Submitted to: Journal of Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2018
Publication Date: 4/23/2018
Citation: Liu, Z.L., Wang, X., Weber, S.A. 2018. Tolerant industrial yeast Saccharomyces cerevisiae posses a more robust cell wall integrity signaling pathway against 2-furaldehyde and 5-(hydroxymethyl)-2-furaldehyde. Journal of Biotechnology. 276-277:15-24. doi: 10.1016/j.jbiotec.2018.04.002.
DOI: https://doi.org/10.1016/j.jbiotec.2018.04.002

Interpretive Summary: Cell wall integrity signaling pathway in fungi detects harmful environmental stimuli and transmits the signal for the yeast to fortify and repair damages to the cell against the stress conditions. Development of more robust yeast strains is needed toward a sustainable lignocellulose-to-biofuels production, however, little is known about the cell wall integrity pathway for the industrial yeast. This research investigated comparative gene expression dynamics using pathway-based qRT-PCR (quantitative real time polymerase chain reaction) array assays for a tolerant industrial yeast strain developed at ARS (Saccharomyces cerevisiae NRRL Y-50049) and a laboratory strain (BY4741). This research found that all cell wall integrity pathway genes in Y-50049 were more resistant and all five sensor genes shared the same signaling function against 2-furaldehyde (furfural) and 5-[hydroxymethyl]-2-furaldehyde (HMF), representative inhibitors associated with biofuels conversion. Sensor gene WSC3 displayed significantly higher levels of increased expression throughout the entire time-course study in response to challenges of furfural and HMF, which suggested WSC3 as a key sensor gene with the special capability to detect and transmit the signal against furfural and HMF to maintain cell response and function. Three amino acid mutations found in the encoding WSC3 gene may contribute to the specific function of the sensor gene. Results of this research add a new dimension to understand mechanisms of the yeast tolerance. New knowledge obtained from this study aids continued efforts in development of the next-generation biocatalyst for low-cost and sustainable biofuels production from lignocellulose materials.

Technical Abstract: Cell wall integrity signaling pathway in Saccharomyces cerevisiae is a conserved function for detecting and responding to cell stress conditions but less understood for industrial yeast. We dissected gene expression dynamics for a tolerant industrial yeast strain NRRL Y-50049 in response to challenges of furfural and HMF through comparative quantitative gene expression analysis using pathway-based qRT-PCR array assays. All tested genes from Y-50049, except for MLP2, demonstrated more resistant and highly elevated gene expression levels than that from a laboratory strain BY4741. While all five sensor encoding genes WSC1, WSC2, WSC3, MID2 and MTL1 from both strains were activated in response to the furfural-HMF treatment, WSC3 from Y-50049 displayed the most significantly increased expression over time than that from BY4741 and any other sensor genes from Y-50049. These results suggested all the five sensor genes shared the same signaling function against furfural and HMF, but gene WSC3 poses the special capability, as a key sensor gene, to dominate the signal transmission and maintain the robust CWI of the industrial yeast. Among five single nucleotide variations discovered in WSC3 from Y-50049, three were found to be non-synonymous mutations resulting in amino acid alterations of Ser158->Tyr158, Val186->Ile186, and Glu430->Asp430. Such mutations of WSC3 in Y-50049 may contribute to its special signaling capability in response to furfural-HMF. The more robust cell wall integrity signaling pathway of NRRL Y-50049 discovered in this study adds a new dimension to understand the mechanisms of the yeast tolerance and aid the development of the next-generation biocatalyst.