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MetR is a global regulator controlling phytochrome-dependent light responses in Aspergillus nidulans

ABSTRACT: Phytochrome-dependent light signaling has been studied in several fungi. In Aspergillus nidulans light-stimulated phytochrome activates the HOG signaling pathway and thereby controls the expression of a large number of genes, many of which are related to stress responses. In a genome-wide expression analysis in A. nidulans we found that phytochrome, fphA, is under strict expression control of the central regulator of the sulfur-starvation response, MetR. This transcriptional regulator is required for the expression of genes involved in inorganic sulfur assimilation. In the presence of organic sulfur, MetR is probably ubiquitinated and possibly degraded and the transcription of sulfur-assimilation genes, e.g. sulfate permease, is turned off. The expression analysis described here revealed, however, that MetR additionally controls the expression of hundreds of genes, many of which are required for secondary metabolite production. We also show that metR mutation phenocopies fphA deletion, and five other histidine-hybrid kinases are down-regulated in the metR1 mutant. Furthermore, we show that light and phytochrome regulate the expression of at least three carbon-sulfur hydrolases. This work is a further step towards understanding the interplay between light sensing and metabolic pathways.

ORGANISM(S): Aspergillus nidulans

PROVIDER: GSE156068 | GEO | 2020/12/01

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.

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MetR is a global regulator controlling phytochrome-dependent light responses in Aspergillus nidulans

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