Different transcriptional responses of haploid and diploid S. cerevisiae strains to changes in cofactor preference of XR
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Microbial Cell Factories Open Access
RESEARCH
Different transcriptional responses of haploid and diploid S. cerevisiae strains to changes in cofactor preference of XR Cai‑Yun Xie, Bai‑Xue Yang, Qing‑Ran Song, Zi‑Yuan Xia, Min Gou* and Yue‑Qin Tang*
Abstract Background: Xylitol accumulation is a major barrier for efficient ethanol production through heterologous xylose reductase-xylitol dehydrogenase (XR-XDH) pathway in recombinant Saccharomyces cerevisiae. Mutated NADH-pre‑ ferring XR is usually employed to alleviate xylitol accumulation. However, it remains unclear how mutated XR affects the metabolic network for xylose metabolism. In this study, haploid and diploid strains were employed to investi‑ gate the transcriptional responses to changes in cofactor preference of XR through RNA-seq analysis during xylose fermentation. Results: For the haploid strains, genes involved in xylose-assimilation (XYL1, XYL2, XKS1), glycolysis, and alcohol fermentation had higher transcript levels in response to mutated XR, which was consistent with the improved xylose consumption rate and ethanol yield. For the diploid strains, genes related to protein biosynthesis were upregulated while genes involved in glyoxylate shunt were downregulated in response to mutated XR, which might contribute to the improved yields of biomass and ethanol. When comparing the diploids with the haploids, genes involved in glycolysis and MAPK signaling pathway were significantly downregulated, while oxidative stress related transcription factors (TFs) were significantly upregulated, irrespective of the cofactor preference of XR. Conclusions: Our results not only revealed the differences in transcriptional responses of the diploid and haploid strains to mutated XR, but also provided underlying basis for better understanding the differences in xylose metabo‑ lism between the diploid and haploid strains. Keywords: Saccharomyces cerevisiae, Xylose fermentation, XR-XDH pathway, CRISPR/Cas9, Transcriptomics, Bioethanol Background Lignocellulosic biomass is regard as an abundant and sustainable feedstock for fuel ethanol production. Hydrolysis of lignocellulose primarily releases glucose and xylose. Saccharomyces cerevisiae as the traditional ethanol producer cannot utilize xylose. Heterologous xylose reductase-xylitol dehydrogenase (XR-XDH) pathway or xylose isomerase (XI) pathway is usually introduced *Correspondence: [email protected]; [email protected] College of Architecture and Environment, Sichuan University, No. 24, South Section 1, First Ring Road, Chengdu 610065, Sichuan, China
into S. cerevisiae to enable xylose utilization [1]. Compared with XI strains, XR-XDH strains exhibit higher xylose consumption rate and ethanol productivity [2, 3]. However, xylitol accumulates seriously due to the cofactor imbalance between NADPH-preferring XR and NAD+-dependent XDH. Numerous efforts have been made to alter the cofactor preference of XR from NADPH to NADH, however, the decreased xylitol accumulation is usually accompanied by improved or reduced xylos
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