Overexpression of HAT1 impairs histone H3 acetylation under high light conditions and a working model for HAT1 in repressing anthocyanin accumulation.

(A-C) ChIP-qPCR determines the histone H3 acetylation levels in the transcription start sites (TSSs) of DFR, LDOX, and UF3GT in Col-0, 35S:HAT1 #13, and hat1 under different conditions. The histone H3 acetylation levels were standardized to ACTIN 7 and results in the Col-0 under control conditions were set at 1. Error bars denote ± SD (n = 3). Different letters represented statistically significant differences (two-way ANOVA, pDFR, LDOX, and UF3GT in 35S:MYB75-HAT1N #2, 35S:HAT1 #13 35S:MYB75, and 35S:MYB75 under different conditions. The histone H3 acetylation levels were standardized to ACTIN 7 and results in the 35S:HAT1 #13 35S:MYB75 under control conditions were set at 1. Error bars denote ± SD (n = 3). Different letters represented statistically significant differences (two-way ANOVA, p<0.05). (G) Under non-inductive conditions, such as low light conditions, plants possess high levels of HAT1. Meanwhile, HAT1 interferes with MBW protein complex by binding MYB75 (Left), as well as transforming the active MBW protein complex into a repressive complex by recruiting EAR motif-dependent TPL corepressor (Right), thus preventing the expression of LBGs. (H) Under inductive conditions, such as high light conditions, HAT1 expression is suppressed. MYB75 and bHLH transcription factors are able to form MBW protein complex with TTG1 protein, and finally activates late biosynthetic genes expression.