Genome-Wide Characterization and Analysis of Metallothionein Family Genes That Function in Metal Stress Tolerance in Brassica napus L.

Brassica plants exhibit both high biomass productivity and high rates of heavy metal absorption. Metallothionein (MT) proteins are low molecular weight, cysteine-rich, metal-binding proteins that play crucial roles in protecting plants from heavy metal toxicity. However, to date, MT proteins have not been systematically characterized in Brassica. In this study, we identified 60 MTs from Arabidopsis thaliana and five Brassica species. All the MT family genes from Brassica are closely related to Arabidopsis MTs, encoding putative proteins that share similar functions within the same clades. Genome mapping analysis revealed high levels of synteny throughout the genome due to whole genome duplication and segmental duplication events. We analyzed the expression levels of 16 Brassica napus MTs (BnaMTs) by RNA-sequencing and real-time RT-PCR (RT-qPCR) analysis in plants under As(3+) stress. These genes exhibited different expression patterns in various tissues. Our results suggest that BnaMT3C plays a key role in the response to As(3+) stress in B. napus. This study provides insight into the phylogeny, origin, and evolution of MT family members in Brassica, laying the foundation for further studies of the roles of MT proteins in these important crops.