The Genome-Wide Identification of the GST Gene Family and Functional Characterization of PsGSTF8 in Anthocyanin Accumulation in Chinese Plum Fruit (Prunus salicina)

Anthocyanins are major determinants of both the color and nutritional quality of fruit. Their accumulation in plant tissues depends on biosynthesis as well as efficient transport into the vacuole, a process in which glutathione S-transferases (GSTs) are believed to play an important role. Through genome-wide identification and analysis, this study identified 39 Chinese plum (Prunus salicina) glutathione S-transferase (PsGST) genes. Phylogenetic analysis grouped these PsGST genes into seven subfamilies. Dispersed duplication appeared to be the main driver of family expansion, and the duplicated genes appear to have largely evolved under purifying selection. The cultivar ‘Fengweimeigui’ (FWMG), with purple peel and red pulp, and the cultivar ‘Fengweihuanghou’ (FWHH), with yellow peel and yellow pulp, were used as contrasting materials because of their distinct anthocyanin pigmentation. We then profiled anthocyanin accumulation and the expression patterns of all PsGST genes across fruit development using quantitative real-time PCR (qRT-PCR). PsGSTF8 was identified as a candidate gene, and its expression patterns in both peel and pulp were consistent with anthocyanin accumulation, with higher relative transcript levels in the deeply colored cultivar ‘FWMG’ and undetectable expression in ‘FWHH’. The transient overexpression of PsGSTF8 in Chinese plum fruit promoted anthocyanin accumulation, and the complementation of the Arabidopsis thaliana transparent testa 19 (tt19) mutant further supported the potential role of PsGSTF8 in anthocyanin accumulation and GST-mediated transport. These results provide new clues for understanding potential GST-mediated anthocyanin transport and accumulation and offer a basis for the further investigation of the molecular mechanisms underlying fruit coloration in Chinese plum.