Identifying nutrients available in the environment and utilizing them in the most efficient manner is a challenge common to all organisms. The model filamentous fungus Neurospora crassa is capable of utilizing a variety of carbohydrates, from simple sugars to the complex carbohydrates found in plant cell walls. The zinc binuclear cluster transcription factor CLR-1 is necessary for utilization of cellulose, a major, recalcitrant component of the plant cell wall; however, expression of clr-1 in the absence of an inducer is not sufficient to induce cellulase gene expression. We performed a screen for unidentified actors in the cellulose-response pathway and identified a gene encoding a hypothetical protein (clr-3) that is required for repression of CLR-1 activity in the absence of an inducer. Using clr-3 mutants, we implicated the hyperosmotic-response pathway in the tunable regulation of glycosyl hydrolase production in response to changes in osmolarity. The role of the hyperosmotic-response pathway in nutrient sensing may indicate that cells use osmolarity as a proxy for the presence of free sugar in their environment. These signaling pathways form a nutrient-sensing network that allows N. crassa cells to tightly regulate gene expression in response to environmental conditions.

中文翻译：

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养分敏感通路网络和保守的激酶级联将渗透性和碳敏感结合在神经孢菌中

识别环境中可用的养分并以最有效的方式利用它们是所有生物共同面临的挑战。模型丝状真菌Neurospora crassa能够利用多种碳水化合物，从单糖到植物细胞壁中发现的复杂碳水化合物。锌双核簇转录因子CLR-1是利用纤维素（植物细胞壁的主要顽固成分）所必需的。然而，在没有诱导剂的情况下clr-1的表达不足以诱导纤维素酶基因表达。我们对纤维素反应途径中的身份不明的参与者进行了筛选，并鉴定了编码假设蛋白（clr-3），这是在没有诱导剂的情况下抑制CLR-1活性所必需的。使用clr-3突变体，我们将高渗反应途径牵涉到对渗透压变化的糖基水解酶生产的可调节调节中。高渗反应途径在营养物感测中的作用可能表明细胞使用渗透压作为其环境中游离糖存在的代理。这些信号传导途径形成了一个营养感应网络，允许N的传播。crassa细胞可根据环境条件严格调节基因表达。