Transcriptome and Metabolome-based Analysis of Anthocyanidin Biosynthesis in Purple Pepper

Abstract In order to clarify the profile of gene expression and metabolites for color formation and the molecular mechanism of anthocyanidin accumulation in purple pepper fruits, we analyzed the anthocyanidin metabolome data of the fruits of 2 purple pepper lines and 1 green pepper line and detected a total of 5 anthocyanidin-like metabolites, of which delphin chloride was unique to purple pepper fruits and 3 other anthocyanidin-like substances shared the metabolic pathway ko00942 and were up-regulated. Based on the transcriptome data, three pathways (ko00360, ko00400, and ko00941) related to anthocyanidin metabolism were identified through KEGG analysis. Three enzymes (DFR, ANS, and UFGT) and three transcription factors (MYB, BHLH, and WD40) in the purple pepper anthocyanidin biosynthetic pathway were up-regulated. We proposed a model to explain the regulation of pepper anthocyanidin biosynthesis: MYB, BHLH, and WD40 formed a ternary complex and bound to the specific cis-acting elements in the promoter region of the structural genes related to anthocyanidin biosynthesis to directly regulate their transcription, which resulted in the accumulation of a large amount of anthocyanidin metabolites including delphinidin 3-O-glucoside, delphinidin 3-O-rutinoside, and delphin chloride, giving color to pepper fruits. This study clarified the metabolic pathways and key genes affecting the color of purple pepper fruits and provided new insights into the synthesis and accumulation of anthocyanidins in pepper fruits.