DNA methylation controlling abscisic acid catabolism responds to light to mediate strawberry fruit ripening

Abstract

Phytohormones, epigenetic regulation and environmental factors regulate fruit ripening but their interplay during strawberry fruit ripening remains to be determined. In this study, bagged strawberry fruit exhibited delayed ripening compared with fruit grown in normal light, correlating with reduced abscisic acid (ABA) accumulation. Transcription of the key ABA catabolism gene, ABA 8′-hydroxylase FaCYP707A4, was induced in bagged fruit. With light exclusion whole genome DNA methylation levels were up-regulated, corresponding to a delayed ripening process, while DNA methylation levels in the promoter of FaCYP707A4 were suppressed, correlating with increases in transcript and decreased ABA content. Experiments indicated FaCRY1, a blue light receptor repressed in bagged fruit and FaAGO4, a key protein involved in RNA-directed DNA methylation, could bind to the promoter of FaCYP707A4. The interaction between FaCRY1 and FaAGO4, and an increased enrichment of FaAGO4 directed to the FaCYP707A4 promoter in fruit grown under light suggests FaCRY1 may influence FaAGO4 to modulate the DNA methylation status of the FaCYP707A4 promoter. Furthermore, transient overexpression of FaCRY1, or an increase in FaCRY1 transcription by blue light treatment, increases the methylation level of the FaCYP707A4 promoter, while transient RNA interference of FaCRY1 displayed opposite phenotypes. These findings reveal a mechanism by which DNA methylation influences ABA catabolism, and participates in light-mediated strawberry ripening.