Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun, Jilin Province, China.
PLoS One. 2013 Apr 16;8(4):e61995. doi: 10.1371/journal.pone.0061995. Print 2013.
Grafting has been extensively used to enhance the performance of horticultural crops. Since Charles Darwin coined the term "graft hybrid" meaning that asexual combination of different plant species may generate products that are genetically distinct, highly discrepant opinions exist supporting or against the concept. Recent studies have documented that grafting enables exchanges of both RNA and DNA molecules between the grafting partners, thus providing a molecular basis for grafting-induced genetic variation. DNA methylation is known as prone to alterations as a result of perturbation of internal and external conditions. Given characteristics of grafting, it is interesting to test whether the process may cause an alteration of this epigenetic marker in the grafted organismal products.
METHODOLOGY/PRINCIPAL FINDINGS: We analyzed relative global DNA methylation levels and locus-specific methylation patterns by the MSAP marker and locus-specific bisulfite-sequencing in the seed plants (wild-type controls), self- and hetero-grafted scions/rootstocks, selfed progenies of scions and their seed-plant controls, involving three Solanaceae species. We quantified expression of putative genes involved in establishing and/or maintaining DNA methylation by q-(RT)-PCR. We found that (1) hetero-grafting caused extensive alteration of DNA methylation patterns in a locus-specific manner, especially in scions, although relative methylation levels remain largely unaltered; (2) the altered methylation patterns in the hetero-grafting-derived scions could be inherited to sexual progenies with some sites showing further alterations or revisions; (3) hetero-grafting caused dynamic changes in steady-state transcript abundance of genes encoding for a set of enzymes functionally relevant to DNA methylation.
CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that inter-species grafting in plants could produce extensive and heritable alterations in DNA methylation. We suggest that these readily altered, yet heritable, epigenetic modifications due to interspecies hetero-grafting may shed one facet of insight into the molecular underpinnings for the still contentious concept of graft hybrid.
嫁接已被广泛用于提高园艺作物的性能。自从查尔斯·达尔文创造了“嫁接杂种”一词，意思是不同植物物种的无性组合可能产生在遗传上不同的、高度不同的产物以来，支持或反对这一概念的观点存在很大分歧。最近的研究记录表明，嫁接使嫁接伙伴之间能够交换 RNA 和 DNA 分子，从而为嫁接诱导的遗传变异提供了分子基础。DNA 甲基化由于内外条件的干扰而容易发生改变。鉴于嫁接的特点，有趣的是要测试该过程是否会导致嫁接生物体产物中这种表观遗传标记的改变。
方法/主要发现：我们通过 MSAP 标记和基于亚硫酸氢盐的测序分析了种子植物（野生型对照）、自交和异交接穗/砧木、接穗的自交后代及其种子植物对照的相对全基因组 DNA 甲基化水平和位点特异性甲基化模式，涉及 3 种茄科植物。我们通过 q-(RT)-PCR 定量分析了参与建立和/或维持 DNA 甲基化的假定基因的表达。我们发现：(1) 异交以一种特定于位点的方式引起了 DNA 甲基化模式的广泛改变，尤其是在接穗中，尽管相对甲基化水平基本保持不变；(2) 异交衍生的接穗中的改变的甲基化模式可以遗传给有性后代，一些位点显示出进一步的改变或修正；(3) 异交引起了一组与 DNA 甲基化功能相关的酶的编码基因的稳定转录物丰度的动态变化。
结论/意义：我们的结果表明，植物中的种间嫁接可以产生广泛的、可遗传的 DNA 甲基化改变。我们认为，由于种间异交而产生的这些易于改变但可遗传的表观遗传修饰可能为仍有争议的嫁接杂种概念提供分子基础的一个方面的见解。
