The anthocyanin content in apple skin determines its red coloration, as seen in a Fuji apple mutant. Comparative RNA-seq analysis was performed to determine differentially expressed genes at different fruit development stages between the wild-type and the skin color mutant. A novel R2R3-MYB transcription factor, MdMYB90-like, was uncovered as the key regulatory gene for enhanced coloration in the mutant. The expression of MdMYB90-like was 21.3 times higher in the mutant. MdMYB90-like regulates anthocyanin biosynthesis directly through the activation of anthocyanin biosynthesis genes and indirectly through the activation of other transcription factors that activate anthocyanin biosynthesis. MdMYB90-like bound to the promoters of both structural genes (MdCHS and MdUFGT) and other transcription factor genes (MdMYB1 and MdbHLH3) in the yeast one-hybrid system, electrophoretic mobility shift assay, and dual-luciferase assay. Transgenic analysis showed that MdMYB90-like was localized in the nucleus, and its overexpression induced the expression of other anthocyanin-related genes, including MdCHS, MdCHI, MdANS, MdUFGT, MdbHLH3, and MdMYB1. The mutant had reduced levels of DNA methylation in two regions (−1183 to −988 and −2018 to −1778) of the MdMYB90-like gene promoter, which might explain the enhanced expression of the gene and the increased anthocyanin content in the mutant apple skin.

中文翻译：

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R2R3 型 MYB 转录因子 MdMYB90 样是苹果芽运动突变体皮肤颜色增强的原因

苹果皮中的花青素含量决定了它的红色，如富士苹果突变体中所见。进行比较 RNA-seq 分析以确定野生型和肤色突变体之间不同果实发育阶段的差异表达基因。一种新的 R2R3-MYB 转录因子，MdMYB90 样，被发现是增强突变体着色的关键调控基因。MdMYB90-like在突变体中的表达高出21.3倍。MdMYB90样通过激活花青素生物合成基因直接调节花青素生物合成，并通过激活其他激活花青素生物合成的转录因子间接调节花青素生物合成。MdMYB90样与两个结构基因的启动子结合（MdCHS和MdUFGT) 和其他转录因子基因 (MdMYB1和MdbHLH3) 在酵母单杂交系统、电泳迁移率变动分析和双荧光素酶分析中。转基因分析表明，MdMYB90-like 定位于细胞核，其过表达诱导了其他花青素相关基因的表达，包括MdCHS,MdCHI,MdANS,MdUFGT,MdbHLH3， 和MdMYB1. 该突变体的两个区域（-1183 至 -988 和 -2018 至 -1778）的 DNA 甲基化水平降低。MdMYB90样基因启动子，这可能解释了突变苹果皮中基因表达增强和花青素含量增加的原因。