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，部分学者认为多倍化是向无融合生殖转变的必要前提。然而，由于多数无融合生殖多倍体为异源多倍体（allopolyploids），无融合生殖与多倍化之间的因果关联变得复杂，这使得部分学者推测，是杂交而非多倍化促成了无融合生殖的发生。二倍体无融合生殖为分离杂交的作用提供了罕见契机，目前在十字花科（Brassicaceae）弯叶南芥属（Boechera）中已记录到多种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有多样性的二倍体个体开展微卫星（microsatellite）分析，旨在验证"弯叶南芥属二倍体无融合生殖类群均为杂交起源"这一假说。本项全属范围的数据集能够得以构建，得益于核心微卫星位点可适用于70种弯叶南芥属二倍体物种中的69种，同时我们也成功对不同保存时长的标本馆标本（herbarium specimen）完成了基因分型。除极少数例外外，二倍体无融合生殖类群均表现出极高水平的杂合性（heterozygosity），这源于其差异性基因组的结合。该结果强烈表明，多数弯叶南芥属二倍体无融合生殖谱系均为杂交起源，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。