Metabolome and Transcriptome Analyses of the Molecular Mechanism Underlying Light-Induced Anthocyanin Accumulation in Pepper (Capsicum annuum L.) Peel.

Abstract

Under light exposure, certain pepper cultivars synthesize large amounts of anthocyanins in their pericarps, with the illuminated areas exhibiting black coloration. However, research on light-induced anthocyanin formation in pepper fruit, particularly the related metabolites and genetic changes, remains limited. To identify the key genes involved in localized anthocyanin synthesis under light conditions, we investigated the black pericarps (light-exposed) and green pericarps of pepper variety MSCJ1 under illumination. Metabolomics analysis identified 579 metabolites in the black and green pepper pericarps, with 50 differentially accumulated metabolites. Petunidin-3-(6″-p-coumaroyl-glucoside) and delphinidin-3-p-coumaroyl-rutinoid accumulation represented the main factor underlying light-induced blackening of the pericarp. RNA-seq identified 121 differentially expressed genes that were significantly enriched in the flavonoid biosynthesis pathway. The genes for phenylalanine ammonia lyase (Capana09g002200, Capna09g002190), cinnamic acid hydroxylase (Capana06g000273), chalcone synthase (Capana05g002274), flavonoid 3-hydroxylase (Capana02g002586), flavonoid 3'-hydroxylase (MSTRG.15987), dihydroflavonol 4-reductase (Capana02g002763), anthocyanin synthase (Capana01g000365), UDP glucosyltransferase (Capana03g000135), and glutathione S-transferase (Capana02g002285) were key genes for anthocyanin synthesis and transport. Transcription factors bHLH (Capana09g001426, Capana09g001427), HSFB3 (Capana05g000086), and TCP4 (Capana07g002142) participated in the regulation of anthocyanin synthesis. These results broaden our understanding of the mechanism of light-induced anthocyanin synthesis in pepper peel.