Data from: Does hybridization drive the transition to asexuality in diploid Boechera?

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（gametophytic apomixis）是植物中常见的无性繁殖形式。几乎所有配子体无融合生殖类群均为多倍体（polyploids），部分学者将多倍性视为向无融合生殖转变的必要前提。然而，由于大多数无融合生殖多倍体均为异源多倍体（allopolyploids），这一事实使得无融合生殖与多倍性之间的因果联系变得复杂，因而有学者推测，是杂交而非多倍性促成了无融合生殖的产生。二倍体无融合生殖（diploid apomixis）为分离杂交的作用提供了罕见的研究契机，目前已在Boechera属（十字花科Brassicaceae）中记录到多个二倍体无融合生殖类群。本研究针对1393份形态与地理分布均具多样性的二倍体个体开展微卫星（microsatellite）分析，对“二倍体Boechera无融合生殖类群为杂交起源”这一假说进行验证。该覆盖全属的数据集得以构建，得益于一套核心微卫星位点可在70个二倍体Boechera物种中的69个中通用，以及我们成功对不同保存时长的标本馆标本进行基因分型的能力。除少数例外情况外，二倍体无融合生殖类群均表现出极高水平的杂合性，该杂合性源于不同源基因组的结合。这一结果强烈表明，大多数无融合生殖的二倍体Boechera演化支均为杂交起源，且杂交带来的基因组效应促成了该属向配子体无融合生殖的转变。