ArMYB89 and ArCOP1 interaction modulates anthocyanin biosynthesis in Acer rubrum leaves under low‐temperature conditions

Acer rubrum, a famous ornamental tree, produces bright red-coloured leaves because of the temperature decline from summer to autumn. This process's molecular mechanism is elusive, so we have investigated how anthocyanin biosynthesis is induced in A. rubrum leaves under low temperatures. The results of low-temperature treatment under light and dark conditions showed that the low-temperature promoted anthocyanin accumulation in A. rubrum is light-dependent. The transcriptome analysis showed that ArMYB89 was significantly highly expressed in leaves of A. rubrum growing under low temperatures with light conditions. The findings from the Dap-seq analysis, yeast one hybridisation, electrophoretic mobility shift assay and luciferase reporter assay indicated that the ArMYB89 transcription factor binds directly to the promoter of ArUGT52 and stimulates its transcription. The co-expression of ArUGT52 with ArMYB89 significantly induced anthocyanin levels under low temperatures with light conditions. Enzyme activity analysis showed that ArUGT52 could convert Cyanidins and Pelargonidins into Cyanidin-3-O-glucoside and Pelargonidin 3-glucoside, which are considered the main anthocyanins in red colour leaves of A. rubrum. The results of yeast two hybridisation, pulldown assay and bimolecular fluorescence complementation experiment showed an interaction between COP1 and ArMYB89, while in vivo and in vitro protein ubiquitination assay demonstrated that ArCOP1 ubiquitinates ArMYB89. Notably, co-expression of ArCOP1 with ArMYB89 significantly reduced anthocyanin levels, while the virus-induced gene silencing of ArCOP1 significantly induced anthocyanin levels under low temperatures with light conditions. In conclusion, this work revealed the molecular mechanism regulating anthocyanin accumulation in the A. rubrum leaves under low temperatures.