Lineage-specific gene duplication and expansion of DUF1216 gene family in Brassicaceae

Proteins containing domain of unknown function (DUF) are prevalent in eukaryotic genome. The DUF1216 proteins possess a conserved DUF1216 domain resembling to the mediator protein of Arabidopsis RNA polymerase II transcriptional subunit-like protein. The DUF1216 family are specifically existed in Brassicaceae, however, no comprehensive evolutionary analysis of DUF1216 genes have been performed. We performed a first comprehensive genome-wide analysis of DUF1216 proteins in Brassicaceae. Totally 284 DUF1216 genes were identified in 27 Brassicaceae species and classified into four subfamilies on the basis of phylogenetic analysis. The analysis of gene structure and conserved motifs revealed that DUF1216 genes within the same subfamily exhibited similar intron/exon patterns and motif composition. The majority members of DUF1216 genes contain a signal peptide in the N-terminal, and the ninth position of the signal peptide in most DUF1216 is cysteine. Synteny analysis revealed that segmental duplication is a major mechanism for expanding of DUF1216 genes in Brassica oleracea, Brassica juncea, Brassica napus, Lepidium meyneii, and Brassica carinata, while in Arabidopsis thaliana and Capsella rubella, tandem duplication plays a major role in the expansion of the DUF1216 gene family. The analysis of Ka/Ks (non-synonymous substitution rate/synonymous substitution rate) ratios for DUF1216 paralogous indicated that most of gene pairs underwent purifying selection. DUF1216 genes displayed a specifically high expression in reproductive tissues in most Brassicaceae species, while its expression in Brassica juncea was specifically high in root. Our studies offered new insights into the phylogenetic relationships, gene structures and expressional patterns of DUF1216 members in Brassicaceae, which provides a foundation for future functional analysis.