不同倍性西瓜基因组DNA甲基化水平与模式的MSAP分析

DNA甲基化是表观遗传修饰的主要方式之一，在基因表达调控中发挥重要作用。本研究以不同倍性（2x、3x、4x）西瓜为试材，采用基于DNA甲基化敏感酶的扩增多态性分析（Methylation-Sensitive Ampliftcation Polymorphism，MSAP）方法，在全基因组水平上探究西瓜同源多倍化过程中DNA序列中CCGG位点的甲基化水平及模式变化特征。研究中选用23对选扩引物，共检测到1883个基因位点。二倍体、三倍体、四倍体中检测到的位点数分别为647、655和581；其中发生甲基化的位点数分别为181、150和159。相应的扩增总甲基化率分别为28．0％、22．9％和27．4％：全甲基化位点数分别为121、80和82，相应的全甲基化率分别为18．7％、12．2％和14．1％。进一步对不同倍性西瓜DNA甲基化模式的变化特征进行分析，结果显示：四倍体西瓜与二倍体西瓜相比有超过半数的位点（54．4％）DNA甲基化模式发生了变化，其与三倍体西瓜相比也有近一半的位点（45．4％）DNA甲基化模式发生了变化，并且变化趋势都以四倍体西瓜甲基化程度升高为主：而三倍体西瓜与二倍体西瓜相比．虽然也有41．6％的位点DNA甲基化模式发生了改变，但变化趋势以三倍体西瓜甲基化程度降低略占优势：与之相似，三倍体西瓜与四倍体相比较。甲基化的变化趋势也是以三倍体西瓜甲基化程度降低为主。以上结果表明：不同倍性西瓜中DNA甲基化事件虽均有发生．但不论是从总甲基化率还是全甲基化率来看，DNA甲基化水平与倍性高低关系不大．三倍体西瓜表现出较为显著的低甲基化水平特征。DNA甲基化模式的分析也表明。与二倍体及四倍体西瓜相比．三倍体西瓜DNA甲基化模式的调整主要以去甲基化为主。显示出三倍体西瓜基因组独特的DNA甲基化特征。本研究为进一步从表观遗传学的角度探讨西瓜的三倍体优?

ANALYSIS OF THE LEVEL AND PATTERN OF GENOMIC DNA METHYLATION IN DIFFERENT PLOIDY WATERMELONS BY MSAP(Citrullus lanatus )

DNA methylation is one of the major epigenetic modifications. It is very important to the regulation of gene expression. In present study, an autoploidy series （2x, 3x and 4x） in watermelon （Citrullus lanatus ） was constructed and MSAP （Methylation-Sensitive Amplification Polymorphism） analysis was conducted to elucidate the level and pattern of DNA methylation at CCGG sites in different ploidy watermelons. Totally, 1 883 genetic loci were produced by 23 pairs of selective primers, of which 647, 655 and 581 sites were detected in diploid, autotriploid and autotetraploid, respectively. The methylation sites were 181, 150 and 159, and the corresponding total methylation ratios were 28.0%, 22.9% and 27.4% in 2x, 3x and 4x, respectively, of which the fully methylation sites were 121, 80 and 82, and the corresponding fully methylation 18.7%, 12.2% and 14.1%. Further analysis of the pattern of DNA methylation suggested ratios were that compared 4x with 2x, about half of detected sites （54.4%） shown changes of DNA methylation patterns. Similarly, compared 4x with 3x, 45.4% sites also shown changes of DNA methylation patterns. Moreover, the trend of DNA methylation adjustment mainly involved increase of DNA methylation levels in 4x. However, compared 3x with 2x or 4x, although the changes of DNA methylation pattern also widely occurred, which involved 41.6% （compared 3x with 2x） and 45.4% （compared 3x with 4x） sites, respectively, the trend of DNA methylation adjustment mainly involved decrease of DNA methylation levels in 3x. All these results indicated that DNA methylation events were widely existed in different ploidy watermelons. However, not only based on the total DNA methylation ratio or fully DNA methylation ratio, the results both implied that the DNA methylation levels were not closely associated with the autopolyploidy level in watermelon. Autotriploid watermelon shows obvious low level of DNA methylation. Analysis of DNA methylation patterns also suggested that the adjustment of DNA