State Key Laboratory of Microbial Technology, Microbiology Technology Institute, Shandong Universitygrid.27255.37, Qingdao, People's Republic of China.
Microbiol Spectr. 2022 Aug 31;10(4):e0087222. doi: 10.1128/spectrum.00872-22. Epub 2022 Jul 19.
The expression of cellulase genes in lignocellulose-degrading fungus Trichoderma reesei is induced by insoluble cellulose and its soluble derivatives. Membrane-localized transporter/transceptor proteins have been thought to be involved in nutrient uptake and/or sensing to initiate the subsequent signal transduction during cellulase gene induction. Crt1 is a sugar transporter proven to be essential for cellulase gene induction although the detailed mechanism of Crt1-triggered cellulase induction remains elusive. In this study, we focused on the C-terminus region of Crt1 which is predicted to exist as an unstructured cytoplasmic tail in . Serial C-terminal truncation of Crt1 revealed that deleting the last half of the C-terminal region of Crt1 hardly affected its transporting activity or ability to mediate the induction of cellulase gene expression. In contrast, removal of the entire C-terminus region eliminated both activities. Of note, Crt1-C5, retaining only the first five amino acids of C-terminus, was found to be capable of transporting lactose but failed to restore cellulase gene induction in the Δ strain. Analysis of the cellular localization of Crt1 showed that Crt1 existed both at the plasma membrane and at the periphery of the nucleus although the functional relevance is not clear at present. Finally, we showed that the cellulase production defect of Δ was corrected by overexpressing Xyr1, indicating that Xyr1 is a potential regulatory target of the signaling cascade initiated from Crt1. The lignocellulose-degrading fungus has been widely used in industrial cellulases production. Understanding the precise cellulase gene regulatory network is critical for its genetic engineering to enhance the mass production of cellulases. As the key membrane protein involved in cellulase expression in , the detailed mechanism of Crt1 in mediating cellulase induction remains to be investigated. In this study, the C-terminal region of Crt1 was found to be vital for its transport and signaling receptor functions. These two functions are, however, separable because a C-terminal truncation mutant is capable of sugar transporting but loses the ability to mediate cellulase gene expression. Furthermore, the key transcriptional activator Xyr1 represents a downstream target of the Crt1-initiated signaling cascade. Together, our research provides new insights into the function of Crt1 and further contributes to the unveiling of the intricate signal transduction process leading to efficient cellulase gene expression in .
纤维素酶基因在木质纤维素降解真菌里氏木霉中的表达受不溶性纤维素及其可溶性衍生物诱导。膜定位的转运蛋白/感受蛋白被认为参与营养物质的摄取和/或感应，以启动纤维素酶基因诱导过程中的后续信号转导。Crt1 是一种已被证明对纤维素酶基因诱导至关重要的糖转运蛋白，尽管 Crt1 触发纤维素酶诱导的详细机制仍不清楚。在这项研究中，我们专注于 Crt1 的 C 端区域，该区域预测在细胞质中存在无结构的尾部。Crt1 的连续 C 端截断表明，删除 Crt1 的 C 端区域的后半部分几乎不会影响其转运活性或介导纤维素酶基因表达诱导的能力。相比之下，去除整个 C 端区域则消除了这两种活性。值得注意的是，保留 C 端前 5 个氨基酸的 Crt1-C5 能够运输乳糖，但不能恢复Δ菌株中的纤维素酶基因诱导。Crt1 的细胞定位分析表明，Crt1 既存在于质膜上，也存在于核的外围，尽管目前其功能相关性尚不清楚。最后，我们表明，通过过表达 Xyr1 可以纠正Δ的纤维素酶产生缺陷，表明 Xyr1 是 Crt1 起始信号级联的潜在调节靶标。木质纤维素降解真菌 已广泛用于工业纤维素酶的生产。了解精确的纤维素酶基因调控网络对于其遗传工程以提高纤维素酶的大规模生产至关重要。作为纤维素表达中涉及的关键膜蛋白，Crt1 介导纤维素诱导的详细机制仍有待研究。在这项研究中，Crt1 的 C 端区域对于其转运和信号受体功能至关重要。然而，这两个功能是可分离的，因为 C 端截断突变体能运输糖，但失去介导纤维素基因表达的能力。此外，关键转录激活因子 Xyr1 代表 Crt1 启动的信号级联的下游靶标。总之，我们的研究为 Crt1 的功能提供了新的见解，并进一步揭示了导致里氏木霉中高效纤维素酶基因表达的复杂信号转导过程。
