Functional Characterization of Sugar Transporter CRT1 Reveals Differential Roles of Its C-Terminal Region in Sugar Transport and Cellulase Induction in Trichoderma reesei.
Functional Characterization of Sugar Transporter CRT1 Reveals Differential Roles of Its C-Terminal Region in Sugar Transport and Cellulase Induction in Trichoderma reesei.
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DOI：
10.1128/spectrum.00872-22
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发表时间：
2022-08-31
影响因子：
3.7
通讯作者：
Liu, Weifeng
中科院分区：
文献类型：
--
作者：
Wang, Zhixing;Yang, Renfei;Lv, Wenhao;Zhang, Weixin;Meng, Xiangfeng;Liu, Weifeng
不溶性纤维素及其可溶性衍生物诱导木质纤维素降解菌里氏木霉纤维素酶基因的表达。膜定位的转运蛋白/受体蛋白被认为参与了纤维素酶基因诱导过程中的营养吸收和/或传感，以启动随后的信号转导。Crt 1是一种糖转运蛋白，被证明是纤维素酶基因诱导所必需的，尽管Crt 1触发纤维素酶诱导的详细机制仍然难以捉摸。在这项研究中，我们专注于Crt 1的C-末端区域，这被预测为存在于T. reesei。连续的C-末端截短的Crt 1表明，删除后一半的C-末端区域的Crt 1几乎不影响其转运活性或介导的诱导纤维素酶基因表达的能力。相反，去除整个C-末端区域消除了这两种活性。值得注意的是，Crt 1-C5，仅保留C-末端的前5个氨基酸，被发现能够运输乳糖，但不能恢复Δ crt 1菌株中纤维素酶基因的诱导。Crt 1的细胞定位分析表明，Crt 1既存在于质膜上，也存在于核周围，但其功能相关性目前尚不清楚。最后，我们发现Δ crt 1的纤维素酶生产缺陷通过过表达Xyr 1得到纠正，表明Xyr 1是Crt 1启动的信号级联的潜在调控靶点。木质纤维素降解真菌T.里氏木霉已广泛用于工业纤维素酶生产。了解纤维素酶基因的精确调控网络是进行纤维素酶基因工程以提高纤维素酶大规模生产的关键。作为T. reesei的研究，Crt 1介导纤维素酶诱导的详细机制仍有待研究。在这项研究中，发现Crt 1的C-末端区域对其转运和信号受体功能至关重要。然而，这两种功能是可分离的，因为C-末端截短突变体能够转运糖，但失去了介导纤维素酶基因表达的能力。此外，关键的转录激活因子Xyr 1代表了Crt 1启动的信号级联的下游靶标。总之，我们的研究为Crt 1的功能提供了新的见解，并进一步有助于揭示导致纤维素酶基因在T. reesei。
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 T. reesei. 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 Δcrt1 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 Δcrt1 was corrected by overexpressing Xyr1, indicating that Xyr1 is a potential regulatory target of the signaling cascade initiated from Crt1. IMPORTANCE The lignocellulose-degrading fungus T. reesei 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 T. reesei, 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 T. reesei.
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