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。几乎所有的配子体无融合生殖物种均为多倍体，部分学者将多倍性视为向无融合生殖过渡的必要前提。然而，大多数无融合生殖多倍体均为异源多倍体，这一事实使得无融合生殖与多倍性之间的因果关联变得复杂，以至于部分学者推测，是杂交而非多倍性促成了无融合生殖的产生。二倍体无融合生殖为分离杂交的作用提供了难得的研究契机，十字花科（Brassicaceae）鼠耳芥属（Boechera）中已记录有多种二倍体无融合生殖类群。本研究对1393份形态与地理分布均具多样性的二倍体个体开展了微卫星（microsatellite）分析，以验证二倍体鼠耳芥属无融合生殖物种为杂交起源这一假说。得益于70个二倍体鼠耳芥属物种中的69个均可适用一套核心微卫星位点，且我们能够成功对不同保存时长的标本馆标本进行基因分型，本研究得以获取覆盖整个属级范围的数据集。除极少数例外情况外，二倍体无融合生殖个体均表现出极高水平的杂合性，该杂合性源于异源基因组的融合。这一结果强烈表明，大多数无融合生殖的二倍体鼠耳芥属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过渡。