Study On The Relationship Of DNA Methylation With Heterosis In Oilseed Rape

Utilization of heterosis has been to an important approach to increase crop yields since it was successfully used to improve seed yield in corn in the 1930s.However,the mechanisms of heterosis have remained poorly understood so far.Since 1980s,the evidences from molecular studies proved the possibility to reveal its mechanism.For example,the differential gene expression was detected between hybrid and parent.DNA methylation is considered to regulate the gene expression.In this study,the relationship of DNA methylation with heterosis was investigated.Main results were as follows.1.DNA methylation status on the whole genomeTen MSAP amplification primer combinations were used for the methylation analysis among crosses of B.napus with B.rapa,23 intraspecific crosses,together with 8 parental accessions in Brassica.Totally,177 polymorphic loci were detected from 252 clear recorded bands.2.Tissue Specificity of DNA methylationIt was found that the methylation level in seedling was higher than bud among 53 materials,and that parents exhibited high ratio of alternations of DNA methylation than hybrids at the seedling stage,but not significantly differed each other at the bud stage(p=0.49)Alternations of DNA methylation,hypomethylation and hypermethlation,were found from seedling to bud.The proporation of hypomethylation was higher than hypermethylation,except for the intraspecific hybrids of B.napus.The principle component analysis for the methylation alternation from seedling to bud revealed three groups.One group contained the B.napus parents and their intraspecific hybrids,while another one contained the B.rapa parents and their intraspecific hybrids.The third group was composed of the interspecific hybrids or B.napus and B.rapa.3.Differential methylation patterns among hybrids and parentsFour types of methylation patterns were detected among the tested accessions,the common band patterns in the hybrid and its both parents refered as A type(P1=P2=F1),the common band patterns in the hybrids and its female parents refered as type B(P1=F1≠P2),the common band patterns in the hybrids and its male parents refered as type C(P2=F1≠P1),the new band refered as type D,in which it differ between hybrid and parents(F1≠P1,P2).About 67.9%of band patterns belonged to the classification of type A,B and C.Among band patterns of D type,the degree of hypomethylation among all the accessions tested was higher than that of hypermethlation in seedling,while the degree of hypomethylation among the interspecific hybrids was higher than hypermethlation and the degree of hypomethylation among the interapecific hybrids was lower than hypermethlation.4.Analysis on agronomic traitsSeven agronomic traits related to heterosis,containing plant height,height of primary branch,length of main inflorescence,number of effective pods of the main inflorescence,number of effective pods per plant, number of seeds per pod and the number of primary branches,were tested in this study.Hybrids were better than relative parental accessions in the plant height,the length of main inflorescence,the number of effective pods of the main inflorescence and the yields.ANOVA analysis showed significant differents between parents and hybrids for plant height,height of primary branch,number of effective pods of the main inflorescence,number of effective pods per plant and number of seed per pod(p=0.01).5.Relationships of DNA methylated with heterosisThe loci significally relative to heterosis were selected by ANOVA analysis for plant height,length of main inflorescence,number of effective pods of the main inflorescence and biomass.All of methylation patterns in F1(P1=P1=F1,P1=F1≠P2,P2=F1≠P1,hypomethylation,hypermethlation and other patterns) were related to heterosis by calculating the effects of band patterns.