Microevolution of fungal plant parasites by means of adaptation to host and climate - a case study using the Acacia rust genus Ravenelia

大多数主要作物病害都是由稻瘟菌、咖啡锈病或大豆锈病等真菌植物寄生虫引起的。然而，除了对农业的破坏性影响外，在更自然的生态系统中，它们被认为在维持寄主植物的遗传多样性方面发挥着重要作用。在对两个伙伴之间潜在的遗传相互作用进行分子分析方面，寄主-寄生虫相互作用是研究最多的系统之一。但尽管如此，对宿主与寄生虫相互作用的进化还知之甚少。一些真菌，如锈菌或黑穗病真菌，由于密切的共同进化而被讨论了强烈的寄主专一性，但到目前为止，似乎有几种相互竞争的理论可以解释这些观察到的寄主-寄生虫分布模式，但缺乏一个包罗万象的解释。虽然许多研究侧重于共同进化在并行进化方面的长期影响，但迫切需要更好地了解生物(宿主基因)和非生物因素(例如气候条件)在塑造宿主-寄生虫相互作用的进化结果方面的差异效应。因此，在拟议的项目中，我们的目标是利用群体遗传学方法来揭示寄主专一性和气候对南非相思锈菌微观进化的影响。锈菌Ravenelia macowaniana侵染了金合欢属的两个不同树种。分布在南非的两个不同的气候区域，两个孤立地区的过渡将这两个栖息地联系在一起。在两个寄主物种的主要分布范围内进行循环抽样设计，将使我们能够区分对种群水平的不同影响。我们将使用在不同地区两个寄主物种上收集的四个样本的低覆盖率基因组测序来开发高度可变的微卫星标记，用于种群遗传分析。基于对24个种群的密集抽样，我们想要分析寄主或环境对植物病原菌基因的影响较大。对比环境中寄主树种的分离和重叠种群的实验设置旨在允许对这两种情况进行单独和组合的解释。因此，我们的项目将提供有关寄主特有的植物寄生虫在自然环境中进化的基本信息。这将使我们能够更好地理解物种形成、宿主转移和共同进化等微观进化过程，我们的结果也可以作为农业和林业的模型。

Most of the major crop diseases are caused by fungal plant parasites like rice blast fungus, coffee rust or soybean rust. However, besides their destructive effects in agriculture, in more natural ecosystems they are supposed to play important roles in maintaining genetic diversity of their host plants. Host-parasite interactions are among the most studied systems in terms of molecular analysis of the underlying genetic interactions between the two partners. But still, the evolution of host-parasite interactions is only poorly understood. The strong host specificity of some fungi like the rust or smut fungi have been discussed as a result of close coevolution, but so far it seems that several competing theories can explain these observed patterns of host-parasite distribution with similar support and an all-embracing explanation is lacking. While many studies have focused on the long-term effects of coevolution in terms of parallel evolution, the a better understanding of the differential effects of biotic (host genotype) and abiotic factors (e.g. climatic conditions) in shaping the evolutionary outcome of a host-parasite interaction is urgently needed. Thus, in the proposed project we aim to disentangle the influence of host specificity and climate on the microevolution of an Acacia-rust in South Africa using a population genetics approach. The rust fungus Ravenelia macowaniana infects two distinct tree species of the genus Vachellia (Acacia s.l.) distributed in two different climatic regions in South Africa, where both habitats are linked by transition in two isolated localities. A circular sampling design spanning both host species in their major distribution ranges will allow us to separate the different effects on the population level.We will use low coverage genome sequencing of four specimens of Ravenelia macowaniana collected on both host species in distinct regions to develop highly variable microsatellite markers for a population genetic analysis. Based on a dense sampling of 24 populations in total we want to analyse whether the host or the environment exert the higher impact on a plant pathogens genotype. The experimental setup of separated as well as overlapping populations of host tree species in contrasting environments is designed to allow an interpretation with respect to both scenarios, separately and combined. Thus, our project will provide basic information on the evolution of host specific plant parasites in a natural environment. This will allow understanding microevolutionary processes like speciation, host shifts and coevolution much better and our results could serve as a model for agriculture and forestry as well.