The Relationship Between DNA Methylation Difference And Heterosis In Flue-Cured Tobacco Varieties And Its F₁

DNA methylation plays an important role in gene expression regulation during growth and development in eukaryotes. To realize the relationship of the heterosis of flue-cured tobacco and DNA methylation, predict heterosis tobacco F1 to promote strong advantage breeding hybrids, this study uses NCⅡ design method to nine flue-cured tobacco varieties(lines) group with a 19 crosses, the main growth period of tobacco on F1 and yield traits parents were dynamically determined to explore the parental and F1 heterosis performance were screened of the hybrids yield traits specific advantages. And on the level of DNA methylation, we analyzed the relationship between DNA methylation and flue-cured tobacco hybrid traits and heterosis. The main results are as follows:1. There was a general heterosis in flue-cured tobacco. The high of heterosis changed with agronomic traits and materials. And the result of dynamic change showed that leaf length, leaf area and leaf number were growth fastest during transplanting 30-45 days, plant height was growth fastest during transplanting 45-60 days, leaf width was growth fastest during transplanting 15-45 days.2. The MSAP ratios, which were the ratios of MSAP sites to the totally amplified sites, in flue-cured tobacco varieties and F1 were 31.4 %~69.2 %. The average of MSAP, full methylation levels and hemi-methylation were 55.5 %, 28.9 % and 26.6%. Both MSAP and full methylation levels in most of the hybrid were higher than either of their parent, however, some of the hemi-methylation was lower than either of their parent.3. Five classes of MSAP patterns, A, B, C, D and E, among 19 flue-cured tobacco hybrids and their parents were detected: Pattern A, methylation levels were not changed in both parents and F1; Pattern B, demethylation, both or one of the parent was methylated,but no methylation in the same site in F1; Pattern C,hypermethylation, the methylation level in F1 was higher than those in both parents; Pattern D, hypomethylation, methylation in F1 was lower than those in both parents; Pattern E, methylation increases, methylation in F1 was higher than those in both parents. And pattern C was dominate. Thus indicates the increasing of the methylation in hybrids. Pattern B and D imply reducing in hybrids which ratio is 44.2 %. Comparing parent and F1 found that DNA methylation was changed in hybrid which was to balance the different methylation coming from parents. What’s more, the greater the difference in parents, the greater the adjustment in F1. It suggest that selecting parents is a very important for producing hybrid.4. By the F1 generation’s pattern of the methylated inheritance, we found that 20.9 % from matemal lines, howere, 23.4 % from patemal lines which indieated that the F1 inherit came from patemal lines more than matemal lines.5. Choosing significantly negative correlation both between the pattern of the methylated inheritance and heterosis which exited in the heterosis screened 5 specific locuses. Those were in primer H2-2, H4-2, H8-1, H8-2 amplification loci at 350 bp, 300 bp, 135 bp, 275 bp, 450 bp, respectively. The above results showed that specific loci could regulate and control the heterosis to make it express, and could impact the growth of leaf number.6. According to DNA methylation and heterosisof correlation analysis of the seedling stage and mature stage, there were some same significance level: full methylation and the leaf length heterosis, hemi-methylation and heterosis of leaf width;Methylation pattern A and the number of leaf phenotype, pattern B and leaf area and leaf length heterosis, pattern D and leaf length, leaf width, leaf number and leaf area of phenotype or heterosis, pattern E and leaf number of phenotype;Ha2 and leaf width and leaf area of phenotype and heterosis, Hb1 and leaf number of phenotypes, Hc1 and leaf width and leaf number of phenotypes.This suggests that the performance of heterosis have certain consistency, which can be through the detection of DNA methylation in seedling stage to maturity heterosis prediction.However, in seedling stage and mature stage and methylation significant were inconsistency, suggests that genomic methylation research should be carried out in terms of dynamic, different development stage has some different genes work on heterosis, need in multiple times by the viewpoint of dynamic analysis to study relationship between methylation and heterosis. As can be seen from the above results, although the MSAP was not associated with the heterosis, However, some specific loci have a significant effects on heterosis happened in the methylation types. Methylation might have sites with low levels of heterosis, and some sites methylation level enhancement to more positive heterosis.