Data from: Differential introgression and reorganization of retrotransposons in hybrid zones between wild wheats

The maintenance of species integrity despite pervasive hybridization is ruled by the interplay between reproductive barriers. Endogenous postzygotic isolation will shape the patterns of introgression in hybrid zones, leading to variable outcomes depending on the genetic mechanism involved. Here, we analysed experimental and natural hybrid populations of Aegilops geniculata and Aegilops triuncialis to examine the genetics of species boundaries in the face of gene flow. Because long-terminal repeat retrotransposons (LTR-RTs) showing differential evolutionary trajectories are probably to affect hybrid dysgenesis and reproductive isolation between these wild wheat species, we addressed the impact of LTR-RTs in shaping introgression between them. Experimental settings involving artificial sympatry and enforced crossings quantified strong, but incomplete reproductive isolation, and highlighted asymmetrical endogenous postzygotic isolation between the two species. Natural hybrid zones located in the northern Golan Heights were analysed using plastid DNA, amplified fragment length polymorphisms (AFLP) marking random sequences, and sequence-specific amplified polymorphisms (SSAP) tracking insertions from six LTR-RT families. This analysis demonstrated asymmetrical introgression and genome reorganization. In comparison with random sequences and quiescent LTR-RTs, those LTR-RTs predicted to be activated following conflicting interactions in hybrids revealed differential introgression across the hybrid zones. As also reported for synthetic F1 hybrids, such LTR-RTs were specifically reorganized in the genomes of viable hybrids, confirming that conflicts between selfish LTR-RTs may represent key incompatibilities shaping species boundaries and fostering long-term species integrity in the face of gene flow.

尽管普遍存在杂交现象，物种完整性的维持由各类生殖隔离屏障的相互作用所调控。内源性合子后生殖隔离会塑造杂交带内的基因渐渗模式，进而依据所涉及的遗传机制产生多样化的结果。本研究对具芒山羊草（Aegilops geniculata）与三芒山羊草（Aegilops triuncialis）的实验及自然杂交种群展开分析，以探究基因流背景下物种边界的遗传学基础。由于呈现差异化进化轨迹的长末端重复序列逆转录转座子（long-terminal repeat retrotransposons, LTR-RTs）可能影响这两类野生小麦近缘物种间的杂种劣生与生殖隔离，因此我们针对LTR-RTs在二者基因渐渗塑造过程中的影响开展研究。
设置包含人工同域种群与强制杂交的实验体系，量化得到了强烈但并不完全的生殖隔离，并揭示了两个物种间不对称的内源性合子后生殖隔离。对位于戈兰高地北部的自然杂交带进行分析时，本研究采用了质体DNA、用于标记随机序列的扩增片段长度多态性（amplified fragment length polymorphisms, AFLP），以及用于追踪6个LTR-RTs家族插入位点的序列特异性扩增片段多态性（sequence-specific amplified polymorphisms, SSAP）。该分析结果证实了不对称基因渐渗与基因组重排现象的存在。相较于随机序列与处于静息状态的LTR-RTs，那些被预测会在杂种内发生冲突互作后被激活的LTR-RTs，在各杂交带中呈现出差异化的基因渐渗模式。正如合成F1杂种的相关研究报道所言，这类LTR-RTs在可存活杂种的基因组中发生了特异性重排，这证实自私性LTR-RTs之间的冲突，可能是塑造物种边界、并在基因流存在的条件下维持物种长期完整性的关键不相容因素。