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

Abstract

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 BBX22, PpBBX16, was differentially expressed after fruits were removed from bags and may be involved in anthocyanin biosynthesis. Here, the expression and function of PpBBX16 were analysed. PpBBX16's expression was highly induced by white‐light irradiation, as was anthocyanin accumulation. PpBBX16's ectopic expression in Arabidopsis increased anthocyanin biosynthesis in the hypocotyls and tops of flower stalks. PpBBX16 was localized in the nucleus and showed trans‐activity in yeast cells. Although PpBBX16 could not directly bind to the promoter of PpMYB10 or PpCHS in yeast one‐hybrid assays, the complex of PpBBX16/PpHY5 strongly trans‐activated anthocyanin pathway genes in tobacco. PpBBX16's overexpression in pear calli enhanced the red coloration during light treatments. Additionally, PpBBX16's transient overexpression in pear peel increased anthocyanin accumulation, while virus‐induced gene silencing of PpBBX16 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, PpBBX16 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 PpHY5 to gain full function. Our work uncovered regulatory modes for PpBBX16 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.

ABA‐responsive ABRE‐BINDING FACTOR3 activates DAM3 expression to promote bud dormancy in Asian pear

“…Transgenic Arabidopsis plants were selected on half‐strength Murashige and Skoog (MS) medium supplemented with 20 mg/L hygromycin. The EHA105 cells harbouring the 35S:HA‐ABF3 or 35S:HA‐DAM3 construct were used to transform pear calli as previously described (Bai, Tao, Tang, et al, ). Control calli were transformed with the 35:HA‐GFP construct.…”

Retrotransposon promoter of Ruby1 controls both light‐ and cold‐induced accumulation of anthocyanins in blood orange

“…HY5 is a basic leucine zipper (bZIP) transcription factor involved in light‐induced anthocyanin biosynthesis by directly binding to the G‐box motif within the promoter of R2R3 MYB regulators of anthocyanin biosynthesis and promoting anthocyanin accumulation (An et al, ; M. Jiang et al, ; Qiu et al, ; Shin et al, ). In combination with HY5 protein, B‐box containing zinc‐finger proteins were shown to activate anthocyanin genes in Arabidopsis and red pear (Bai et al, ; D. Xu et al, ). The ubiquitin E3 ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) is responsible for the ubiquitination and degradation of MdMYB1 protein (Li et al, ) or PRODUCTION OF ANTHOCYANIN PIGMENT1 (PAP1) and PAP2 proteins (Maier et al, ) in the dark.…”

“…HY5 is a basic leucine zipper (bZIP) transcription factor involved in light-induced anthocyanin biosynthesis by directly binding to the G-box motif within the promoter of R2R3 MYB regulators of anthocyanin biosynthesis and promoting anthocyanin accumulation Qiu et al, 2018;Shin et al, 2013). In combination with HY5 protein, B-box containing zinc-finger proteins were shown to activate anthocyanin genes in Arabidopsis and red pear (Bai et al, 2019;D. Xu et al, 2016).…”

MdBBX22 regulates UV‐B‐induced anthocyanin biosynthesis through regulating the function of MdHY5 and is targeted by MdBT2 for 26S proteasome‐mediated degradation

“…BBX proteins play an array of diverse physiological functions in plant growth and development, and in both biotic and abiotic stress responses (Gangappa and Botto, 2014). Previous reports have shown that BBX proteins are involved in regulating anthocyanin biosynthesis in pear and apple (Bai et al, 2019;Fang et al, 2019). Here, we identified the role of MdBBX22 in UV-B-induced anthocyanin biosynthesis.…”

“…These results provide evidence that MdBBX22 promotes UV-B-induced anthocyanin biosynthesis by MdBBX22-MdHY5 interaction. Given that MdBBX22 has similar mechanisms to PpBBX16 (Bai et al, 2019) and MdBBX20 (Fang et al, 2019) in regulating anthocyanin biosynthesis, we suspect that they may play a redundant role in this process. In addition to MdBBX22, we also found that MdBBX24 and MdBBX33 interacted with MdHY5 ( Figure 1l), indicating that MdHY5 might act a central role in the regulation of anthocyanin biosynthesis and BBXs-HY5 interaction is a universal regulatory module Botto, 2014, 2016).…”