Methylation of <i>AcGST1</i> Is Associated with Anthocyanin Accumulation in the Kiwifruit Outer Pericarp

Abstract

Most red-fleshed kiwifruit cultivars, such as Hongyang, only accumulate anthocyanins in the inner pericarp; the trait of full red flesh becomes the goal pursued by breeders. In this study, we identified a mutant "H-16" showing a red color in both the inner and outer pericarps, and the underlying mechanism was explored. Through transcriptome analysis, a key differentially expressed gene <i>AcGST1</i> was screened out, which was positively correlated with anthocyanin accumulation in the outer pericarp. The result of McrBC-PCR and bisulfite sequencing revealed that the SG3 region (-292 to -597 bp) of <i>AcGST1</i> promoter in "H-16" had a significantly lower CHH cytosine methylation level than that in Hongyang, accompanied by low expression of methyltransferase genes (<i>MET1</i> and <i>CMT2</i>) and high expression of demethylase genes (<i>ROS1</i> and <i>DML1</i>). Transient calli transformation confirmed that demethylase gene <i>DML1</i> can activate transcription of <i>AcGST1</i> to enhance its expression. Overexpression of <i>AcGST1</i> enhanced the anthocyanin accumulation in the fruit flesh and leaves of the transgenic lines. These results suggested that a decrease in the methylation level of the <i>AcGST1</i> promoter may contribute to accumulation of anthocyanin in the outer pericarp of "H-16".