JIPB|山东大学向凤宁实验室揭示FWA 启动子的胞嘧啶甲基化促进拟南芥直接离体不定芽再生

启动子序列中的表观遗传修饰可以作为基因表达的调节因子。不定芽再生同时受到 DNA 甲基化和组蛋白甲基化的影响，但是这种调节的机制基础是模糊的。在这里，我们鉴定了218个与愈伤组织再生能力相关的基因，这些基因在拟南芥中差异转录于可再生愈伤组织(RC)和非可再生愈伤组织(NRC)。通过对5个差异表达基因(FWA、 ACC1、 TFL1、 MAX3和 GRP3)启动子的分析，发现胞嘧啶甲基化与转录呈负相关。FWA 启动子在 NRC 中被去甲基化和高表达，而在 RC 中被甲基化和低表达。低甲基化突变体 FWA-1和 FWA-2的外植体表达水平较高，再生能力低于野生型，说明 FWA 抑制了离体芽的直接再生。WUSCHEL-RELATED HOMEOBOX 9(WOX9)是茎尖分生组织形成所必需的基因，FWA 直接抑制该基因的表达。过量表达 WOX9部分解决了 fwa-2植株的不定芽再生缺陷。这些发现提示 FWA 启动子的胞嘧啶甲基化是调控愈伤组织再生和直接离体芽再生的调控系统的一部分。

Epigenetic modifications within promoter sequences can act as regulators of gene expression. Shoot regeneration is influenced by both DNA methylation and histone methylation, but the mechanistic basis of this regulation is obscure. Here, we identified 218 genes related to the regeneration capacity of callus that were differentially transcribed between regenerable calli (RC) and non-regenerable calli (NRC) in Arabidopsis thaliana. An analysis of the promoters of five of the differentially expressed genes (FWA, ACC1, TFL1, MAX3, and GRP3) pointed to an inverse relationship between cytosine methylation and transcription. The FWA promoter was demethylated and highly expressed in NRC, whereas it was methylated and expressed at low levels in RC. Explants of the hypomethylation mutants fwa-1 and fwa-2 showed strong levels of FWA expression and regenerated less readily than the wild type, suggesting that FWA inhibits direct in vitro shoot regeneration. WUSCHEL-RELATED HOMEOBOX 9 (WOX9), which is required for shoot apical meristem formation, was directly repressed by FWA. Overexpressing WOX9 partly rescued the shoot regeneration defect of fwa-2 plants. These findings suggest that cytosine methylation of the FWA promoter forms part of the regulatory system governing callus regenerability and direct in vitro shoot regeneration.

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