Abstract
BACKGROUND: Trichoderma reesei Rut-C30 is a hypercellulolytic mutant strain that degrades abundant sources of lignocellulosic plant biomass, yielding renewable biofuels. Although Zn(2+) 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 Zn(2+) severely suppressed the extension of T. reesei mycelia, the application of 1-4 mM Zn(2+) 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 Zn(2+) 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 Zn(2+) application. The disruption of plc-e abolished the cellulase-positive influence of Zn(2+) in the early phase of induction, indicating that plc-e is involved in Zn(2+)-induced cellulase production. Furthermore, treatment with LaCl(3) (a plasma membrane Ca(2+) 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 Zn(2+) stress. Deletion of zafA indicates that this factor plays a prominent role in mediating the Zn(2+)-induced excessive production of cellulase. CONCLUSIONS: For the first time, we have demonstrated that Zn(2+) is toxic to T. reesei, although promotes a marked increase in cellulase production. This positive influence of Zn(2+) is facilitated by the plc-e gene and zafA transcription factor. These findings provide insights into the role of Zn(2+) in T. reesei and the mechanisms underlying signal transduction in cellulase synthesis.