Study On DNA Methylation And Gene Expression After Natural Autotriploidization Of SAR Ⅱ-628 Twin-seedling Rice (Oryza Sativa L.)

In recent years, the researches on evolution and gene expression of polyploid plants are going front of polyploid research fields. The main result from those studies was the rapid gene expression differentiation after polyploidization, including polymorphic expression-change patterns among individuals and among organs. Those researches focused on synthetic allopolyploid with even ploidy such as wheat, corn, brassica et al. Only a few case were made on autopolyploid such as in yeast and Arabidopsis; things were the same when it came to natural polyploid except such several recent allopolyploids as Spartina, Tragopogon and Senecio; Few researches were conducted on DNA methylation mutation and gene expression change of rice natural-genesic triploid. However, both of autopolyploid and rice polyploid are related to evolution, which should not be ignored in the research of polyploid evolution and gene expression.Autotriploids, occurring naturally from SARâ…¡-628 twin-seedling rice, was employed as research material in this study. Isoschizomers Hpaâ…¡ and MspⅠ　 were employed to analyze methylation mutation during triploidization; Gene chip, AFLP-cDNA and RT-PCR were combined together to analyze gene expression change during triploidization (haploid expression was also included in chip analysis). The results showed that rapid DNA methylation mutaion and rapid gene expression change emerged in M₀ generation after SARâ…¡-628 natural autotriploidization. The main results are as follows:Methylation mutation analysis: 1) The variation of methylation level, from 17.24% to 17.20%, was trivial after triploidization; 2) Among the 29 methylation mutated sites, the ratios of increase, decrease and undecision for methylation levels were 29.51%, 47.54% and 22.95%, respectively, which suggested that increased sites of methylation level were more than deceased ones; 3) Methylation mutaion sites distributed on the whole genome and were site-specific.Chip analysis: The chip data were checked from two aspects. That is, associated analysis of haploid, diploid and triploid, and analysis only with triploid. The results of associated analysis were as follows: 1) Most of the chromosomes had different sensitivities to ploidy change. That is, sites on some chromosomes had more tendencies for expression change; 2) Some ploidy-sensitive sites clustered together on chromosome; 3) Ploidy-sensitive sites had an uneven function distribution; 4) Change frequency of haploid was higher than that of triploid but with similar expression change amounts and function classes; 5) There were quite a number of silent and activated sites during both haploidization and triploidization. Activated and increased sites were more that silent and decreased ones; 6) Against genome dose effect, there was similar effect on the same gene during both haploidization and triploidization.