Background: The filamentous fungus Trichoderma reesei Rut-C30 is one of the most vital fungi for the production of cellulases, which can be used for biofuel production from lignocellulose. Nevertheless, the mechanism of transmission of external stimuli and signals in modulating cellulase production in T. reesei Rut-C30 remains unclear. Calcium is a known second messenger regulating cellulase gene expression in T. reesei.
Results: In this study, we found that a biologically relevant extracellular Mn2+ concentration markedly stimulates cellulase production, total protein secretion, and the intracellular Mn2+ concentration of Rut-C30, a cellulase hyper-producing strain of T. reesei. Furthermore, we identified two Mn2+ transport proteins, designated as TPHO84-1 and TPHO84-2, indicating that they are upstream in the signaling pathway that leads to cellulase upregulation. We also found that Mn2+ induced a significant increase in cytosolic Ca2+ concentration, and that this increased cytosolic Ca2+ might be a key step in the Mn2+-mediated regulation of cellulase gene transcription and production. The utilization of LaCl3 to block plasma membrane Ca2+ channels, and deletion of crz1 (calcineurin-responsive zinc finger transcription factor 1) to interrupt calcium signaling, showed that Mn2+ exerts the induction of cellulase genes via calcium channels and calcium signaling. To substantiate this, we identified a Ca2+/Mn2+ P-type ATPase, TPMR1, which could play a pivotal role in Ca2+/Mn2+ homeostasis and Mn2+ induction of cellulase genes in T. reesei Rut-C30.
Conclusions: Taken together, our results revealed for the first time that Mn2+ stimulates cellulase production, and demonstrates that Mn2+ upregulates cellulase genes via calcium channels and calcium signaling. Our research also provides a direction to facilitate enhanced cellulase production by T. reesei.
Keywords: Calcium signaling; Cellulase; Mn2+ stimulation; Mn2+ transport; TPMR1; Trichoderma reesei.