Aguayo Jaime, Halkett Fabien, Husson Claude, Nagy Zoltán Á, Szigethy András, Bakonyi József, Frey Pascal, Marçais Benoit
ANSES, Laboratoire de la Santé des Végétaux, Unité de Mycologie, Malzéville, France.
UMR IAM, INRA, Université de Lorraine, Nancy, France.
Appl Environ Microbiol. 2016 Nov 21;82(24):7142-7153. doi: 10.1128/AEM.02221-16. Print 2016 Dec 15.
Assessing the process that gives rise to hybrid pathogens is central to understanding the evolution of emerging plant diseases. Phytophthora ×alni, a pathogen of alder, results from the homoploid hybridization of two related species, Phytophthora uniformis and Phytophthora ×multiformis Describing the genetic characteristics of P ×alni should help us understand how reproductive mechanisms and historical processes shaped the population structure of this emerging hybrid pathogen. The population genetic structure of P ×alni and the relationship with its parental species were investigated using 12 microsatellites and one mitochondrial DNA (mtDNA) marker on a European collection of 379 isolates. Populations of P ×alni were dominated by one multilocus genotype (MLG). The frequency of this dominant MLG increased after the disease emergence together with a decline in diversity, suggesting that it was favored by a genetic mechanism such as drift or selection. Combined microsatellite and mtDNA results confirmed that P ×alni originated from multiple hybridization events that involved different genotypes of the progenitors. Our detailed analyses point to a geographic structure that mirrors that observed for P. uniformis in Europe. The study provides more insights on the contribution of P. uniformis, an invasive species in Europe, to the emergence of Phytophthora-induced alder decline.
Our study describes an original approach to assess the population genetics of polyploid organisms using microsatellite markers. By studying the parental subgenomes present in the interspecific hybrid P. ×alni, we were able to assess the geographical and temporal structure of European populations of the hybrid, shedding new light on the evolution of an emerging plant pathogen. In turn, the study of the parental subgenomes permitted us to assess some genetic characteristics of the parental species of P. ×alni, P. uniformis, and P ×multiformis, which are seldom sampled in nature. The subgenomes found in P. ×alni represent a picture of the "fossilized" diversity of the parental species.
评估产生杂交病原体的过程对于理解新出现的植物病害的进化至关重要。桤木疫霉（Phytophthora ×alni）是桤木的一种病原体，它由两个相关物种——均匀疫霉（Phytophthora uniformis）和多形疫霉（Phytophthora ×multiformis）的同倍体杂交产生。描述桤木疫霉的遗传特征应有助于我们理解生殖机制和历史过程如何塑造了这种新出现的杂交病原体的种群结构。我们使用12个微卫星标记和一个线粒体DNA（mtDNA）标记，对欧洲收集的379个桤木疫霉分离株进行研究，以调查桤木疫霉的种群遗传结构及其与亲本物种的关系。桤木疫霉种群以一种多位点基因型（MLG）为主。这种优势MLG的频率在病害出现后增加，同时多样性下降，这表明它受到了诸如遗传漂变或选择等遗传机制的青睐。微卫星和mtDNA的综合结果证实，桤木疫霉起源于涉及祖代不同基因型的多次杂交事件。我们的详细分析指出了一种地理结构，这种结构与在欧洲观察到的均匀疫霉的地理结构相似。该研究为欧洲的入侵物种均匀疫霉对疫霉引起的桤木衰退的出现所起的作用提供了更多见解。
我们的研究描述了一种使用微卫星标记评估多倍体生物种群遗传学的原始方法。通过研究种间杂交种桤木疫霉中存在的亲本亚基因组，我们能够评估该杂交种欧洲种群的地理和时间结构，为一种新出现的植物病原体的进化提供了新的线索。反过来，对亲本亚基因组的研究使我们能够评估桤木疫霉的亲本物种均匀疫霉和多形疫霉的一些遗传特征，这些物种在自然界中很少被采样。在桤木疫霉中发现的亚基因组代表了亲本物种“僵化”的多样性图景。
