Although the transition to selfing in the model plant Arabidopsis thaliana involved the loss of the self-incompatibility (SI) system, it clearly did not occur due to the fixation of a single inactivating mutation at the locus determining the specificities of SI (the S-locus). At least three groups of divergent haplotypes (haplogroups), corresponding to ancient functional S-alleles, have been maintained at this locus, and extensive functional studies have shown that all three carry distinct inactivating mutations. However, the historical process of loss of SI is not well understood, in particular its relation with the last glaciation. Here, we took advantage of recently published genomic resequencing data in 1,083 Arabidopsis thaliana accessions that we combined with BAC sequencing to obtain polymorphism information for the whole S-locus region at a species-wide scale. The accessions differed by several major rearrangements including large deletions and interhaplogroup recombinations, forming a set of haplogroups that are widely distributed throughout the native range and largely overlap geographically. “Relict” A. thaliana accessions that directly derive from glacial refugia are polymorphic at the S-locus, suggesting that the three haplogroups were already present when glacial refugia from the last Ice Age became isolated. Interhaplogroup recombinant haplotypes were highly frequent, and detailed analysis of recombination breakpoints suggested multiple independent origins. These findings suggest that the complete loss of SI in A. thaliana involved independent self-compatible mutants that arose prior to the last Ice Age, and experienced further rearrangements during postglacial colonization.
展开▼
机译:尽管模式植物拟南芥向自交的过渡涉及自交不亲和 (SI) 系统的丧失,但由于在决定 SI 特异性的位点(S 位点)上固定了单个失活突变,因此显然没有发生。至少有三组不同的单倍型(单倍群),对应于古老的功能性S等位基因,已经维持在该位点上,广泛的功能研究表明,这三组都携带不同的失活突变。然而,SI丧失的历史过程尚不清楚,特别是它与末次冰期的关系。在这里,我们利用最近发表的 1,083 份拟南芥种质的基因组重测序数据,并将其与 BAC 测序相结合,在物种范围内获得整个 S 位点区域的多态性信息。这些种质的不同之处在于几个主要的重排,包括大缺失和单倍群间重组,形成了一组单倍群,这些单倍群广泛分布在整个原生范围内,并且在地理上在很大程度上重叠。直接来源于冰川避难所的“遗迹”拟南芥种质在S位点是多态的,这表明当最后一个冰河时代的冰川避难所被分离出来时,这三个单倍群已经存在。单倍群间重组单倍型非常频繁,对重组断点的详细分析表明存在多个独立的起源。这些发现表明,拟南芥中SI的完全丧失涉及在最后一个冰河时代之前出现的独立的自相容突变体,并在冰期后定殖期间经历了进一步的重排。
展开▼