Yan Su, Xu Yan, Yu Xiao-Wei
Lab of Brewing Microbiology and Applied Enzymology, School of Biotechnology and Key Laboratory of Industrial Biotechnology of Ministry of Education, Jiangnan University, Wuxi, 214122, China.
Biotechnol Biofuels Bioprod. 2023 Jul 24;16(1):118. doi: 10.1186/s13068-023-02371-7.
Induction of cellulase in cellulolytic fungi Trichoderma reesei is strongly activated by cellulosic carbon sources. The transport of cellulosic inducer and the perception of inducing signal is generally considered as the critical process for cellulase induction, that the inducing signal would be perceived by a sugar transporter/transceptor in T. reesei. Several sugar transporters are coexpressed during the induction stage, but which function they serve and how they work collaboratively are still difficult to elucidate.
In this study, we found that the constitutive expression of the cellulose response transporter-like protein CRT2 (previously identified as putative lactose permease TRE77517) improves cellulase induction on a cellulose, cellobiose or lactose medium. Functional studies indicate that the membrane-bound CRT2 is not a transporter of cellobiose, lactose or glucose in a yeast system, and it also does not affect cellobiose and lactose utilization in T. reesei. Further study reveals that CRT2 has a slightly similar function to the cellobiose transporter CRT1 in cellulase induction. Overexpression of CRT2 led to upregulation of CRT1 and the key transcription factor XYR1. Moreover, overexpression of CRT2 could partially compensate for the function loss of CRT1 on cellulase induction.
Our study uncovers the novel function of CRT2 in cellulase induction collaborated with CRT1 and XYR1, possibly as a signal transductor. These results deepen the understanding of the influence of sugar transporters in cellulase production.
纤维素分解真菌里氏木霉中纤维素酶的诱导被纤维素碳源强烈激活。纤维素诱导物的转运和诱导信号的感知通常被认为是纤维素酶诱导的关键过程，即诱导信号会被里氏木霉中的一种糖转运蛋白/转ceptor感知。几种糖转运蛋白在诱导阶段共表达，但它们发挥何种功能以及如何协同工作仍难以阐明。
在本研究中，我们发现纤维素反应转运蛋白样蛋白CRT2（先前被鉴定为假定的乳糖通透酶TRE77517）的组成型表达可改善在纤维素、纤维二糖或乳糖培养基上的纤维素酶诱导。功能研究表明，膜结合的CRT2在酵母系统中不是纤维二糖、乳糖或葡萄糖的转运蛋白，并且它也不影响里氏木霉中纤维二糖和乳糖的利用。进一步研究表明，CRT2在纤维素酶诱导方面与纤维二糖转运蛋白CRT1具有略微相似的功能。CRT2的过表达导致CRT1和关键转录因子XYR1的上调。此外，CRT2的过表达可以部分补偿CRT1在纤维素酶诱导方面的功能丧失。
我们的研究揭示了CRT2在与CRT1和XYR1协同作用的纤维素酶诱导中的新功能，可能作为一种信号转导器。这些结果加深了对糖转运蛋白在纤维素酶生产中影响的理解。
