山核桃子代甲基化分析及其与薄壳山核桃甲基化的比较

Methylation Analysis of Half-sib Populations in Hickory and Comparison in Methylation between Hickory and Pecan

为了研究山核桃的遗传,本研究采用MSAP (Methylation sensitive amplification polymorphism)标记分析了山核桃30个半同胞子代群体及薄壳山核桃29个无性系,并在山核桃亲子代间及山核桃与薄壳山核桃间比较了遗传及甲基化水平。研究发现,山核桃半同胞子代群体非甲基化遗传位点(Non-methylation loci,NML)的比例较高,占33.69%,随后依次是内部胞嘧啶甲基化位点(15.18%)、半甲基化位点(9.25%);其遗传多样性(0.110 3±0.028 4)极显著地小于表观遗传多样性(0.568 5±0.112 3)(p<0.000 1);半同胞子代群体间存在显著的遗传与表观遗传分化,且大部分遗传变异和表观遗传变异存在于群体内,说明亲本间存在遗传差异。甲基化水平在山核桃亲子代间无显著差异(p>0.05),说明甲基化存在代际遗传。山核桃中NML的比例远大于薄壳山核桃,两物种表观遗传多样性相当,但薄壳山核桃的遗传多样性要高于山核桃;两物种遗传和表观遗传差异极显著(p<0.000 1),供试个体基于物种的遗传位点可以分别聚类,说明两物种各自个体间有遗传差异。甲基化敏感位点(Methylation-sensitive loci, MSL)及NML在两物种间存在极显著差异,且变异主要存在于物种内,两物种有明显的分化,但从各遗传参数值来讲,两物种又十分相像,正反交基于亲缘关系可行。不同于山核桃,薄壳山核桃遗传位点对甲基化位点影响极显著。

In order to study the genetic background of hickory(C.cathayensis),MSAP(Methylation sensitive amplification polymorphism)was used to analyze 30 half-sib populations of hickory and 29 clones of pecan(C.illino-ensis)and to compare the genetic and methylated levels between hickory parents and their offspring and between hickory and pecan at the level of species.It showed that the percentage of non-methylation genetic loci(NML)was high in the half-sib populations of hickory(33.69%),followed by internal cytosine methylated loci(15.18%)and hemi-methylated loci(9.25%).The genetic diversity(0.1103±0.0284)was overall significantly lower than the epigenetic diversity(0.5685±0.1123)in the half-sib populations(p<0.0001).Significant genetic and epigenetic differentiation existed among the half-sib populations,and most of the genetic and epigenetic variation existed within the populations,indicating the genetic difference exists among the hickory parents.There was no significant difference in methylation between hickory parents and their half-sib offspring(p>0.05),indicating that methylation is heritable between generations.The proportion of NML in hickory was far above that of pecan,and the epigenetic diversity between hickory and pecan was similar,but the genetic diversity of pecan was higher than that of hickory,and the genetic variation differed significantly from the epigenetic one in both species (p<0.000 1).Species-based individuals could be clustered respectively in terms of genetic loci,indicating that there are genetic differences among individuals of each species.The MSL(Methylation-sensitive loci)and NML of pecan were significantly different from those of hickory(p<0.000 1),and most of variation existed within the species,which indicates that two species are distinctively differentiated from each other.However,genetic parameters show that two species are very close and similar,which supports the feasibility of reciprocal crosses between pecan and hickory.Finally,the genetic background in pecan had a significant influence on its epigenetic variation,which is different from that in hickory.