The Arabidopsis NuA4 histone acetyltransferase complex is required for chlorophyll biosynthesis and photosynthesis. [ChIP-Seq]

Although two Enhancer of Polycomb-like proteins, EPL1A and EPL1B (EPL1A/B), are known to be conserved and characteristic subunits of the NuA4-type histone acetyltransferase complex in Arabidopsis thaliana, the biological function of EPL1A/B and the mechanism by which EPL1A/B function in the complex remain unknown. Here, we report that EPL1A/B are required for the histone acetyltransferase activity of the NuA4 complex on the nucleosomal histone H4 in vitro and for the enrichment of histone H4K5 acetylation at thousands of protein-coding genes in vivo. We demonstrate that EPL1A/B are required for linking the NuA4 catalytic subunit HAM1 with accessory subunits in the NuA4 complex. EPL1A/B function redundantly in regulating plant development especially in chlorophyll biosynthesis and de-etiolation. The EPL1A/B-dependent transcription and H4K5Ac are enriched at genes involved in chlorophyll biosynthesis and photosynthesis. We also find that EAF6, another characteristic subunit of the NuA4 complex, contribute to de-etiolation. These results suggest that the Arabidopsis NuA4 complex components function as a whole to mediate histone acetylation and transcriptional activation specifically at light-responsive genes and are critical for photomorphogenesis. Examination of H4K5Ac levels in wild type and epl1a/b mutant.

尽管两类多梳样增强子蛋白（Enhancer of Polycomb-like proteins）EPL1A与EPL1B（下称EPL1A/B）已被证实为拟南芥（Arabidopsis thaliana）中NuA4型组蛋白乙酰转移酶复合物（NuA4-type histone acetyltransferase complex）的保守特征性亚基，但EPL1A/B的生物学功能及其在复合物中的作用机制仍未明确。本研究发现，EPL1A/B对于NuA4复合物在体外介导核小体组蛋白H4（nucleosomal histone H4）的乙酰转移酶活性，以及在体内于数千个蛋白编码基因上介导组蛋白H4K5乙酰化（histone H4K5 acetylation）富集均不可或缺。本研究证实，EPL1A/B是连接NuA4复合物催化亚基HAM1与辅助亚基的必要组分。EPL1A/B在调控植物发育，尤其是叶绿素生物合成与去黄化（de-etiolation）过程中功能冗余。依赖EPL1A/B的转录调控及H4K5乙酰化修饰（H4K5Ac）均富集于参与叶绿素生物合成与光合作用的基因中。本研究同时发现，NuA4复合物的另一特征亚基EAF6同样参与调控植物去黄化过程。上述结果表明，拟南芥NuA4复合物各组分协同发挥功能，特异性介导光响应基因的组蛋白乙酰化与转录激活，且对植物光形态建成（photomorphogenesis）至关重要。对野生型与epl1a/b突变体的H4K5乙酰化水平进行检测。