FcMET1 mediates low DNA methylation and promotes peel coloring in Ficus carica

Abstract

Fig (Ficus carica L.) with purple-red peel cultivars are popular among consumers and exhibit better storability. While DNA methylation influences fruit ripening and color development, its specific role in fig fruit remains unclear. This study explores the impact of DNA methylation on the fig peel coloration. Enzymatic colorimetric detection revealed that the level of ‘Purple Peel’ fig DNA methylation decreases with fig fruit ripening and coloring. Treatment of young fruit with the DNA-methylation inhibitor azacytidine induced peel coloration, suggesting that a decrease in DNA-methylation level promotes fig peel coloration. Seven members of DNA methyltransferases and three members of DNA demethylases were identified from a high-level fig genome, highlighting FcMET1 and FcDRM2 as stable proteins, ensuring functional expression. Reference to the Arabidopsis protein interaction network map predicted that FcMET1 is in a central position, suggesting a crucial regulatory role in multiple biological processes. Correlation analysis revealed a positive correlation between FcMET1 expression during peel development and the level of total DNA methylation. Weighted gene co-expression network analysis identified co-expression of FcMET1 with the color-related transcription factors MYB, bHLH and WD40, as well as with eight structural genes in the flavonoid-biosynthesis pathway. The expression of FcUFGT3 was negatively correlated with that of FcMET1. McrBC-PCR and Bisulfite Sequencing detection showed that a low methylation level of the FcUFGT3 promoter corresponds with its high expression in colored fig. This investigation of the mechanism of DNA methylation provides a theoretical basis for understanding the role of DNA-methylation modifications in fig ripening and coloring.