Mechanism of Zn2+ regulation of cellulase production in Trichoderma reesei Rut-C30

Abstract Background Trichoderma reesei Rut-C30 is a hypercellulolytic mutant strain that degrades abundant sources of lignocellulosic plant biomass, yielding renewable biofuels. Although Zn2+ is an activator of enzymes in almost all organisms, its effects on cellulase activity in T. reesei have yet to be reported. Results Although high concentrations of Zn2+ severely suppressed the extension of T. reesei mycelia, the application of 1–4 mM Zn2+ enhanced cellulase and xylanase production in the high-yielding cellulase-producing Rut-C30 strain of T. reesei. Expression of the major cellulase, xylanase, and two essential transcription activator genes (xyr1 and ace3) increased in response to Zn2+ stimulation. Transcriptome analysis revealed that the mRNA levels of plc-e encoding phospholipase C, which is involved in the calcium signaling pathway, were enhanced by Zn2+ application. The disruption of plc-e abolished the cellulase-positive influence of Zn2+ in the early phase of induction, indicating that plc-e is involved in Zn2+-induced cellulase production. Furthermore, treatment with LaCl3 (a plasma membrane Ca2+ channel blocker) and deletion of crz1 (calcineurin-responsive zinc finger transcription factor 1) indicated that calcium signaling is partially involved in this process. Moreover, we identified the zinc-responsive transcription factor zafA, the transcriptional levels of which declined in response to Zn2+ stress. Deletion of zafA indicates that this factor plays a prominent role in mediating the Zn2+-induced excessive production of cellulase. Conclusions For the first time, we have demonstrated that Zn2+ is toxic to T. reesei, although promotes a marked increase in cellulase production. This positive influence of Zn2+ is facilitated by the plc-e gene and zafA transcription factor. These findings provide insights into the role of Zn2+ in T. reesei and the mechanisms underlying signal transduction in cellulase synthesis.