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Deciphering regulatory mechanisms associated with hemicellulose degradation in Neurospora crassa

ABSTRACT: Hemicellulose, the second most abundant plant biomass fraction after cellulose, is widely viewed as a potential feedstock for the production of liquid fuels and other value-added materials. Degradation of hemicellulose by filamentous fungi requires production of many different enzymes, which are induced by biopolymers or its derivatives and regulated mainly at the transcriptional level through transcription factors (TFs). Neurospora crassa has been shown to express and secrete plant cell wall associated enzymes. To better understand genes specifically associated with degradation of hemicellulose, we identified 353 genes by transcriptome analysis of N. crassa wild type strain grown on beechwood xylan. Exposure to xylan induces 9 of the 19 predicted hemicellulase genes. The xylanolytic phenotype of strains with deletions in genes identified from the secretome and transcriptome analysis of wild type showed that none were essential for growth on beechwood xylan. The transcription factor XlnR/Xyr1 in Aspergillus and Trichoderma species is considered to be the major transcriptional regulator of genes encoding both cellulases and hemicellulases. We identified a xlnR/xyr1 homolog in N. crassa, NCU06971, termed xlr-1 (xylanase regulator 1). Deletion of xlr-1 in N. crassa abolishes the growth on xylan and xylose, but growth on cellulose was indistinguishable from wild type. To determine regulatory mechanisms associated with hemicellulose degradation, we explored the transcriptional regulon of XLR-1 under xylose and xylanolytic versus cellulolytic conditions. XLR-1 regulated only some predicted hemicellulase genes in N. crassa and was required for a full induction of several cellulase genes. Hemicellulase gene expression was induced by a combination of release from carbon catabolite repression (CCR) and induction. However, in N. crassa, xlr-1 is subject to non-CRE-1 mediated CCR. This systematic analysis provides the similarities and differences of hemicellulose degradation and regulation mechanisms used by N. crassa in comparison to other filamentous fungi.

ORGANISM(S): Neurospora crassa

PROVIDER: GSE34098 | GEO | 2012/03/26

SECONDARY ACCESSION(S): PRJNA149903

REPOSITORIES: GEO

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Project description:Hemicellulose, the second most abundant plant biomass fraction after cellulose, is widely viewed as a potential feedstock for the production of liquid fuels and other value-added materials. Degradation of hemicellulose by filamentous fungi requires production of many different enzymes, which are induced by biopolymers or its derivatives and regulated mainly at the transcriptional level through transcription factors (TFs). Neurospora crassa has been shown to express and secrete plant cell wall associated enzymes. To better understand genes specifically associated with degradation of hemicellulose, we identified 353 genes by transcriptome analysis of N. crassa wild type strain grown on beechwood xylan. Exposure to xylan induces 9 of the 19 predicted hemicellulase genes. The xylanolytic phenotype of strains with deletions in genes identified from the secretome and transcriptome analysis of wild type showed that none were essential for growth on beechwood xylan. The transcription factor XlnR/Xyr1 in Aspergillus and Trichoderma species is considered to be the major transcriptional regulator of genes encoding both cellulases and hemicellulases. We identified a xlnR/xyr1 homolog in N. crassa, NCU06971, termed xlr-1 (xylanase regulator 1). Deletion of xlr-1 in N. crassa abolishes the growth on xylan and xylose, but growth on cellulose was indistinguishable from wild type. To determine regulatory mechanisms associated with hemicellulose degradation, we explored the transcriptional regulon of XLR-1 under xylose and xylanolytic versus cellulolytic conditions. XLR-1 regulated only some predicted hemicellulase genes in N. crassa and was required for a full induction of several cellulase genes. Hemicellulase gene expression was induced by a combination of release from carbon catabolite repression (CCR) and induction. However, in N. crassa, xlr-1 is subject to non-CRE-1 mediated CCR. This systematic analysis provides the similarities and differences of hemicellulose degradation and regulation mechanisms used by N. crassa in comparison to other filamentous fungi. Four-condition experiments (minimal medium, xylan medium,xylose and Avicel medium) of mutant strain(xlr-1) compared to wild type strain; Cy3 and Cy5 dye swap

Project description:Plant biomass holds tremendous potential as a renewable feedstock in the production of biofuels and biochemicals. The effective co-utilization of the main components cellulose and hemicellulose in plant lignocellulose is critical to the economic viability of lignocellulosic biorefineries. Here, we found that the thermophilic cellulolytic fungi Myceliophthora thermophila can utilize cellulose and hemicellulose synchronously. To investigate the underlying molecular mechanisms, we firstly checked the soluble carbohydrate of the culture using plant biomass (corncob) as sole carbon source and revealed the presence of various oligosaccharides including cellodextrin and xylodextrin, both intracellularly and extracellularly in the cultures, in addition to glucose or xylose. Based on these, intracellular oligosaccharide metabolism was proposed and confirmed by identification of cellodextrin and xylodextrin metabolism pathway. Furthermore, sugar consumption assay showed that contrasting with synchronous utilization of mixed cello-/xylo-dextrin, the inhibition effect of glucose for the metabolism of xylose and cello-/xylo-dextrin exists in this fungus, suggesting Carbon Catabolite Repression (CCR) is largely avoided at the form of oligosaccharides. Transporter MtCDT-2 showing preference to xylobiose and the tolerance of cellobiose inhibition also helps to bypass metabolic inhibition. Finally, the expression of cellulase and hemicellulase genes, were found orthogonal induction by cellobiose/Avicel and xylobiose/xylan, which conferred the ability of the strain to synchronously utilize cellulose and hemicellulose. Taken together, the orthogonal oligosaccharide catabolic pathway in this fungus establishes the molecular basis for the synchronous utilization of cellulose and hemicellulose, which sheds new light on understanding the plant biomass degradation by fungi and provides alternative paradigm for development of lignocellulose biorefinery such as consolidated bioprocessing in the future.

Project description:Filamentous fungi are powerful producers of hydrolytic enzymes for the deconstruction of plant cell wall polysaccharides. However, the central question of how these sugars are perceived in the context of the complex cell wall matrix remains largely elusive. To address this question in a systematic fashion we performed an extensive comparative systems analysis of how the model filamentous fungus Neurospora crassa responds to the three main cell wall polysaccharides: pectin, hemicellulose and cellulose. We found the pectic response to be largely independent of the cellulolytic one with some overlap to hemicellulose, and in its extent surprisingly high, suggesting advantages for the fungus beyond being a mere carbon source. Our approach furthermore allowed us to identify carbon source-specific adaptations, such as the induction of the unfolded protein response on cellulose, and a commonly induced set of 29 genes likely involved in carbon scouting. Moreover, by hierarchical clustering we generated a co-expression matrix useful for the discovery of new components involved in polysaccharide utilization. This is exemplified by the identification of lat-1, which we demonstrate to encode for the physiologically relevant arabinose transporter in Neurospora. The analyses presented here are an important step towards understanding fungal degradation processes of complex biomass. Our data are based on carbon source transfer experiments. For this, N. crassa pregrown in sucrose for 16 hrs was washed in media without carbon and then transferred to either pectin, orange peel powder (OPP), xylan, Avicel (cellulose), sucrose, or media without carbon (NoC) for another 4 hrs. Biological triplicates (pectin, Avicel, sucrose, NoC) or duplicates (OPP) were used to identify differentially expressed genes in WT. For xylan only a single library was prepared, which was found to correlate well with previously published microarray data (Sun et al. 2012; doi: 10.1128/EC.05327-11)

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Deciphering regulatory mechanisms associated with hemicellulose degradation in Neurospora crassa

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