The putative \u03b2-glucosidase BGL3I regulates cellulase induction in Trichoderma reesei

Gen Zou,Yanping Jiang,Zhihua Zhou,Zhihua Zhu,Rui Liu

doi:10.1186/s13068-018-1314-6

Abstract

BackgroundThe filamentous fungus Trichoderma reesei (anamorph of Hypocrea jecorina) displays increased cellulase expression while growing on inducers such as lactose or cellulose. However, the mechanism of cellulase induction in T. reesei is not yet completely characterized. Here, a protein annotated as β-glucosidase (BGL3I) was found to be involved in cellulase induction in T. reesei. The effects of BGL3I on cellulase production have not yet been fully understood.ResultsDeletion of the bgl3i gene had no influence on the growth of T. reesei, but significantly increased its cellulase activities. Deletion of bgl3i also resulted in decreased extracellular galactosidase activity, but significantly increased transcription of lactose permeases, which might be involved in lactose transport. Furthermore, deletion of bgl3i enhanced the transcription levels of intracellular β-glucosidases cel1a, cel1b and the regulator xyr1, which are all essential for lactose induction in T. reesei. BGL3I was found to have a relatively high ability to hydrolyze sophorose, which is proposed to be the strongest natural inducer of cellulase synthesis in T. reesei.ConclusionsBGL3I may take part in the complex regulating system of cellulase induction. The deletion of bgl3i offers a new strategy to improve T. reesei strain performance.

Highlights

The filamentous fungus Trichoderma reesei displays increased cellulase expression while growing on inducers such as lactose or cellulose
The disruption of the intracellular β-glucosidases CEL1A and CEL1B compromises the induction of cbh1 gene expression on lactose medium, which shows that β-glucosidases play an important role in cellulase induction by using lactose as inducer [4]
Deletion of the bgl3i gene enhances cellulase induction of T. reesei The bgl3i gene is composed of four exons and three introns, as predicted in Joint Genome Institute (JGI) (Transcript ID: TRIRE2_47268), and belongs to the GH3 family according to the Pfam database

Summary

Introduction

The filamentous fungus Trichoderma reesei (anamorph of Hypocrea jecorina) displays increased cellulase expression while growing on inducers such as lactose or cellulose. Neither d-galactose nor d-glucose, or mixtures of the two, can induce transcription of cellulase genes such as lactose. The constitutive overexpression of extracellular β-galactosidase bga abolishes the induction of cellulase expression by lactose [5,6,7]. Three major facilitator superfamily transporters were recently identified as lactose permeases and are essential for cellulase induction by lactose in T. reesei [2, 8, 9]. The disruption of the intracellular β-glucosidases CEL1A and CEL1B compromises the induction of cbh gene expression on lactose medium, which shows that β-glucosidases play an important role in cellulase induction by using lactose as inducer [4]. Except for the widely studied extracellular β-glucosidase CEL3A (BGLI) and intracellular β-glucosidases CEL1A (BGLII) and CEL1B, there are still eight other β-glucosidase genes predicted in the genome of T. reesei which have not been studied well [10]

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