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Regulatory Mutations Affecting Sulfur Metabolism Induce Environmental Stress Response in Aspergillus nidulas

ABSTRACT: Mutations in the cysB, sconB and sconC genes affect sulfur metabolism in Aspergillus nidulans in different ways. Mutation of cysB blocks synthesis of cysteine by the main pathway leaving only the less effective alternative route. Mutations of sconB or sconC affect subunits of the SCF ubiquitin ligase complex, a negative controller of METR transcription factor, resulting in specific activation of a number of sulfur assimilation and metabolism genes, ultimately leading to elevated levels of cysteine and glutathione in scon mutants. We compared transcriptomes of these three mutants with that of a wild type strain finding that expression of a few hundred genes is altered at least twofold indicating a major reorganization of cellular metabolism. Despite the different effects of the cysB and scon mutations on sulfur metabolism they affect expression of overlapping sets of genes. We identified categories of the Functional Catalogue assigned to the differentially expressed genes and selected categories most enriched among the up- and down-regulated gene groups. Besides those involved in sulfur metabolism, many up-regulated genes are related to stress responses. The two-component signal transduction system is most enriched in genes up-regulated in the cysB, sconB and sconC mutants. This category contains histidine kinases that sense and transduce environmental signals to a cascade of protein kinases. Genes encoding heat shock proteins are also up-regulated, as are genes of the glutamate degradation pathway. The latter, also known as the GABA shunt, is induced by oxidative stress. A large group of up-regulated genes are involved in carbohydrate and energy metabolism, including genes coding for enzymes of trehalose and glycerol synthesis. Genes coding for enzymes of alcohol fermentation, which are induced in response to anaerobic stress, are also up-regulated in the mutants studied. The altered expression of the carbohydrate metabolism genes is accompanied by changes in sugar accumulation in mycelia and conidia of the mutants. Among the down-regulated genes the most numerous are those encoding membrane proteins and enzymes involved in secondary metabolism, including the penicillin biosynthesis cluster. Genes coding for lysozyme are down-regulated too. As secondary metabolites often inhibit growth of other organisms, lowered expression of genes responsible for their synthesis suggests a decreased response to biotic stress in the mutants studied.

ORGANISM(S): Aspergillus nidulans

PROVIDER: GSE54130 | GEO | 2014/02/14

SECONDARY ACCESSION(S): PRJNA235263

REPOSITORIES: GEO

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Project description:Mutations in the cysB, sconB and sconC genes affect sulfur metabolism in Aspergillus nidulans in different ways. Mutation of cysB blocks synthesis of cysteine by the main pathway leaving only the less effective alternative route. Mutations of sconB or sconC affect subunits of the SCF ubiquitin ligase complex, a negative controller of METR transcription factor, resulting in specific activation of a number of sulfur assimilation and metabolism genes, ultimately leading to elevated levels of cysteine and glutathione in scon mutants. We compared transcriptomes of these three mutants with that of a wild type strain finding that expression of a few hundred genes is altered at least twofold indicating a major reorganization of cellular metabolism. Despite the different effects of the cysB and scon mutations on sulfur metabolism they affect expression of overlapping sets of genes. We identified categories of the Functional Catalogue assigned to the differentially expressed genes and selected categories most enriched among the up- and down-regulated gene groups. Besides those involved in sulfur metabolism, many up-regulated genes are related to stress responses. The two-component signal transduction system is most enriched in genes up-regulated in the cysB, sconB and sconC mutants. This category contains histidine kinases that sense and transduce environmental signals to a cascade of protein kinases. Genes encoding heat shock proteins are also up-regulated, as are genes of the glutamate degradation pathway. The latter, also known as the GABA shunt, is induced by oxidative stress. A large group of up-regulated genes are involved in carbohydrate and energy metabolism, including genes coding for enzymes of trehalose and glycerol synthesis. Genes coding for enzymes of alcohol fermentation, which are induced in response to anaerobic stress, are also up-regulated in the mutants studied. The altered expression of the carbohydrate metabolism genes is accompanied by changes in sugar accumulation in mycelia and conidia of the mutants. Among the down-regulated genes the most numerous are those encoding membrane proteins and enzymes involved in secondary metabolism, including the penicillin biosynthesis cluster. Genes coding for lysozyme are down-regulated too. As secondary metabolites often inhibit growth of other organisms, lowered expression of genes responsible for their synthesis suggests a decreased response to biotic stress in the mutants studied. Comparison of transcriptomes of the filamentous fungus Aspergillus nidulans strains bearing mutations in the cysB, sconB or sconC genes, affecting sulfur metabolism in different ways, with that of the wild type (WT) strain. Three biological replicates of WT vs cysB and WT vs sconC comparisons were performed and four biological replicates of WT vs sconB comparison were done. Each biological replicate had two technical replicates with dye swapping. A total of twenty individual hybridizations were made.

Project description:Responses of photosynthetic organisms to sulfur starvation include (i) increasing the capacity of the cell for transporting and/or assimilating exogenous sulfate, (ii) restructuring cellular features to conserve sulfur resources, and (iii) modulating metabolic processes and rates of cell growth and division. We used microarray analyses to obtain a genome-level view of changes in mRNA abundances in the green alga Chlamydomonas reinhardtii during sulfur starvation. The work confirms and extends upon previous findings showing that sulfur deprivation elicits changes in levels of transcripts for proteins that help scavenge sulfate and economize on the use of sulfur resources. Changes in levels of transcripts encoding members of the light-harvesting polypeptide family, such as LhcSR2, suggest restructuring of the photosynthetic apparatus during sulfur deprivation. There are also significant changes in levels of transcripts encoding enzymes involved in metabolic processes (e.g., carbon metabolism), intracellular proteolysis, and the amelioration of oxidative damage; a marked and sustained increase in mRNAs for a putative vanadium chloroperoxidase and a peroxiredoxin may help prolong survival of C. reinhardtii during sulfur deprivation. Furthermore, many of the sulfur stress-regulated transcripts (encoding polypeptides associated with sulfate uptake and assimilation, oxidative stress, and photosynthetic function) are not properly regulated in the sac1 mutant of C. reinhardtii, a strain that dies much more rapidly than parental cells during sulfur deprivation. Interestingly, sulfur stress elicits dramatic changes in levels of transcripts encoding putative chloroplast-localized chaperones in the sac1 mutant but not in the parental strain. These results suggest various strategies used by photosynthetic organisms during acclimation to nutrient-limited growth. An all pairs experiment design type is where all labeled extracts are compared to every other labeled extract. Computed

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Regulatory Mutations Affecting Sulfur Metabolism Induce Environmental Stress Response in Aspergillus nidulas

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