DNA methylation plays an important role in plant growth and development, and in regulating the activity of transposable elements (TEs).  Research on DNA methylation-related (DMR) genes has been reported in Arabidopsis, but little research on DMR genes has been reported in Brassica rapa and Brassica oleracea, the genomes of which exhibit significant differences in TE content.  In this study, we identified 78 and 77 DMR genes in Brassica rapa and Brassica oleracea, respectively.  Detailed analysis revealed that the numbers of DMR genes in different DMR pathways varied in B. rapa and B. oleracea.  The evolutionary selection pressure of DMR genes in B. rapa and B. oleracea was compared, and the DMR genes showed differential evolution between these two species.  The nucleotide diversity (π) and selective sweep (Tajima’s D) revealed footprints of selection in the B. rapa and B. oleracea populations.  Transcriptome analysis showed that most DMR genes exhibited similar expression characteristics in B. rapa and B. oleracea.  This study dissects the evolutionary differences and genetic variations of the DMR genes in B. rapa and B. oleracea, and will provide valuable resources for future research on the divergent evolution of DNA methylation between B. rapa and B. oleracea.

Whole genome duplication (WGD) and tandem duplication (TD) are important modes of gene amplification and functional innovation, and they are common in plant genome evolution.  We analyzed the genomes of three Solanaceae species (Solanum lycopersicum, Capsicum annuum, and Petunia inflata), which share a common distant ancestor with Vitis vinifera, Theobroma cacao, and Coffea canephora but have undergone an extra whole genome triplication (WGT) event.  The analysis was used to investigate the phenomenon of tandem gene evolution with (S. lycopersicum) or without WGT (V. vinifera).  Among the tandem gene arrays in these genomes, we found that V. vinifera, which has not experienced the WGT event, retained relatively more and larger tandem duplicated gene (TDG) clusters than the Solanaceae species that experienced the WGT event.  Larger TDG clusters tend to be derived from older TD events, so this indicates that continuous TDGs (absolute dosage) accumulated during long-term evolution.  In addition, WGD and TD show a significant bias in the functional categories of the genes retained.  WGD tends to retain dose-sensitive genes related to biological processes, including DNA-binding and transcription factor activity, while TD tends to retain genes involved in stress resistance.  WGD and TD also provide more possibilities for gene functional innovation through gene fusion and fission.  The TDG cluster containing the tomato fusarium wilt resistance gene I3 contains 15 genes, and one of these genes, Solyc07g055560, has undergone a fusion event after the duplication events.  These data provide evidence that helps explain the new functionalization of TDGs in adapting to environmental changes.