Genome-Wide Identification and Evolutionary and Expression Analyses of the Cyclin B Gene Family in Brassica napus .

Cyclin B (CYCB) is a regulatory subunit of cyclin-dependent kinase (CDK), the concentration of which fluctuates to regulate cell cycle progression. Extensive studies have been performed on cyclins in numerous species, yet the evolutionary relationships and biological functions of the CYCB family genes in Brassica napus remain unclear. In this study, we identified 299 CYCB genes in 11 B . napus accessions. Phylogenetic analysis suggests that CYCB genes could be divided into three subfamilies in angiosperms and that the CYCB3 subfamily members may be a newer group that evolved in eudicots. The expansion of BnaCYCB genes underwent segmental duplication and purifying selection in genomes, and a number of drought-responsive and light-responsive cis -elements were found in their promoter regions. Additionally, expression analysis revealed that BnaCYCBs were strongly expressed in the developing seed and silique pericarp, as confirmed by the obviously reduced seed size of the mutant cycb3;1 in Arabidopsis thaliana compared with Col-0. This study provides a comprehensive evolutionary analysis of CYCB genes as well as insight into the biological function of CYCB genes in B . napus .