Leibniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany.
Plant Physiol. 2022 Nov 28;190(4):2417-2429. doi: 10.1093/plphys/kiac409.
Histone modifications are essential for chromatin activity and play an important role in many biological processes. Trimethylation of histone H3K27 (H3K27me3) is a repressive modification established by Polycomb Repressive Complex 2 (PRC2). Although the presence of the histone H3 serine 28 phosphorylation (H3S28ph) modification at adjacent amino acid residues has both positive and negative effects on Polycomb silencing in mammals, little is known about the effect of H3S28ph on H3K27me3-mediated gene silencing in plants. In this study, we show that mutating H3S28A in Arabidopsis (Arabidopsis thaliana) causes a dominant-negative effect that leads to an early-flowering phenotype by promoting the expression of flowering-promoting genes independently of abnormal cell division. While H3S28ph levels decreased due to the H3S28A mutation, H3K27me3 levels at the same loci did not increase. Moreover, we observed decreased H3K27me3 levels at some known PRC2 target genes in H3.3S28A transgenic lines, rather than the expected enhanced H3K27me3-mediated silencing. In line with the reduced H3K27me3 levels, the expression of the PRC2 catalytic subunits CURLY LEAF and SWINGER decreased. Taken together, these data demonstrate that H3.3S28 is required for PRC2-dependent H3K27me3-mediated silencing in Arabidopsis, suggesting that H3S28 has a noncanonical function in H3K27me3-mediated gene silencing.
组蛋白修饰对于染色质活性至关重要，在许多生物过程中发挥着重要作用。组蛋白 H3K27 的三甲基化（H3K27me3）是由多梳抑制复合物 2（PRC2）建立的一种抑制性修饰。尽管组蛋白 H3 丝氨酸 28 磷酸化（H3S28ph）修饰在相邻氨基酸残基上的存在对哺乳动物中的多梳沉默既有正面影响，也有负面影响，但对于 H3S28ph 对植物中 H3K27me3 介导的基因沉默的影响知之甚少。在本研究中，我们表明，拟南芥（Arabidopsis thaliana）中 H3S28A 的突变会导致显性负效应，通过独立于异常细胞分裂促进开花促进基因的表达而导致早花表型。虽然由于 H3S28A 突变导致 H3S28ph 水平降低，但同一基因座的 H3K27me3 水平并未增加。此外，我们观察到 H3.3S28A 转基因系中一些已知的 PRC2 靶基因的 H3K27me3 水平降低，而不是预期的增强 H3K27me3 介导的沉默。与降低的 H3K27me3 水平一致，PRC2 催化亚基 CURLY LEAF 和 SWINGER 的表达下降。综上所述，这些数据表明 H3.3S28 是拟南芥中 PRC2 依赖性 H3K27me3 介导的沉默所必需的，这表明 H3S28 在 H3K27me3 介导的基因沉默中具有非典型功能。
