The Preliminary Study About DNA Methylation Polymorphisms And Genetic Stability In Parents Of Hybrid Rice

The genetic variation forming by differences of DNA sequences has been widely studied and used in breeding ever since the time of Mendel. Non-DNA sequence variations, such as DNA methylation and histone modification, can also change biological traits such as plant height, flowering time, resistance and yield. Those variations can be inherited stably. As an important epigenetic modification, DNA methylation presents in many species of animals and plants, regulating gene expression, cell differentiation, genomic imprinting and system development. However, the researches before were concerning about the genetic improvement of varieties, the basic scientific questions such as DNA methylation polymorphism, genetic stability and biological functions were not clear. In this study, we selected a total of 62 hybrid rice as research materials, including restorer, maintainer line, sterile line, F1 hybrid and F2 segregation population. MSAP was employed to analyze DNA methylation modification. The cytoplasm and environment impact on methylation were also analyzed. This study aimed at exploring the application of DNA methylation in breeding and hoped to propose a new strategy of breeding selection from methylation alleles. The results were as follows:The methylation polymorphisms among parental lines. There were 1842 methylation sites of the 20 parental samples after amplification by 46 pairs of primers. The results showed that the methylation polymorphic loci reached 43.38% and monomorphic loci were 56.62% among the 20 parental lines. It indicated that methylation polymorphism among the parents was abundant and with good representation. The methylation clustering map, which was consistent with the pedigree relationships, directly showed the epigenetic distance among these 20 materials.The genetic stability of the methylation sites and the environmental impact on the methylation types. There were 148 methylation sites of the 40 parental samples after amplification by 4 pairs of primers. The ratio of the monomorphic type reached 77.6%, and the ratio of polymorphic ones was 22.4%. It showed that many methylated loci could be stably inherited, but with some exceptions which seemed be influenced by environments. The types with decreased methylation level were more than those with increased level. Those results indicated that environment could have impact on methylation types. Environmental changed DNA methylation, which subsequently affected the traits we observed.The analysis of DNA methylation among parents and its hybrid progenies. There were 257 methylation sites of the 23 samples after amplification by 6 pairs of primers. The results showed that there were more monomorphic methylation loci between parents and F1 generation. The similar phenomenon was observed from the F1 and F2 generations. The different methylation loci between parents were chose to analyze the genetic patterns in the offspring. The results showed that the specific methylation sites in the parents and offspring could be transmitted among generations, but further experiments were needed to verify the genetic of methylation sites.The impact of cytoplasmic genes on the methylation types. There were 884 methylation sites between the maintainer line Jinke 1B and sterile line Jinke 1A samples amplification by 27 pairs of primers. The analysis showed that the differences of methylation between the two types were only 8.03%, indicating that there was some influence of different cytoplasm on methylation types.