Integrated metabolome and transcriptome analyses reveal the role played by CaWRKY44 during anthocyanins accumulation in pepper fruits

Pepper is an important vegetable and widely cultivated across the world. Anthocyanins play a crucial role in determining the color and nutritional value of pepper. In this study, light effects on anthocyanins accumulation in purple peppers were analyzed via bagging and non-bagging treatments. Transcription factor CaWRKY44 was identified as playing a key role in anthocyanins synthesis according to the metabolome and transcriptome analysis. CaWRKY44 expression increased during the different pepper pericarp developmental stages and a promoter cis-element analysis identified light and hormone-responsive elements and protein-binding motifs. VIGS-mediated silencing of CaWRKY44 reduced anthocyanins accumulation, while transient overexpression enhanced pigment deposition. Furthermore, the silencing or overexpression of CaWRKY44 modulated the expression level of anthocyanins biosynthetic structural genes. Our results indicated that CaWRKY44 could directly bind to the W-box cis-element in the CaDFR promoter and activates its transcription, which subsequently drives anthocyanins biosynthesis. The results could lay the foundation of the regulatory mechanism controlling anthocyanins biosynthesis in pepper.