Integrated metabolome and transcriptome analysis provides clues to fruit color formation of yellow, orange, and red bell pepper

Fruit color is a crucial trait for bell pepper. To investigate the mechanism of color formation, three bell pepper lines with different color (yellow, orange and red) were used as materials to conduct comprehensive targeted metabolomic and transcriptomic analyses. During the process of fruit development, 54 carotenoids metabolites were discovered, exhibiting unique accumulation patterns and notable variety specificity. The types and content of carotenoids in orange fruit (OM) were notably greater compared to the other two varieties. Red pigment (capsanthin and capsorubin) was specifically enriched in red fruit (RM), and yellow pigment (lutein and zeaxanthin) is the highest in yellow fruit (YM) and OM. Five modules positively correlated with carotenoid accumulation and one negative module was determined by weighted gene co-expression network analysis (WGCNA). Additionally, transcription factors (TFs) and hub genes related to carotenoid synthesis were predicted. By elucidating the regulation of 7 key carotenoid metabolites by 14 critical genes, we constructed a comprehensive carotenoid biosynthesis metabolic network that comprehensively explains the pigment changes observed in green and mature pepper fruit. Overall, the results not only provide important insights into carotenoid synthesis pathway, but also lay a solid base for revealing the mechanism of bell pepper color transformation.