Abstract
While the yeast Chz1 acts as a specific histone-chaperone for H2A.Z, functions of CHZ-domain proteins in multicellular eukaryotes remain obscure. Here, we report on the functional characterization of OsChz1, a sole CHZ-domain protein identified in rice. OsChz1 interacts with both the canonical H2A-H2B dimer and the variant H2A.Z-H2B dimer. Within crystal structure the C-terminal region of OsChz1 binds H2A-H2B via an acidic region, pointing to a previously unknown recognition mechanism. Knockout of OsChz1 leads to multiple plant developmental defects. At genome-wide level, loss of OsChz1 causes mis-regulations of thousands of genes and broad alterations of nucleosome occupancy as well as reductions of H2A.Z-enrichment. While OsChz1 associates with chromatin regions enriched of repressive histone marks (H3K27me3 and H3K4me2), its loss does not affect the genome landscape of DNA methylation. Taken together, it is emerging that OsChz1 functions as an important H2A/H2A.Z-H2B chaperone in dynamic regulation of chromatin for higher eukaryote development.
Highlights
While the yeast Chz[1] acts as a specific histone-chaperone for H2A.Z, functions of CHZdomain proteins in multicellular eukaryotes remain obscure
YChz[1] forms a long irregular chain capped by two short α-helix motifs when it binds to H2A.Z-H2B, and the binding of yChz[1] to H2A.Z-H2B enhances the stability of the yChz1-H2A.Z-H2B complex28,29. yChz[1] binds at a specific surface of H2A.Z, which differs from the yeast NAP1 (yNAP1)-binding surface, and yChz[1] and yNAP1 exhibit both redundant and distinct functions in the subcellular transport and the chromatin incorporation of H2A.Z30–32
CHZ-domain proteins are well-conserved during the green lineage evolution and are found in organisms ranging from unicellular algae to vasculature higher plants (Fig. 1a)
Summary
While the yeast Chz[1] acts as a specific histone-chaperone for H2A.Z, functions of CHZdomain proteins in multicellular eukaryotes remain obscure. While OsChz[1] associates with chromatin regions enriched of repressive histone marks (H3K27me[3] and H3K4me2), its loss does not affect the genome landscape of DNA methylation. It is emerging that OsChz[1] functions as an important H2A/H2A.Z-H2B chaperone in dynamic regulation of chromatin for higher eukaryote development. Nucleosome is the fundamental structural unit of chromatin in eukaryotes It is composed of almost two superhelical turns of DNA (∼146 bp) wrapped around an octamer formed by two copies each of the four core histone proteins H2A, H2B, H3, and H41. Either free or yNAP1-associated H2A.Z-H2B dimers could be transferred by the ATP-dependent chromatin-remodeling complex SWR1 (SWR1-c) to replace H2A-H2B in an in vitro nucleosome assembly assay, implying that yNAP1 functions as an escort rather than part of the histone transfer machinery[27]. Instead of working in H2A.Z incorporation, the Arabidopsis NAP1-RELATED PROTEIN1 (NRP1) and NRP2 were proposed to regulate gene expression by counteracting SWR1 to prevent excessive accumulation of H2A.Z in chromatin[34]
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