Department of Biology, Duke University, Durham, NC 27708, USA.
Evolution. 2012 Apr;66(4):985-95. doi: 10.1111/j.1558-5646.2011.01507.x. Epub 2011 Dec 8.
Gametophytic apomixis is a common form of asexual reproduction in plants. Virtually all gametophytic apomicts are polyploids, and some view polyploidy as a prerequisite for the transition to apomixis. However, any causal link between apomixis and polyploidy is complicated by the fact that most apomictic polyploids are allopolyploids, leading some to speculate that hybridization, rather than polyploidy, enables apomixis. Diploid apomixis presents a rare opportunity to isolate the role of hybridization, and a number of diploid apomicts have been documented in the genus Boechera (Brassicaceae). Here, we present the results of a microsatellite study of 1393 morphologically and geographically diverse diploid individuals, evaluating the hypothesis that diploid Boechera apomicts are hybrids. This genus-wide dataset was made possible by the applicability of a core set of microsatellite loci in 69 of the 70 diploid Boechera species and by our ability to successfully genotype herbarium specimens of widely varying ages. With few exceptions, diploid apomicts exhibited markedly high levels of heterozygosity resulting from the combination of disparate genomes. This strongly suggests that most apomictic diploid Boechera lineages are of hybrid origin, and that the genomic consequences of hybridization allow for the transition to gametophytic apomixis in this genus.
配子体无融合生殖是植物中一种常见的无性繁殖形式。实际上，所有的配子体无融合生殖都是多倍体，一些人认为多倍体是向无融合生殖转变的先决条件。然而，无融合生殖和多倍体之间的任何因果关系都很复杂，因为大多数无融合生殖的多倍体都是异源多倍体，这使得一些人推测，杂交而不是多倍体使无融合生殖成为可能。二倍体无融合生殖提供了一个难得的机会来分离杂交的作用，并且已经在拟南芥属（Brassicaceae）中记录了一些二倍体无融合生殖个体。在这里，我们报告了对 1393 个形态和地理上多样化的二倍体个体进行微卫星研究的结果，评估了二倍体拟南芥无融合生殖个体是杂种的假设。由于在 70 个二倍体拟南芥物种中的 69 个物种中应用了一组核心微卫星标记，以及我们成功对具有不同年龄的大量植物标本进行基因分型的能力，使得这个全属范围的数据成为可能。除了少数例外，二倍体无融合生殖个体表现出明显高水平的杂合性，这是由不同基因组的组合产生的。这强烈表明，大多数无融合生殖的二倍体拟南芥谱系是杂种起源的，并且杂交的基因组后果允许在这个属中向配子体无融合生殖转变。
