Background. Jumonji C ( JmjC ) proteins exert critical roles in plant development and stress response through the removal of lysine methylation from histones. Brassica napus, which originated from spontaneous hybridization by Brassica rapa and Brassica oleracea, is the most important oilseed crop after soybean. In JmjC proteins of Brassica species, the structure and function and its relationship with the parents and model plant Arabidopsis thaliana remain uncharacterized. Systematic

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... on and analysis for JmjC family in Brassica crops can facilitate the future functional characterization and oilseed crops improvement. Methods. Basing on the conserved JmjC domain, JmjC homologs from the three Brassica species, B. rapa (AA), B. oleracea (CC) and B. napus, were identified from the Brassica database. Some methods, such as phylogenic analysis , chromosomal mapping, HMMER searching, gene structure display and Logos analysis, were used to characterize relationships of the JmjC homologs. synonymous and nonsynonymous nucleotide substitutions were used to infer the information of gene duplication among homologs. Then, the expression level of BnKDM5 subfamily genes were checked under abiotic stress by qRT-PCR. Results. 65 JmjC genes were identified from B. napus genome, 29 from B. rapa, and 23 from B. oleracea. These genes were grouped into seven clades base on the phylogenetic analysis, and their catalytic activities of demethylation were predicted. The average retention rate of B. napus JmjC genes (B. napus JmjC gene from B. rapa (93.1%) and B. oleracea (82.6%)) exceeded whole genome level. JmjC sequences demonstrated high conservation in domain origination, chromosomal location, intron/exon number and catalytic sites. The gene duplication events were confirmed among the homologs. Furthermore, BrKDM5 subfamily genes were examined under stress conditions. A lot of BrKDM5 subfamily genes show higher expression under drought and NaCl treatment, but only a few genes are involved in high temperature stress. Conclusions. This study provides the first genome-wide characterization of JmjC genes in Brassica species. The BnJmjC exhibits higher conservation during the formation process of allotetraploid than the average retention rates of whole B. napus genome. Furthermore, expression profiles indicated that BnKDM5 subfamily genes are involved in stress response to salt, drought and high temperature. Abstract Background. Jumonji C (JmjC) proteins exert critical roles in plant development and stress response through the removal of lysine methylation from histones. Brassica napus, which originated from spontaneous hybridization by Brassica rapa and Brassica oleracea, is the most important oilseed crop after soybean. In JmjC proteins of Brassica species, the structure and function and its relationship with the parents and model plant Arabidopsis thaliana remain uncharacterized. Systematic identification and analysis for JmjC family in Brassica crops can facilitate the future functional characterization and oilseed crops improvement. Methods. Basing on the conserved JmjC domain, JmjC homologs from the three Brassica species, B. rapa (AA), B. oleracea (CC) and B. napus, were identified from the Brassica database. Some methods, such as phylogenic analysis, chromosomal mapping, HMMER searching, gene structure display and Logos analysis, were used to characterize relationships of the JmjC homologs. synonymous and nonsynonymous nucleotide substitutions were used to infer the information of gene duplication among homologs. Then, the expression level of BnKDM5 subfamily genes were checked under abiotic stress by qRT-PCR. Results. 65 JmjC genes were identified from B. napus genome, 29 from B. rapa, and 23 from B. oleracea. These genes were grouped into seven clades base on the phylogenetic analysis, and their catalytic activities of demethylation were predicted. The average retention rate of B. napus JmjC genes (B. napus JmjC gene from B. rapa (93.1%) and B. oleracea (82.6%)) exceeded whole genome level. JmjC sequences demonstrated high conservation in domain origination, chromosomal location, intron/exon number and catalytic sites. The gene duplication events were confirmed among the homologs. Furthermore, BrKDM5 subfamily genes were examined under stress conditions. A lot of BrKDM5 subfamily genes show higher expression under drought and NaCl treatment, but only a few genes are involved in high temperature stress. Conclusions. This study provides the first genome-wide characterization of JmjC genes in Brassica species. The BnJmjC exhibits higher conservation during the formation process of allotetraploid than the average retention rates of whole B. napus genome. Furthermore, expression profiles indicated that BnKDM5 subfamily genes are involved in stress response to salt, drought and high temperature. Cao X. 2016. REF6 recognizes a specific DNA sequence to demethylate H3K27me3 and regulate organ boundary formation in