CrWRKY42 positively regulates chlorophyll degradation and carotenoid biosynthesis in citrus

Abstract

AbstractChlorophyll degradation and carotenoid biosynthesis, which occur almost simultaneously during fruit ripening, are essential for coloration and nutritional value of fruits. However, the synergistic regulation of these two processes at transcriptional level remains largely unknown. Here, we identified a novel WRKY transcription factor CrWRKY42 from the transcriptome data of the yellowish bud mutant ‘Jinlegan’ tangor (MT) and its wild type ‘Shiranuhi’ tangor (WT), which was involved in the transcriptional regulation of both chlorophyll degradation and carotenoid biosynthesis pathways. CrWRKY42 activated the expression ofβ-carotene hydroxylase 1(CrBCH1) by directly binding to its promoter. Overexpression and interference ofCrWRKY42in citrus calli demonstrated thatCrWRKY42promoted carotenoid accumulation by inducing the expression of multiple carotenoid biosynthetic genes. Further assays confirmed that CrWRKY42 also directly bound to and activated the promoters of the genes involved in the carotenoid biosynthesis, includingphytoene desaturase(CrPDS) andlycopene β-cyclase 2(CrLCYB2). In addition, CrWRKY42 could also bind to the promoter ofSTAY-GREEN(CrSGR) and activated its expression, thus promoting chlorophyll degradation. Overexpression and silencing ofCrWRKY42in citrus fruits indicated that CrWRKY42 positively regulated chlorophyll degradation and carotenoid biosynthesis by synergistically activating the expressions of genes involved in both pathways. In conclusion, our data revealed that CrWRKY42 acted as a positive regulator of chlorophyll degradation and carotenoid biosynthesis to alter the conversion of citrus fruit color. Our findings provide insight into the complex transcriptional regulation of chlorophyll and carotenoid metabolism during fruit ripening.One Sentence SummaryThe CrWRKY42 transcription factor coordinates chlorophyll degradation and carotenoid biosynthesis by directly regulating genes involved in these pathways to alter the conversion of citrus fruit color.