Effects of cadmium stress on DNA methylation in soybean

Abstract

Epigenetics plays an important role in plant resistance to biotic and abiotic stresses, although few studies have focused on soybean epigenetics associated with cadmium stress. In this study, hydroponically grown soybean seedlings were treated with hydroponic nutrient solution containing various concentrations of CdCl2 (0.5, 5, 15 mg L−1) to investigate the effects of cadmium exposure on soybean genomic DNA methylation levels and patterns using methylation-sensitive amplified polymorphism (MSAP) analysis. Overall, the results revealed alterations of genomic DNA methylation levels and patterns in soybean seedlings under cadmium stress, with methylation level and methylation polymorphism rate both increasing in a dose-dependent manner with increasing cadmium concentration. The total methylation rates for genomic DNA of control (CK), S1 (0.5 mg L−T CdCl2), S2 (5 mg L−1 CdCl2) and S3 (15 mg L−1 CdCl2) groups were 27.92%, 29.78%, 33.2% and 35.79%, respectively, and methylation polymorphism rates were 14.46%, 16.57% and 18.15%, respectively. Thus, soybean cadmium stress-induced methylation changes mainly reflected increased genomic DNA methylation. After polymorphic methylated genomic DNA fragments were recovered from polyacrylamide gels, cloned and sequenced, sequence homology comparisons revealed that among 30 detected differentially methylated fragments, 15 sequences were highly homologous to genes encoding functional proteins already known to be associated with plant stress responses. These results indicate that soybean resists cadmium stress by increasing both the level of genomic DNA methylation and the genomic DNA remethylation rate. This work provides a methodological foundation for investigating molecular mechanisms underlying the soybean response to cadmium stress.