A glutathione S-transferase GhTT19 determines flower petal pigmentation via regulating anthocyanin accumulation in cotton.

Anthocyanin accumulations in the flowers can improve seed production of hybrid lines, produce higher commodity value in cotton fiber. However, the genetic mechanism underlying the anthocyanin pigmentation in cotton petal is poorly understood. Here, we showed that the red petal phenotype was introgressed from Gossypium bickii through recombination with the segment containing R 3 bic region in A07 chromosome of G. hirsutum variety LR compared with the near-isogenic line of LW with white flower petals. The cyanidin-3-O-glucoside (Cy3G) was the major anthocyanin in red petals of cotton. A GhTT19 encoding a TT19-like GST was mapped to the R 3 bic site associated with red petal via map-based cloning, but GhTT19 homolog gene from D genome was not expressed in G. hirsutum. Intriguingly, allelic variations in the promoters between GhTT19 LW and GhTT19 LR , rather than genic regions, were found as genetic causal of petal color variations. GhTT19-GFP was found localized in both endoplasmic reticulum and tonoplast for facilitating anthocyanin transport. An additional MYB binding element found only in the promoter of GhTT19 LR , but not in that of GhTT19 LW , enhanced its transactivation by the MYB activator GhPAP1. Transgenic analysis confirmed the function of GhTT19 in regulating red flower phenotype in cotton. The essential light signaling component GhHY5 bond to and activated the promoter of GhPAP1, and GhHY5-GhPAP1 module together regulated GhTT19 expression to mediate the light-activation of petal anthocyanin pigmentation in cotton. This study provides new insights into the molecular mechanisms for anthocyanin accumulation and may lay a foundation for faster genetic improvement of cotton.