Integrated metabolites and transcripts profiling reveal biosynthetic basis and regulation of color formation in pepper (Capsicum annuum L.) leaf

Pepper (Capsicum annuum L.) is a multi-year or annual vegetable crop of Solanaceae Capsicum genus. The previous research on pepper mainly focuses on pepper fruit and abiotic or biological stress of pepper. However, there are relatively few studies on the biological basis and regulatory mechanisms of the color changes in pepper leaves. This study revealed the mechanism of color changes in chili pepper leaves, providing new insights for further research on related metabolic pathways. A combined metabolome and transcriptome analyses of four different color pepper leaves was undertaken to study the color formation mechanism in pepper. A total of eighty flavonoids were identified in pepper leaves, flavones and flavonols were found significantly higher in white leaves, whereas anthocyanins were found most enriched in purple leaves. Through heat map, K-means, and KEGG enrichment analysis, the gene expression and regulatory patterns in the flavonoid biosynthesis pathway, chlorophyll biosynthesis and degradation pathway were analyzed. Based on the co-expression network diagram, transcription factor families such as MYB and bHLH that may be involved in regulating the formation of white and purple in pepper leaves were preliminarily screened. Transient overexpression experiments in tobacco indicated that capan00g003240 (CaMYB82) might regulate the biosynthetic pathway of flavonoids in pepper leaves by modulating the expression of structural genes. This result provides new insights for the regulation of pigments biosynthesis in pepper leaves.