Effect Of SO₂ Exposure On DNA Methylation Polymorphism In Arabiadopsis Thaliana

Sulfur dioxide (SO2) as a common air pollutant, is great harmful effect to the living beings. SO2 exposure can affect the normal physiological activities of plants, high concentrations of SO2 can cause leaf chlorosis or necrosis, and inhibition of cell division, or even results in some cell to death. At present, the stress resistance of plants to SO2 exposure molecular mechanism have not been reported.In this paper, the method of methylation-sensitive amplified polymorphism (MSAP) was used to analyse the DNA methylation polymorphism levels in Arabidopsis thaliana whole genome after exposure to 30 mg/m3 SO2. The results showed that, total of 760 fragments were identified by 13 primer combinations. Obtained with the type, including three types of non-methylated, hemimethylated and fully methylated. In the SO2-fumigation group and the control group, non-methylation (Ⅰ-band) was most loci, respectively, the total amplification of polymorphic loci methylation were 55.66% and 53.29%, hemimethylated (Ⅲ-band) rates were 18.02% and 11.05%, full methylation (ⅡandⅣ-bands) rates were 26.32% and 35.66%, methylation-sensitive amplified polymorphism (MSAP) rates were 44.34% and 46.71%.409 fragments were shared by all the samples in the two conditions, with the methylation status of 53.82%. It was shown that 351 consistent fragments appeared different comparing with those control condition after exposure to SO2. DNA methylation in Arabidopsis genome polymorphism was 46.18%. Comparing with the control condition, the 220 fragments appeared to be methylated in SO2 condition, accounting for 28.95% PCR loci, and the 131 fragments appeared to be demethylated, of the total loci amplified by 17.23%. In the amplified fragments, methylated fragments were more than demethylation fragments, and the occurrence of hypermethylation sites (137) were more than the number of re-methylated sites (68). The results showed that SO2-fumigation process based on Arabidopsis genome DNA methylation level and pattern of DNA changes in the apparent genetic variation. The overall results showed that SO2 expose could induce the pattern of methylation in Arabidopsis.The method combining methylation sensitive restriction endonucleases with PCR (MSRE-PCR) was also used to analysis the methylation status of the first CCGG fragments in 5'coding regions of four SO2-response genes in Arabidopsis thaliana. The results showed that the coding regions of CCGG sites of MHL1 and NIT2 genes were full methylation of 5mCCGG in the control group and 30 mg/m3 of SO2-fumigation group, and the site of MYB was hemimethylation of 5mCCGG; the cytosine methylation states had no change after exposure to SO2. The coding region of CCGG site of ACS6 was non-methylation in the control group, while it was changed into hemimethylation of 5mCCGG after exposure to SO2. These results indicated that SO2 exposure can change the cytosine methylation of genes coding region in plant, which may contribute to genome stability and gene transcriptional regulation.