Conservation and diversity of the regulators of cellulolytic enzyme genes in Ascomycete fungi

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 .