Correlation Between DNA Methylation Polymorphism And Heterosis, And DNA Methylation Changes Induced By EMS-treatment

As an intrinsic allogamy crop, maize has an intricacy genetic basis. By hybridizing inbred lines which from controlled pollination to obtain heterosis has been widely used in maize. Further studying the heterotic phenomenon in maize may help understanding the mechanism of heterosis. In this thesis, we selected maize inbred lines from different heterotic groups in the spring district northeast China to explore possible correlations between the heterotic performance in yield and some related characters and genetic/epigenetic distance and the role DNA methylation played in heterosis by using AFLP/MSAP analysis. Major results obtained include:(1) Grain yield and related characters had MPH and BPH, especially grain yield in unit area and individual. The combinations those had good heterotic performances were from inbred lines early-maturing and late-maturing; Lancaster group and Reid group/ Lvda Red Cob Group.(2) The combination ability results showed that Dan340, Lvda Red Cob Group, had a high GCA in grain yield, and so as in the SCA analysis, suggest Dan340 may produce good combination that perform heterosis with other materials. The Effect Size that combination Mo17×Dan340, Qi318×Dan340 and 614×Dan340 had suggest Lvda Red Cob Group would have fine heterotic performance in combination with Lancaster Group and PN Group.(3) Given that epigenetic mechanisms may play a part in heterosis, we sought to probe for possible relationships between the parental epigenetic difference in the form of DNA methylation level revealed by the epigenetic marker MSAP among a set of 11 maize inbred lines and heterosis in four agronomic traits manifested by a set of 30 F1 hybrids resulting from a half-diallel crossing among the inbred lines. We found that a specific type of DNA methylation-level difference, i.e., relative CHG (H denotes A, C or T) methylation levels at the 5’-CCGG sites exhibits a statistically significant negative correlation with heterosis in the number of rows per ear (NRE) and a positive correlation with the number of kernels per row (NKR), whereas no correlation was detected between any of the DNA methylation-level differences and the rest two studied traits, 100-kernel weight (HKW) and kernel weight per ear (KWE). In a sharp contrast, parental genetic distance revealed by the genetic marker AFLP did not show any correlation with heterosis for any of the four studied agronomic traits.Our results suggest that parental epigenetic difference in particular types of DNA methylation- level difference plays some significant roles in the manifestation of heterosis of specific traits in maize, but the effects can be in opposite directions, and hence, offsetting each other culminating to cryptic effects on yield itself.Taken together, the results suggest the that epigenetic polymorphism in maize inbred lines, especially the difference in DNA methylation level, had certain significance in forecasting heterosis. The correlation between genetic distance and the number of kernel per row (NKR)/ the number of kernel per ear suggest epigenetic mechanism may regulate the heterosis.