The present study demonstrates that a nascent polypeptide-associated complex α subunit (Nac1) functions as a transcriptional regulator and plays both positive and negative roles in a vast array of functions in Alternaria alternata. Gain- and loss-of-function studies reveal that Nac1 is required for the formation and germination of conidia, likely via the regulation of Fus3 and Slt2 mitogen-activated protein kinase (MAPK)-coding genes, both implicated in conidiation. Nac1 negatively regulates hyphal branching and the production of cell wall-degrading enzymes. Importantly, Nac1 is required for the biosynthesis of siderophores, a novel phenotype that has not been reported to be associated with a Nac in fungi. The expression of Nac1 is positively regulated by iron, as well as by the Hog1 MAPK and the NADPH-dependent oxidase (Nox) complex. Nac1 confers cellular susceptibility to reactive oxygen species (ROS) likely via negatively regulating the expression of the genes encoding Yap1, Skn7, Hog1, and Nox, all involved in ROS resistance. The involvement of Nac1 in sensitivity to glucose-, mannitol-, or sorbitol-induced osmotic stress could be due to its ability to suppress the expression of Skn7. The requirement of Nac1 in resistance to salts is unlikely mediated through the transcriptional activation of Hog1. Although Nac1 plays no role in toxin production, Nac1 is required for fungal full virulence. All observed deficiencies can be restored by re-expressing a functional copy of Nac1, confirming that Nac1 contributes to the phenotypes. Thus, a dynamic regulation of gene expression via Nac1 is critical for developmental, physiological, and pathological processes of A. alternata.

中文翻译：

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新生多肽相关复合亚基α在铁轮菌中铁载体生物合成，氧化应激反应和毒力中的作用。

本研究表明，新生的多肽相关复合物α亚基（Nac1）充当转录调节因子，并在链格孢菌的多种功能中发挥正负作用。功能获得和功能丧失的研究表明，分生孢子的形成和萌发需要Nac1，这可能是通过调节Fus3和Slt2丝裂原活化蛋白激酶（MAPK）编码基因的调控而实现的，这两个基因都与分生孢子有关。Nac1负调节菌丝分支和细胞壁降解酶的产生。重要的是，Nac1是铁载体生物合成所必需的，铁载体是一种新的表型，尚未报道与真菌中的Nac有关。Nac1的表达受铁，Hog1 MAPK和NADPH依赖性氧化酶（Nox）复合物正调控。Nac1可能通过负面调节编码Yap1，Skn7，Hog1和Nox的基因表达来赋予细胞对活性氧（ROS）的敏感性，而这些基因均与ROS抗性有关。Nac1对葡萄糖，甘露醇或山梨醇诱导的渗透压敏感的参与可能是由于其抑制Skn7表达的能力。Nac1对盐的抗性需求不太可能通过Hog1的转录激活来介导。尽管Nac1在毒素产生中不起作用，但真菌充分的毒力需要Nac1。可以通过重新表达Nac1的功能性拷贝来恢复所有观察到的缺陷，从而确认Nac1有助于表型。因此，通过Nac1的基因表达的动态调节对于交替链球菌的发育，生理和病理过程至关重要。