Insights Into the Function of the NuA4 Complex in Plants.

Loreto Espinosa-Cores,Laura Bouza-Morcillo,Raquel Piqueras,Javier Barrero-Gil,Ana Lázaro,José A Jarillo,Manuel Piñeiro,Verónica Jiménez-Suárez

doi:10.3389/fpls.2020.00125

Abstract

Chromatin remodeling plays a key role in the establishment and maintenance of gene expression patterns essential for plant development and responses to environmental factors. Post-translational modification of histones, including acetylation, is one of the most relevant chromatin remodeling mechanisms that operate in eukaryotic cells. Histone acetylation is an evolutionarily conserved chromatin signature commonly associated with transcriptional activation. Histone acetylation levels are tightly regulated through the antagonistic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs). In plants, different families of HATs are present, including the MYST family, which comprises homologs of the catalytic subunit of the Nucleosome Acetyltransferase of H4 (NuA4) complex in yeast. This complex mediates acetylation of histones H4, H2A, and H2A.Z, and is involved in transcriptional regulation, heterochromatin silencing, cell cycle progression, and DNA repair in yeast. In Arabidopsis and, other plant species, homologs for most of the yeast NuA4 subunits are present and although the existence of this complex has not been demonstrated yet, compelling evidence supports the notion that this type of HAT complex functions from mosses to angiosperms. Recent proteomic studies show that several Arabidopsis homologs of NuA4 components, including the assembly platform proteins and the catalytic subunit, are associated in vivo with additional members of this complex suggesting that a NuA4-like HAT complex is present in plants. Furthermore, the functional characterization of some Arabidopsis NuA4 subunits has uncovered the involvement of these proteins in the regulation of different plant biological processes. Interestingly, for most of the mutant plants deficient in subunits of this complex characterized so far, conspicuous defects in flowering time are observed, suggesting a role for NuA4 in the control of this plant developmental program. Moreover, the participation of Arabidopsis NuA4 homologs in other developmental processes, such as gametophyte development, as well as in cell proliferation and stress and hormone responses, has also been reported. In this review, we summarize the current state of knowledge on plant putative NuA4 subunits and discuss the latest progress concerning the function of this chromatin modifying complex.

Highlights

In eukaryotic organisms, DNA is present in the nucleus in a highly compacted structure known as chromatin, in which nucleosomes are the basic structural units
Chromatin immunoprecipitation (ChIP) experiments demonstrated that FLC is a direct target of YAF9, and that the effect of this protein on FLC expression is mediated by changes in chromatin organization since the acetylation levels of both histone H4 and the histone variant H2A.Z were decreased in this locus in yaf9a and yaf9a yaf9b mutants (Figure 4A) (Zacharaki et al, 2012; Bieluszewski et al, 2015; Crevillén et al, 2019). These results reveal for the first time in plants a possible link between H2A.Z acetylation and gene expression that will have to be analyzed in detail in future works
The only information available to support the presence of Nucleosome Acetyltransferase of H4 (NuA4) in plants is based on proteomic and individual protein-protein interaction analyses performed in Arabidopsis

Summary

INTRODUCTION

DNA is present in the nucleus in a highly compacted structure known as chromatin, in which nucleosomes are the basic structural units. Most of the yeast NuA4 subunits are widely conserved in plants where more than one homolog for members of the complex are frequently found This is the case of Arabidopsis thaliana, in which many NuA4 components, including the putative catalytic subunits HISTONE ACETYLTRANSFERASE OF THE MYST FAMILY (HAM1/2) (Latrasse et al, 2008), are duplicated. Studies carried out in parallel performed cryoelectron microscopy and released the crystal structure of the Piccolo NuA4 core complex unveiling the histone H4 acetylation mechanism in the context of the nucleosome (Xu et al, 2016). This type of approach is shedding light on how this multisubunit complex assembles with the nucleosomal substrate to regulate gene expression

A Small Version of NuA4: the Piccolo NuA4 Complex

Findings

CONCLUDING REMARKS