The Ras small GTPase RSR1 regulates cellulase production in Trichoderma reesei

Abstract

Abstract Background: Lignocellulose is known to be the most abundant renewable resource in the world and has attracted widespread attention because of its ability to produce sugars from the hydrolysis of cellulases and hemicellulases secreted by filamentous fungi. Several studies have revealed that the Ras small GTPase superfamily regulate important cellular physiological processes, including synthesis of metabolites, sporulation, cell growth, cell differentiation, and apoptosis. However, how and to what extent Ras small GTPases are participated in cellulase production remain unknown. Results: In this study, we found that the putative Ras small GTPase RSR1 repressed the expression of cellulases and xylanases. Knockout of rsr1 (∆rsr1) significantly increased cellulase production and decreased the expression levels of ACY1-cAMP-protein kinase A (PKA) signaling pathway genes and intracellular cyclic adenosine monophosphate (cAMP) levels. Loss of acy1 based on ∆rsr1 (∆rsr1∆acy1) could further increase the cellulase production and expression levels of cellulase genes, while overexpression of acy1 based on ∆rsr1 (∆rsr1-OEacy1) significantly reduced the cellulase production and transcriptional levels of cellulase genes. Our results revealed that RSR1 repressed cellulase production via ACY1-cAMP-PKA pathway. Transcriptome analysis revealed significantly increased expression of three G-protein coupled receptors (GPCRs;tre62462, tre58767, tre53238) on rsr1 knockout and approximately two-fold higher expression of ACE3 and XYR1, which transcriptionally activated cellulases. ∆rsr1∆ tre62462 exhibited a decrease in enzyme activity compared to ∆rsr1, while ∆rsr1∆tre58767 and ∆rsr1∆tre53238 showed a remarkable improvement compared to ∆rsr1. We revealed that GPCRs on the membrane sense extracellular signals and transmit them to rsr1 and then to ACY1-cAMP-PKA, thereby repressing the expression of the cellulase activators ACE3 and XYR1. These data indicated the crucial role of Ras small GTPase in regulating cellulase gene expression. Conclusions: Here, we demonstrate that some G-protein-coupled receptors and Ras small GTPases play a key role in signal transduction and cellulase gene regulation in T. reesei. Understanding the roles of these components in the regulation of cellulase gene transcription and understanding the signaling processes in T. reesei can lay the groundwork for understanding and transforming other filamentous fungi.