Plant Breeding, Wageningen University and Research, 6708 PB Wageningen, The Netherlands.
Plant Breeding, Wageningen University and Research, 6708 PB Wageningen, The Netherlands
Genetics. 2019 Jan;211(1):263-276. doi: 10.1534/genetics.118.301566. Epub 2018 Nov 6.
Interspecific crosses can result in progeny with reduced vitality or fertility due to genetic incompatibilities between species, a phenomenon known as hybrid incompatibility (HI). HI is often caused by a bias against deleterious allele combinations, which results in transmission ratio distortion (TRD). Here, we determined the genome-wide distribution of HI between wild lettuce, , and cultivated lettuce, , in a set of backcross inbred lines (BILs) with single introgression segments from introgressed into a genetic background. Almost all BILs contained an introgression segment in a homozygous state except a few BILs, for which we were able to obtain only a single heterozygous introgression. Their inbred progenies displayed severe TRD with a bias toward the allele and complete nontransmission of the homozygous introgression, , absolute HI. These HI might be caused by deleterious heterospecific allele combinations at two loci. We used an multilocus segregating interspecific F2 population to identify candidate conspecific loci that can nullify the HI in BILs. Segregation analysis of developed double-introgression progenies showed nullification of three HI and proved that these HI are explained by nuclear pairwise incompatibilities. One of these digenic HI showed 29% reduced seed set and its pattern of TRD pointed to a sex-independent gametophytic barrier. Namely, this HI was caused by complete nontransmission of one heterospecific allele combination at the haploid stage, surprisingly in both male and female gametophytes. Our study shows that two-locus incompatibility systems contribute to reproductive barriers among species.
种间杂交可能导致后代活力或繁殖力下降，这是由于物种间的遗传不兼容性，即杂种不兼容性 (HI)。HI 通常是由于对有害等位基因组合的偏见导致的，这导致了传递率扭曲 (TRD)。在这里，我们在一组回交自交系 (BIL) 中确定了野生生菜和栽培生菜之间的全基因组 HI 分布，这些 BIL 具有来自 的单个渐渗片段， 被导入到 的遗传背景中。除了少数 BIL 外，几乎所有 BIL 都含有纯合状态的渐渗片段，而这些 BIL 我们只能获得单个杂合渐渗片段。它们的自交后代表现出严重的 TRD，偏向 等位基因，并且纯合的 渐渗物完全不传递，绝对 HI。这些 HI 可能是由两个位点的有害异源等位基因组合引起的。我们使用多基因分离的种间 F2 群体来鉴定可以消除 BIL 中 HI 的同型等位基因位点。开发的双渐渗后代的分离分析表明，有三个 HI 被消除，并证明这些 HI 是由核双等位基因不兼容性引起的。其中一个双基因 HI 表现出 29%的种子结实减少，其 TRD 模式指向非依赖于性别的配子体障碍。也就是说，这种 HI 是由于在单倍体阶段完全不传递一种异源等位基因组合引起的，令人惊讶的是，在雄性和雌性配子体中都存在这种情况。我们的研究表明，两个基因座不兼容性系统有助于物种间的生殖障碍。
