Beyond HY5: COP1 Posttranslational Control of Anthocyanin Biosynthesis Proteins in Horticultural Crops

Anthocyanins are widespread specialized metabolites that provide pigmentation and antioxidant capacity, contributing to pollinator and seed-disperser attraction and to plant resistance to diverse environmental stresses. In human diets, anthocyanins are valued for their antioxidant and health-promoting properties. The biosynthetic pathway of anthocyanins is relatively conserved across plant species and is controlled by structural genes that encode the enzymes of the pathway along with regulatory genes, particularly transcription factors. This network integrates developmental and environmental signals, with light serving as a dominant cue: anthocyanins typically accumulate in light-exposed tissues and are repressed in darkness. A key node in this light-dependent switch is CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), an E3 ubiquitin ligase that, in the dark, promotes polyubiquitination and proteasome-mediated turnover of positive regulators of anthocyanin production. Although ELONGATED HYPOCOTYL 5 (HY5) is a canonical COP1 target and major activator of anthocyanin biosynthesis, COP1 control of this pathway extends well beyond HY5. Evidence from Arabidopsis and multiple horticultural crops, including apple, pear, eggplant, and tomato, indicates that COP1 also regulates anthocyanin accumulation through interactions with additional transcription factors and regulatory modules. Here, we synthesize recent advances in COP1-centered regulation of anthocyanin biosynthesis, with an emphasis on post-translational mechanisms and COP1 targets beyond HY5. We also discuss emerging opportunities to leverage this regulatory axis for nutritional improvement in horticultural species.