Insights Into the Function of the NuA4 Complex in Plants

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.

New Insights into Cellular Functions of Nuclear Actin

“…Either the complex is attached to the actin filament and moves along the filament propelled by the filament polymerization-depolymerization, or the monomeric actin directly interacts with the chromatin, or other unconventional forms of actin oligomers, performing some (currently unknown) functions in the chromatin remodeling complexes [ 16 ]. Another chromatin-modifying complex is the histone acetyltransferase complex NuA4/TIP60, which is involved in chromatin-binding, histone modifications, transcription, DNA damage response, control of the cell cycle, nonhomologous end joying, and homologous recombination [ 16 , 111 , 112 , 113 ]. Recent studies showed that the SWR1 remodeling complex deposits Htz1 histone into the chromatin and prevents genome instability, which is often associated with tumorigenesis [ 114 , 115 ].…”

CaSWC4 regulates the immunity-thermotolerance tradeoff by recruiting CabZIP63/CaWRKY40 to target genes and activating chromatin in pepper

“…The covalent histone modifications methylation and acetylation are regulated by the antagonistic activity of methyltransferases and demethylases [ 32 – 34 ] and of acetyltransferases/deacetylases [ 35 – 37 ], which emerge as complexes such as SET complexes (SET-C) [ 38 ] and histone acetyltransferases complexes (HAT-C). NuA3 [ 39 – 41 ] and NuA4 [ 42 ] are two classes of HAT-C that function in the acetylation of the histone H3 [ 43 ] and of the histones H4, H2A, and H2A.Z, respectively [ 44 , 45 ]. Each of these complexes comprises multiple members that associate with each other directly or indirectly, and each exhibits different and non-redundant functions [ 46 ], indicating that chromatin remodeling and histone modification are complex processes involving the coordinated action of multiple regulatory elements [ 43 ].…”

“…In addition, these complexes share common subunits. For example, ARP4, SWC4, YAF9, and RUVBL2 have been found in both NuA4-C and SWR1-C [ 42 , 44 , 47 , 48 ]. The significance of this sharing of components among different complexes is still not clear.…”

NuA4 and H2A.Z control environmental responses and autotrophic growth in Arabidopsis

“…Previous studies on Arabidopsis homologs of NuA4 subunits by affinity purification followed by mass spectrometry (AP-MS/MS) suggested that plant NuA4 resembles its yeast counterpart [15][16][17][18] . Importantly, the scaffold subunits Esa1-Associated Factor 1A/B (AtEAF1A/B), Transcription-Associated Protein 1 (AtTRA1) and Enhancer of Polycomb-Like 1A/B (AtEPL1A/B) were shown to be physically associated with the catalytic subunit homologs Histone Acetyltransferase of the MYST family 1/2 (HAM1/2) [16][17][18][19] .…”

“…Notably, AtTRA1 was also copurified with components of complexes responsible for H2A-H2A.Z exchange, suggesting a link between NuA4dependent histone acetylation and H2A.Z deposition 20,21 . AtEPL1 and AtEAF1 seem to be specific for NuA4, as they were not copurified with other chromatin complexes; thus, they are key to understanding NuA4 function 15,22,23 . In genetic studies, plant homologs of NuA4 subunits have been linked to gametogenesis, ABA responses, flowering time regulation, chlorophyll synthesis, cell growth, and ploidy 17,[24][25][26] .…”