Hybridization is a central mechanism in evolution, producing new species or introducing important genetic variation into existing species. In plant-pathogenic fungi, adaptation and specialization to exploit a host species are key determinants of evolutionary success. Here, we performed experimental crosses between the two pathogenic Microbotryum species, M. lychnidis-dioicae and M. silenes-acaulis that are specialized to different hosts. The resulting offspring were analyzed on phenotypic and genomic levels to describe genomic characteristics of hybrid offspring and genetic factors likely involved in host-specialization. Genomic analyses of interspecific fungal hybrids revealed that individuals were most viable if the majority of loci were inherited from one species. Interestingly, species-specific loci were strictly controlled by the species’ origin of the mating type locus. Moreover we detected signs of crossing over and chromosome duplications in the genomes of the analyzed hybrids. In Microbotryum, mitochondrial DNA was found to be uniparentally inherited from the a2 mating type. Genome comparison revealed that most gene families are shared and the majority of genes are conserved between the two species, indicating very similar biological features, including infection and pathogenicity processes. Moreover, we detected 211 candidate genes that were retained under host-driven selection of backcrossed lines. These genes and might therefore either play a crucial role in host specialization or be linked to genes that are essential for specialization. The combination of genome analyses with experimental selection and hybridization is a promising way to investigate host-pathogen interactions. This study manifests genetic factors of host specialization that are required for successful biotrophic infection of the post-zygotic stage, but also demonstrates the strong influence of intra-genomic conflicts or instabilities on the viability of hybrids in the haploid host-independent stage.

中文翻译：

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Microbotryum 杂交后代的减数分裂重组及其对致病性的影响。


杂交是进化的核心机制，产生新物种或将重要的遗传变异引入现有物种。在植物病原真菌中，利用宿主物种的适应和专门化是进化成功的关键决定因素。在这里，我们在两种致病性微葡萄属物种 M. lychnidis-dioicae 和 M. silenes-acaulis 之间进行了实验杂交，它们专门针对不同的宿主。对所得后代进行表型和基因组水平分析，以描述杂交后代的基因组特征和可能涉及宿主特化的遗传因素。对种间真菌杂种的基因组分析表明，如果大多数基因座遗传自一个物种，那么个体的生存能力最强。有趣的是，物种特异性基因座受到物种交配型基因座起源的严格控制。此外，我们在分析的杂交体的基因组中检测到了交叉和染色体重复的迹象。在 Microbotryum 中，线粒体 DNA 被发现是从 a2 交配型单亲遗传的。基因组比较显示，两个物种之间大多数基因家族是共享的，并且大多数基因是保守的，这表明两个物种的生物学特征非常相似，包括感染和致病过程。此外，我们检测到 211 个候选基因在宿主驱动的回交系选择下被保留。因此，这些基因可能在宿主特化中发挥关键作用，或者与特化所必需的基因相关。基因组分析与实验选择和杂交相结合是研究宿主-病原体相互作用的一种有前途的方法。 这项研究表明了宿主特化的遗传因素，这是合子后阶段成功生物营养感染所需的，但也证明了基因组内冲突或不稳定性对单倍体宿主独立阶段杂种生存能力的强烈影响。