The histone acetylation module and histone chaperone in the Arabidopsis NuB4 complex have synergistic effect on chromatin accessibility (ChIP-Seq)
Although the conserved type B histone acetyltransferase is known to regulate both cytoplasmic histone acetylation and nuclear nucleosome assembly, the coordination between the dual functions remains poorly understood. Our study revealed that the Arabidopsis thaliana type B histone acetyltransferase HAG2 interactions with the histone chaperones MSI2, MSI3, and NASP, as well as histones H3 and H4, resulting in the formation of a conserved NuB4 complex. Within this complex, HAG2, MSI2, and MSI3 constitute a histone acetylation module that acetylates newly synthesized histone H4 at lysine 5 and 12 sites in the cytoplasm. This module collaborates with NASP to maintain the abundance of H3 and H4 proteins in the cytoplasm, but it is not necessary for nucleosome assembly in the nucleus, which differs from the role of NuB4 complexes in other eukaryotes. Furthermore, we found that, within the nucleus, the collaborative actions of the histone acetylation module and NASP enhance chromatin accessibility near the transcription start sites of protein-coding genes, while showing a negative impact on chromatin accessibility near the transcription termination sites. This suggests that the Arabidopsis NuB4 complex is responsible for modulating chromatin accessibility across the entire genome, highlighting a plant-specific function of the NuB4 complex. Overall design: Examination of H4K12Ac levels in wild type and two mutants