Replacement of Arabidopsis H2A.Z with human H2A.Z orthologs reveals extensive functional conservation and limited importance of the N-terminal tail sequence for Arabidopsis development

The incorporation of histone variants, distinct paralogs of core histones, into chromatin affects all DNA-templated processes in the cell, including the regulation of transcription. In recent years, much research has been focused on H2A.Z, an evolutionarily conserved H2A variant found in all eukaryotes. In order to investigate the functional conservation of H2A.Z histones during eukaryotic evolution we transformed h2a.z deficient plants with three human H2A.Z proteins to assess their ability to rescue the mutant defects. We discovered that human H2A.Z.1 and H2A.Z.2.1 fully complement the phenotypic abnormalities of h2a.z plants despite the fact that Arabidopsis and human H2A.Z N-terminal tail sequences are quite divergent. In contrast, the brain-specific splice variant H2A.Z.2.2 has a dominant-negative effect in wild-type plants. Furthermore, H2A.Z.1 almost completely re-establishes normal H2A.Z chromatin occupancy in h2a.z plants and restores the transcript levels of more than 84 % of misexpressed genes. Finally, our hypothesis that the N-terminal tail of Arabidopsis H2A.Z is not crucial for its developmental functions was supported by the ability of N-terminal end truncations of Arabidopsis HTA11 to largely rescue the defects of h2a.z mutants.