Abstract
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 Mn(2+) concentration markedly stimulates cellulase production, total protein secretion, and the intracellular Mn(2+) concentration of Rut-C30, a cellulase hyper-producing strain of T. reesei. Furthermore, we identified two Mn(2+) 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 Mn(2+) induced a significant increase in cytosolic Ca(2+) concentration, and that this increased cytosolic Ca(2+) might be a key step in the Mn(2+)-mediated regulation of cellulase gene transcription and production. The utilization of LaCl(3) to block plasma membrane Ca(2+) channels, and deletion of crz1 (calcineurin-responsive zinc finger transcription factor 1) to interrupt calcium signaling, showed that Mn(2+) exerts the induction of cellulase genes via calcium channels and calcium signaling. To substantiate this, we identified a Ca(2+)/Mn(2+) P-type ATPase, TPMR1, which could play a pivotal role in Ca(2+)/Mn(2+) homeostasis and Mn(2+) induction of cellulase genes in T. reesei Rut-C30. CONCLUSIONS: Taken together, our results revealed for the first time that Mn(2+) stimulates cellulase production, and demonstrates that Mn(2+) upregulates cellulase genes via calcium channels and calcium signaling. Our research also provides a direction to facilitate enhanced cellulase production by T. reesei.