Analysis of Genetic Variation and DNA Methylation Alteration in Autotetraploid and Diploid Rice

DNA methylation plays an important role in regulating the process of growth and development in eukaryotes.The purpose is to investigate the genome and methylation differences between diploid and tetraploid,explore the genetic differences and genomic DNA methylation level and pattern changes.The diploid and autotetraploid rices Gang 46B,Minghui63,R725,Chenghui149,Haitian and Shixiang were analyzed by SSR and MSAP technique.The results showed that most genomes of the autotetraploid and diploid rice were the same except some sites with three pair of primers preferably polymorphic and specific bands amplified in the different ploidy rice.The consequences of MSAP suggested that the total methylation ratio in autotetraploid rice(24.0%) was significantly less than the diploid rice(28.15%);The full methylation ratio and hemimethylation ratio were different between the autotetraploid and diploid rices.The averaged full methylation rate and hemimethylation rate were 6.24% and 22.03%,respectively for diploid rice,7.44% and 16.61% for autotetraploid rice.The degree of methylation did not increase due to polyploidy,indicating that diploid and tetraploid DNA methylation of the same species of rice changed.The pattern changes of the DNA methylation in the rice of various ploidy was further analyzed,which showed that demethylation occurred in autotetraploid rice on an average of about 11.6% sites,methylations on about 24.11% sites,and the proportion of genes with methylation significantly higher than that with demethylation.The methylation of some functional genes could induce gene silencing to ease the impact of genome doubling dose effect.