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

Abstract

Abstract Background Trichoderma reesei Rut-C30 is a hypercellulolytic mutant strain that degrades abundant sources of lignocellulosic plant biomass into renewable biofuels. Zn2+ is an activator of enzymes in almost all organisms; however, its effect on cellulase activity has not been reported in T. reesei. Results Although high concentrations of Zn2+ severely hampered the extension of T. reesei mycelia, adding 1–4 mM Zn2+ improved cellulase production in T. reesei high-yielding cellulase-producing strain Rut-C30. The expression levels of the major cellulase genes and two critical transcription activators (xyr1 and ace3) increased significantly on Zn2+ addition. Transcriptome analysis revealed that the mRNA level of plc-e encoding phospholipase C, which is involved in the calcium signaling pathway, was enhanced by Zn2+ addition. The disruption of plc-e abolished the cellulase-positive influence of Zn2+ in the early phase, indicating that plc-e is involved in Zn2+-induced cellulase production; furthermore, supplementation with LaCl3 (a plasma membrane Ca2+ channel blocker) and deletion of crz1 (calcineurin-responsive zinc finger transcription factor 1) demonstrated that calcium signaling is partly involved in this process. Moreover, we identified the zinc-responsive transcription factor zafA; the transcriptional level of zafA decreased significantly with Zn2+ stress, and its deletion indicated that zafA mainly mediates Zn2+-induced cellulase production. Conclusions For the first time, we have demonstrated that Zn2+ was toxic to T. reesei and it remarkably promoted cellulase production. This positive influence of Zn2+ was facilitated by the gene plc-e and the transcription factor zafA. These findings provide insights into the role of Zn2+ in T. reesei and a mechanistic study of signal transduction in cellulase synthesis.