Evaluation of Genetic and Epigenetic Modification in Rapeseed(Brassica napus)Induced by Salt Stress

Salinity is an important limiting environmental factor for rapeseed production worldwide.In this study,we assessed theextent and pattern of DNA damages caused by salt stress in rapeseed plants.Amplified fragment length polymorphism(AFLP)analysis revealed dose-related increases in sequence alterations in plantlets exposed to 10-1000 mmol/L sodiumchloride.In addition,individual plantlets exposed to the same salt concentration showed different AFLP and selected regionamplified polymorphism banding patterns.These observations suggested that DNA mutation in response to salt stress wasrandom in the genome and the effect was dose-dependant.DNA methylation changes in response to salt stress were alsoevaluated by methylation sensitive amplified polymorphism(MSAP).Three types of MSAP bands were recovered.Type Ⅰbands were observed with both isoschizomers HpaⅡand MspⅠ,while typeⅡand typeⅢbands were observed only withHpaⅡand MspⅠ,respectively.Extensive changes in types of MSAP bands after NaCl treatments were observed,includingappearance and disappearance of type Ⅰ,ⅡandⅢbands,as well as exchanges between either typeⅠand typeⅡor typeⅠand typeⅢbands.An increase of 0.2-17.6% cytosine methylated CCGG sites were detected in plantlets exposed to 10-200 mmol/L salt compared to the control,and these changes included both de novo methylation and demethylation events.Nine methylation related fragments were also recovered and sequenced,and one sharing a high sequence homologywith the ethylene responsive element binding factor was identified.These results demonstrated clear DNA genetic andepigenetic alterations in plantlets as a response to salt stress,and these changes may suggest a mechanism for plantsadaptation under salt stress.