Asexual fungi include important pathogens of plants and other organisms, and their effective management requires understanding of their evolutionary dynamics. Genetic recombination is critical for adaptability and could be achieved via heterokaryosis — the co-existence of genetically different nuclei in a cell resulting from fusion of non-self spores or hyphae — and the parasexual cycle in the absence of sexual reproduction. Fusion between different strains and establishment of viable heterokaryons are believed to be rare due to non-self recognition systems. Here, we investigate the extent and mechanisms of cell fusion and heterokaryosis in the important asexual plant pathogen Verticillium dahliae. We used live-cell imaging and genetic complementation assays of tagged V. dahliae strains to analyze the extent of non-self vegetative fusion, heterokaryotic cell fate, and nuclear behavior. An efficient CRISPR/Cas9-mediated system was developed to investigate the involvement of autophagy in heterokaryosis. Under starvation, non-self fusion of germinating spores occurs frequently regardless of the previously assessed vegetative compatibility of the partners. Supposedly “incompatible” fusions often establish viable heterokaryotic cells and mosaic mycelia, where nuclei can engage in fusion or transfer of genetic material. The molecular machinery of autophagy has a protective function against the destruction of “incompatible” heterokaryons. We demonstrate an imperfect function of somatic incompatibility systems in V. dahliae. These systems frequently tolerate the establishment of heterokaryons and potentially the initiation of the parasexual cycle even between strains that were previously regarded as “incompatible.”

中文翻译：

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饥饿诱导的细胞融合和异核体经常逃避无性真菌病原体中不完美的同种异体识别系统

无性真菌包括植物和其他生物的重要病原体，它们的有效管理需要了解它们的进化动态。基因重组对于适应性至关重要，可以通过异核体（非自体孢子或菌丝融合导致细胞中遗传不同的细胞核共存）以及在没有有性生殖的情况下进行副性循环来实现。由于非自我识别系统，不同菌株之间的融合和可行异核体的建立被认为是罕见的。在这里，我们研究了重要的无性植物病原体黄萎病菌中细胞融合和异核的程度和机制。我们使用标记的 V. dahliae 菌株的活细胞成像和遗传互补分析来分析非自我营养融合的程度，异核细胞命运和核行为。开发了一种有效的 CRISPR/Cas9 介导的系统来研究自噬在异核体中的参与。在饥饿的情况下，无论先前评估的伴侣的营养相容性如何，都会经常发生发芽孢子的非自我融合。据称“不相容”的融合通常会建立可行的异核细胞和镶嵌菌丝体，其中细胞核可以参与融合或遗传物质的转移。自噬的分子机制具有防止“不相容”异核体破坏的保护功能。我们证明了 V. dahliae 中体细胞不相容系统的不完善功能。