Phylogeny-based systematization of Arabidopsis proteins with histone H1 globular domain

H1 (or linker) histones are basic nuclear proteins that possess an evolutionarily-conserved nucleosome-binding globular domain - GH1. They perform critical functions in determining the accessibility of chromatin DNA to trans-acting factors. In most metazoan species so far studied, linker histones are highly heterogeneous, with numerous non-allelic variants co-occurring in the same cells. The phylogenetic relationships among these variants as well as their structural and functional properties have been relatively well established. This contrasts markedly with the rather limited knowledge concerning the phylogeny and structural and functional roles of an unusually diverse group of GH1-containing proteins in plants. The dearth of information and lack of a coherent phylogeny-based nomenclature of these proteins can lead to misunderstandings as to their identity and possible relationships, thereby hampering plant chromatin research. Based on published data and our in silico and high-throughput analyses, we propose a systematization and coherent nomenclature of GH1-containing proteins of Arabidopsis that will be useful for both identification and structural and functional characterization of homologous proteins from other plant species.