title: Intracellular β-glucosidases CEL1a and CEL1b are essential for cellulase induction on lactose in Trichoderma reesei.
abstract: Lactose (1,4-O-β-d-galacto-pyranosyl-d-glucose) induces cellulolytic enzymes in Trichoderma reesei and is in fact one of the most important soluble carbon sources used to produce cellulases on an industrial level. The mechanism underlying the induction is, however, not fully understood. In this study, we investigated the cellular functions of the intracellular β-glucosidases CEL1a and CEL1b in the induction of cellulase genes by lactose in T. reesei. We demonstrated that while CEL1a and CEL1b were functionally equivalent in mediating the induction, the simultaneous absence of these intracellular β-glucosidases abolished cbh1 gene expression on lactose. d-Galactose restored the efficient cellulase gene induction in the Δcel1a strain independently of its reductive metabolism, but not in the Δcel1a Δcel1b strain. A further comparison of the transcriptional responses of the Δcel1a Δcel1b strain complemented with wild-type CEL1a or a catalytically inactive CEL1a version and the Δcel1a strain constitutively expressing CEL1a or the Kluyveromyces lactis β-galactosidase LAC4 showed that both the CEL1a protein and its glycoside hydrolytic activity were indispensable for cellulase induction by lactose. We also present evidence that intracellular β-glucosidase-mediated lactose induction is further conveyed to XYR1 to ensure the efficiently induced expression of cellulase genes.
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan, Shandong, People's Republic of China.
authors.forename: Jintao
authors.initials: J
authors.lastname: Xu
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan, Shandong, People's Republic of China.
authors.forename: Guolei
authors.initials: G
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan, Shandong, People's Republic of China.
authors.forename: Yanbo
authors.initials: Y
authors.lastname: Kou
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan, Shandong, People's Republic of China.
authors.forename: Weixin
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Institute of Agro-Food Science Technology, Shandong Academy of Agricultural Sciences, Jinan, People's Republic of China.
authors.forename: Qingxin
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan, Shandong, People's Republic of China.
authors.forename: Guanjun
authors.initials: G
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan, Shandong, People's Republic of China weifliu@sdu.edu.cn.
authors.forename: Weifeng
authors.initials: W
authors.lastname: Liu
mesh_terms: D002480:Cellulase / Q000096:biosynthesis / Q000235:genetics*; D004790:Enzyme Induction; D005656:Fungal Proteins / Q000502:physiology*; D005690:Galactose / Q000378:metabolism; D055786:Gene Knockout Techniques; D006868:Hydrolysis; D007424:Intracellular Fluid / Q000201:enzymology; D007785:Lactose / Q000378:metabolism; D014158:Transcription, Genetic; D014242:Trichoderma / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D001617:beta-Glucosidase / Q000502:physiology*
chemical_list: D005656:Fungal Proteins; D001617:beta-Glucosidase; D002480:Cellulase; D007785:Lactose; D005690:Galactose