Screening of UV-B-induced genes from apple peels by SSH: possible involvement of MdCOP1-mediated signaling cascade genes in anthocyanin accumulation

Abstract

Suppression subtractive hybridization (SSH) was employed to identify candidate genes involved in red coloration in apple peel with the ultraviolet (UV)-B-treated 'Mutsu'. After reverse Northern blotting verification, nearly 80 clones were successfully sequenced. Large portions of the expressed sequence tags (ESTs) are well characterized anthocyanin biosynthesis-related genes, such as chalcone synthase (11A5), flavonol synthase (12F3), anthocyanidin synthase (11H5) and UDP-glycosyl transferase (14A12) whose presence proved the success of SSH. Eight ESTs were selected for quantitative real-time polymerase chain reaction analysis and their expressions were all elevated in 'Induction', further confirming the reliability of the SSH library. One EST, 11F4 (CONSTITUTIVE PHOTOMORPHOGENIC 1: COP1) with putative function in light signal relay was further analyzed in 'Mutsu' and 'Tsugaru', along with MdHY5 (ELONGATED HYPOCOTYL 5: the downstream target of COP1), MdMYB22 (a possible flavonol-specific activator under the regulation of HY5, belonging to the SG7/PRODUCTION OF FLAVONOL GLYCOSIDES family) and MdMYBA. Results showed that MdCOP1, MdHY5, MdMYB22 and MdMYBA were all UV-B inducible genes and anthocyanin accumulation occurred after their increased expressions. Moreover, their expressions and anthocyanin content were enhanced under UV-B plus 17°C treatment. The presence of G box, a known consensus binding site of HY5, in the MdMYBA promoter region implicated that it could be regulated by MdHY5, which was verified by the result of the yeast one-hybrid analysis. Our data suggested that UV-B irradiation would induce the utmost upstream light signaling factor, MdCOP1, which activates MdHY5 signaling by binding to the promoter regions of MdMYBs, and finally leads to the red coloration of apple peels.

Solar UV light regulates flavonoid metabolism in apple (Malus x domestica)

“…A study by Peng et al () has provided evidence for the same mechanism of UV‐B signalling in apple. Peng et al () suggested that UV‐B light induces COP1, which in turn activates HY5 binding to the promoter regions of other MYBs and finally leads to the accumulation of anthocyanins in apple peel.…”

“…A study by Peng et al () has provided evidence for the same mechanism of UV‐B signalling in apple. Peng et al () suggested that UV‐B light induces COP1, which in turn activates HY5 binding to the promoter regions of other MYBs and finally leads to the accumulation of anthocyanins in apple peel. It has also been shown that in Arabidopsis , HY5 can directly bind to the biosynthetic genes, such as CHS (Ang et al, ) and F3H (Lee et al, ).…”

“…This study shows that expression patterns of MYB22 correlate with FLS expression during apple fruit development and suggests that MYB22 activates the flavonol pathway by combining directly with the FLS promoter. With key players in the genetic control of flavonol and anthocyanin synthesis found, the impact of light exposure on apple flavonoid biosynthesis has begun to receive more attention (Feng, Li, Ma, & Cheng, ; Peng et al, ; Vimolmangkang et al, ; Wang et al, ), yet there is a lack of understanding regarding the role of UV light as a key driver of flavonoid regulation in apple.…”

“…Fruit displaying increased gene expression of MYB10, and all seven structural genes also showed raised levels of anthocyanins, flavonols, and total phenolics (Feng et al, ). Peng et al () showed that in UV‐B‐exposed apple peel, COP1, HY5, MYB22 (a flavonol‐specific activator), and MYB10 (an activator of anthocyanin biosynthesis) were all induced and anthocyanin accumulation increased following enhanced expression of these genes. The authors suggested that UV‐B light would alter the activity of the UVR8 and COP1 proteins, which in turn leads to HY5 inducing the transcription of MYB TFs.…”

Plant Hormones under Challenging Environmental Factors

“…The purpose is to inhibit chlorosis and bleaching on exposure to light, which can only be done if these genes are particularly upregulated. Peng et al ( 2013 ) reported the expression of MdMYBA and the related anthocyanin pathway genes in apple skin in response to UV-B stress. Agati et al ( 2013 ) reported the signifi cance of fl avonoids in their ability to scavenge ROS and control the development of individual organs and the whole plant.…”