Molecular basis and ecological genetics of hybrid incompatibilities involving a balanced NPR1 polymorphism in the genus Capsella

在物种形成过程中基因流障碍的建立是由Bateson-Dobzhansky-Muller模型描述的。根据这个模型，新的等位基因，成为固定在分离的群体中的负面相互作用，在杂交和降低他们的健身。在植物中，许多这样的不亲和性是多态性的，在物种或群体中存在相容和不相容的等位基因。这表明遗传漂变和/或平衡选择在杂种不亲和性形成中的重要作用。我们最近的特点是分子基础的多态性之间的不相容性的早期物种大花荠菜和C。风疹涉及两个病原体反应基因NPR 1和RPP 5。而不相容的RPP 5等位基因似乎是由C.风疹，相容和不相容的NPR 1等位基因在C. grandiflora;相反，C.风疹对于相容的NPR 1等位基因是固定的。这两个NPR 1等位基因在C. grandiflora的，可能反映了他们的功能专业化设置的病原体响应的基础水平。不同C. grandiflora和C.风疹加入，我们已经确定了三个更多的杂交不相容性涉及NPR 1和至少一个其他位点不同于RPP 5。这些研究结果表明，长期维护功能不同的等位基因，平衡选择和他们的分歧谱系排序促进早期物种之间的Bateson-Dobzhansky-Muller不相容性的建立。本项目将通过三个目标来研究涉及平衡NPR 1多态性的杂交不亲和性的分子基础和生态遗传学。(1)我们将确定不相容的RPP 5等位基因中的因果突变，并研究其对RPP 5和NPR 1之间相互作用的影响，以及其进化历史。(2)我们将确定其他不相容基因座的其他NPR 1依赖的不相容性之间的C。grandiflora和C.风疹，确定因果突变，并研究其进化史和群体遗传学。(3)在C.将通过表征在希腊中部的自然栖息地中采样的个体的叶和根相关微生物组来研究grandiflora;微生物组参数将与植物的NPR 1基因型相关联，以测试关于NPR 1平衡选择的不同假设。任何关联都将通过使用定义的微生物组组成的植物生长实验来跟踪。总之，这些研究将提供重要的新的洞察力的进化和生态遗传学的杂交不相容性，在荠菜，可能是相关的更广泛的植物物种形成与远系繁殖到自交的过渡。

The establishment of gene-flow barriers during speciation is described by the Bateson-Dobzhansky-Muller model of hybrid incompatibilities. According to this model, novel alleles that become fixed in separated populations interact negatively in hybrids and decrease their fitness. In plants, many such incompatibilities are polymorphic, with compatible and incompatible alleles present in the species or populations. This suggests an important role of genetic drift and/or balancing selection in the formation of hybrid incompatibilities. We have recently characterized the molecular basis of a polymorphic incompatibility between the incipient species Capsella grandiflora and C. rubella involving the two pathogen-response genes NPR1 and RPP5. While the incompatible RPP5 allele appears to have arisen by a novel mutation in C. rubella, both compatible and incompatible NPR1 alleles are present at high frequencies in C. grandiflora; by contrast, C. rubella is fixed for the compatible NPR1 allele. The two NPR1 alleles have been maintained by balancing selection in C. grandiflora, possibly reflecting their functional specialization in setting the basal level of pathogen response. From further crosses between different C. grandiflora and C. rubella accessions, we have identified three more hybrid incompatibilities involving NPR1 and at least one other locus distinct from RPP5. These findings suggest that the long-term maintenance of functionally divergent alleles by balancing selection and their divergent lineage sorting facilitate the establishment of Bateson-Dobzhansky-Muller incompatibilities between incipient species. This project will investigate the molecular basis and ecological genetics of hybrid incompatibilities involving the balanced NPR1 polymorphism by focussing on three objectives. (1) We will determine the causal mutation in the incompatible RPP5 allele and study its effect on the interaction between RPP5 and NPR1, as well as its evolutionary history. (2) We will identify the other incompatible loci for the additional NPR1-dependent incompatibilities between C. grandiflora and C. rubella, determine the causal mutations and study their evolutionary history and population genetics. (3) The basis of the observed balancing selection on NPR1 in C. grandiflora will be investigated by characterizing the leaf- and root-associated microbiome of individuals sampled in their natural habitat in Central Greece; microbiome-parameters will be associated with the NPR1 genotype of the plants to test different hypotheses about the balancing selection on NPR1. Any associations will be followed up by plant growth experiments using defined microbiome compositions. Together, these studies will provide important novel insight into the evolutionary and ecological genetics of hybrid incompatibilities in Capsella that are likely to be relevant more broadly to plant speciation associated with the outbreeding-to-selfing transition.