Genome-wide identification and analysis of GH1-containing H1 histones among poplar species

Histone H1s are basic nuclear proteins, which played key role in the binding of DNA and nucleosome, eventually the stability of eukaryotic chromatin. In most species, H1s possess an evolutionarily conserved nucleosome-DNA binding globular domain (GH1), which is conserved between species, especially in mammals. However, there is limited information on the phylogeny, structure and function of H1s in poplar. In the present research, 21 GH1-containing proteins found in Populus trichocarpa were classified into three subgroups (H1s, Myb (SANK) GH1 and AT-hook GH1) based on their domains. The Populus H1 proteins contained lysine-rich N-, C-terminal tails and a conserved GH1 domain, particularly the characteristic amino acids in the helix and strand structures of the five H1 subtypes. The phylogenetic and structure diversity analysis of GH1 proteins across different Populus species and model plants revealed three conserved subgroups with characteristic amino acids. The variation in the number of members across the five subtypes was consistent with the evolutionary relationships among Populus species. The conserved characteristic amino acids among same Populus subtype can be served as markers for subtype identification. Furthermore, the abundance analysis of H1s in Populus indicated their unique functions in young tissues and stages, which may be related to DNA methylation. The consistent expression pattern of H1 across Populus species was in accordance with collinearity pairs. Present analyses provided valuable information on the diversity and evolution of H1s in Populus, advocating further research of H1s in plants.