The ability of fungal cells to undergo cell-to-cell communication and anastomosis, the process of vegetative hyphal fusion, allows them to maximize their overall fitness. Previous studies in a number of fungal species have identified the requirement of several signaling pathways for anastomosis, including the so far best characterized soft (So) gene, and the MAPK pathway components MAK-1 and MAK-2 of Neurospora crassa. Despite the observations of hyphal fusions’ involvement in pathogenicity and host adhesion, the connection between cell fusion and fungal lifestyles is still unclear. Here, we address the role of anastomosis in fungal development and asexual reproduction in Zymoseptoria tritici, the most important fungal pathogen of wheat in Europe. We show that Z. tritici undergoes self-fusion between distinct cellular structures, and its mechanism is dependent on the initial cell density. Contrary to other fungi, cell fusion in Z. tritici only resulted in cytoplasmic mixing but not in multinucleated cell formation. The deletion of the So orthologous ZtSof1 disrupted cell-to-cell communication affecting both hyphal and germling fusion. We show that Z. tritici mutants for MAPK-encoding ZtSlt2 (orthologous to MAK-1) and ZtFus3 (orthologous to MAK-2) genes also failed to undergo anastomosis, demonstrating the functional conservation of this signaling mechanism across species. Additionally, the ΔZtSof1 mutant was severely impaired in melanization, suggesting that the So gene function is related to melanization. Finally, we demonstrated that anastomosis is dispensable for pathogenicity, but essential for the pycnidium development, and its absence abolishes the asexual reproduction of Z. tritici. We demonstrate the role for ZtSof1, ZtSlt2, and ZtFus3 in cell fusions of Z. tritici. Cell fusions are essential for different aspects of the Z. tritici biology, and the ZtSof1 gene is a potential target to control septoria tritici blotch (STB) disease.

中文翻译：

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营养细胞融合在小麦真菌病原体小麦枯萎病菌的发育和无性繁殖中的作用。

真菌细胞经过细胞间通讯和吻合的能力，即植物菌丝融合的过程，可以使它们的整体适应能力最大化。先前在许多真菌物种中的研究已经确定了用于吻合的几种信号传导途径的需求，其中包括迄今为止表征最好的软基因（So），以及神经孢霉的MAPK途径组分MAK-1和MAK-2。尽管观察到菌丝融合参与了致病性和宿主粘附，但细胞融合与真菌生活方式之间的联系仍不清楚。在这里，我们探讨了Zymoseptoria tritici（欧洲最重要的小麦真菌病原体）中真菌在真菌发育和无性繁殖中的吻合作用。我们显示Z. tritici经历了不同细胞结构之间的自融合，其机制取决于初始细胞密度。与其他真菌相反，小麦在小麦中的融合仅导致细胞质混合，而不导致多核细胞形成。Sotologous ZtSof1的删除破坏了细胞之间的通信，影响了菌丝融合和幼芽融合。我们显示Z.tritici突变体的MAPK编码ZtSlt2（与MAK-1同源）和ZtFus3（与MAK-2同源）基因也未能进行吻合，这表明该信号机制在物种间的功能保守性。此外，ΔZtSof1突变体的黑色素化受到严重损害，这表明So基因功能与黑色素化有关。最后，我们证明了吻合术对于致病性是必不可少的，但对于脓毒症的发展却是必不可少的，它的缺失消除了Z. tritici的无性繁殖。我们展示了ZtSof1，ZtSlt2和ZtFus3在小麦的Z.tritici细胞融合中的作用。细胞融合对于小麦Z.tritici生物学的各个方面都是必不可少的，并且ZtSof1基因是控制小麦棕褐色斑点病（STB）的潜在靶标。