Kunitake Emi, Kobayashi Tetsuo
Laboratory of Applied Microbiology, Department of Biological Mechanisms and Functions, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan.
Microbial Genetics Laboratory, Graduate School of Bioresources, Mie University, 1577 Kurimamachiya-cho, Tsu, 514-8507, Japan.
Curr Genet. 2017 Dec;63(6):951-958. doi: 10.1007/s00294-017-0695-6. Epub 2017 Apr 27.
In the past decade, various transcriptional activators of cellulolytic enzyme genes have been identified in Ascomycete fungi. The regulatory system of cellulolytic enzymes is not only partially conserved, but also significantly diverse. For example, Trichoderma reesei has a system distinct from those of Aspergillus and Neurospora crassa-the former utilizes Xyr1 (the Aspergillus XlnR ortholog) as the major regulator of cellulolytic enzyme genes, while the latter uses CLR-2/ClrB/ManR orthologs. XlnR/Xyr1 and CLR-2/ClrB/ManR are evolutionarily distant from each other. Regulatory mechanisms that are controlled by CLR-2, ClrB, and ManR are also significantly different, although they are orthologous factors. Expression of clr-2 requires the activation of another transcription factor, CLR-1, by cellobiose, while CLR-2 is constitutively active for transactivation. By contrast, ClrB activation requires cellobiose. While ClrB mainly regulates cellulolytic genes, ManR is essential for the activation of not only cellulolytic but also mannanolytic enzyme genes. In this review, we summarize XlnR/Xyr1- and CLR-2/ClrB/ManR-dependent regulation in N. crassa, A. nidulans, A. oryzae, and T. reesei and emphasize the conservation and diversity of the regulatory systems for cellulolytic enzyme genes in these Ascomycete fungi. In addition, we discuss the role of McmA, another transcription factor that plays an important role in recruiting ClrB to the promoters in A. nidulans.
在过去十年中，已在子囊菌中鉴定出多种纤维素分解酶基因的转录激活因子。纤维素分解酶的调控系统不仅部分保守，而且差异显著。例如，里氏木霉具有与曲霉和粗糙脉孢菌不同的系统——前者利用Xyr1（曲霉XlnR的直系同源物）作为纤维素分解酶基因的主要调控因子，而后者使用CLR-2/ClrB/ManR的直系同源物。XlnR/Xyr1和CLR-2/ClrB/ManR在进化上彼此相距甚远。由CLR-2、ClrB和ManR控制的调控机制也有显著差异，尽管它们是直系同源因子。clr-2的表达需要纤维二糖激活另一种转录因子CLR-1，而CLR-2在反式激活方面是组成型活性的。相比之下，ClrB的激活需要纤维二糖。虽然ClrB主要调节纤维素分解基因，但ManR不仅对纤维素分解酶基因的激活至关重要，而且对甘露聚糖分解酶基因的激活也必不可少。在本综述中，我们总结了粗糙脉孢菌、构巢曲霉、米曲霉和里氏木霉中XlnR/Xyr1和CLR-2/ClrB/ManR依赖性调控，并强调了这些子囊菌中纤维素分解酶基因调控系统的保守性和多样性。此外，我们还讨论了McmA的作用，McmA是另一种转录因子，在构巢曲霉中将ClrB募集到启动子中发挥重要作用。
