DNA methylation mediated by RdDM pathway and demethylation affects furanone accumulation through regulation of <i>QUINONE OXIDOREDUCTASE</i> in strawberry

Abstract

Recently, increasing evidence suggests that DNA methylation plays a crucial role in fruit ripening. However, the role of DNA methylation in regulating specific traits, such as flavor, remains unclear. Here, we report a role of DNA methylation in affecting furanone biosynthesis in strawberry. Strawberry quinone oxidoreductase (FaQR) is a key enzyme in furanone biosynthesis. There are four <i>FaQR</i> homologs in strawberry cultivar 'Yuexin', and one of them, <i>FaQR3</i>, contributes ~50% of <i>FaQR</i> transcripts, indicating a major role of <i>FaQR3</i> in furanone biosynthesis. Through characterization of levels of DNA methylation and <i>FaQR3</i> transcript and furanone contents during fruit ripening and after the application of DNA methylation inhibitor, we found that the DNA methylation level of the <i>FaQR3</i> promoter was negatively correlated with <i>FaQR3</i> expression and furanone accumulation, suggesting that DNA methylation may be involved in furanone biosynthesis through adjusting <i>FaQR3</i> expression, and responded to different temperatures consistently. In addition, transient expression of a gene in the RNA-directed DNA methylation (RdDM) pathway, <i>FaAGO4</i>, and enrichment analysis of the 24-nucleotide siRNAs suggested that DNA methylation in the <i>FaQR3</i> promoter is mediated by the RdDM pathway. Transient RNA interference (RNAi) of <i>FaDML</i> indicated that the demethylation pathway may be involved in regulating furanone accumulation. These findings provide new insights into the role of DNA methylation and demethylation in affecting flavor quality in strawberry during fruit ripening.