in tobacco. Pp BBX 16 's overexpression in pear calli enhanced the red coloration during light treatments. Additionally, Pp BBX 16 's transient overexpression in pear peel increased anthocyanin accumulation, while virus‐induced gene silencing of Pp BBX 16 decreased anthocyanin accumulation. The expression patterns of pear BBX family members were analysed, and six additional BBX genes, which were differentially expressed during light‐induced anthocyanin biosynthesis, were identified. Thus, Pp BBX 16 is a positive regulator of light‐induced anthocyanin accumulation, but it could not directly induce the expression of the anthocyanin biosynthesis‐related genes by itself but needed Pp HY 5 to gain full function. Our work uncovered regulatory modes for Pp BBX 16 and suggested the potential functions of other pear BBX genes in the regulation of anthocyanin accumulation, thereby providing target genes for further studies on anthocyanin biosynthesis.