Evolution and conservation of JmjC domain proteins in the green lineage

Histone modification regulates plant development events by epigenetically silencing or activating gene expression, and histone methylation is regulated by histone lysine methyltransferases (KMTs) and histone lysine demethylases (KDMs). The JmjC domain proteins, an important KDM family, erase methyl marks (CH3-) from histones and play key roles in maintaining homeostasis of histone methylation in vivo. Here, we analyzed 169 JmjC domain proteins from whole genomes of plants ranging from green alga to higher plants together with 36 from two animals (fruit fly and human). The plant JmjC domain proteins were divided into seven groups. Group-I KDM4/JHDM3 and Group-V JMJD6 were found in all the plant species and the other groups were detected mainly in vascular or seed plants. Group-I KDM4/JHDM3 was potentially associated with demethylation of H3K9me2/3, H3K27me2/3, and H3K36me1/2/3, Group-II KDM5A with H3K4me1/2/3, Group-III KDM5B with H3K4me1/2/3 and H3K9me1/2/3, Group-V JMJD6 with H3R2, H4R3, and hydroxylation of H4, and Group-VII KDM3/JHDM2 with H3K9me1/2/3. Group-IV/Group-VI JmjC domain-only A/B proteins were involved in hydroxylation and demethylation of unknown substrate sites. The binding sites for the cofactors Fe(II) and alpha-ketoglutarate in the JmjC domains also were analyzed. In the alpha-ketoglutarate binding sites, Thr/Phe/Ser and Lys were conserved and in the Fe(II) binding sites, two His and Glu/Asp were conserved. The results show that JmjC domain proteins are a conserved family in which domain organization and cofactor binding sites have been modified in some species. Our results provide insights into KDM evolution and lay a foundation for functional characterization of KDMs.