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The transcriptional activator GaaR of Aspergillus niger is required for release and utilization of d-galacturonic acid from pectin.

ABSTRACT: We identified the d-galacturonic acid (GA)-responsive transcriptional activator GaaR of the saprotrophic fungus, Aspergillus niger, which was found to be essential for growth on GA and polygalacturonic acid (PGA). Growth of the ?gaaR strain was reduced on complex pectins. Genome-wide expression analysis showed that GaaR is required for the expression of genes necessary to release GA from PGA and more complex pectins, to transport GA into the cell, and to induce the GA catabolic pathway. Residual growth of ?gaaR on complex pectins is likely due to the expression of pectinases acting on rhamnogalacturonan and subsequent metabolism of the monosaccharides other than GA.

SUBMITTER: Alazi E

PROVIDER: S-EPMC5111758 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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The transcriptional activator GaaR of Aspergillus niger is required for release and utilization of d-galacturonic acid from pectin.

Alazi Ebru E Niu Jing J Kowalczyk Joanna E JE Peng Mao M Aguilar Pontes Maria Victoria MV van Kan Jan A L JA Visser Jaap J de Vries Ronald P RP Ram Arthur F J AF

FEBS letters 20160530 12

We identified the d-galacturonic acid (GA)-responsive transcriptional activator GaaR of the saprotrophic fungus, Aspergillus niger, which was found to be essential for growth on GA and polygalacturonic acid (PGA). Growth of the ΔgaaR strain was reduced on complex pectins. Genome-wide expression analysis showed that GaaR is required for the expression of genes necessary to release GA from PGA and more complex pectins, to transport GA into the cell, and to induce the GA catabolic pathway. Residual ...[more]

PMID: 27174630

Similar Datasets

The transcriptional activator GaaR of Aspergillus niger is required for release and utilization of D-galacturonic acid from pectin

Project description:We identified the D-galacturonic acid (GA) responsive transcriptional activator GaaR of the saprotrophic fungus Aspergillus niger, which was found to be essential for growth on GA and polygalacturonic acid (PGA). Growth of the ΔgaaR strain was reduced on complex pectins. Genome-wide expression analysis showed that GaaR is required for the expression of genes necessary to release GA from PGA and more complex pectins, to transport GA into the cell and to induce the GA-catabolic pathway. Residual growth of ΔgaaR on complex pectins is likely due to expression of pectinases acting on rhamnogalacturonan and subsequent metabolism of the monosaccharides other than GA.

2017-02-10 | GSE80227 | GEO

An Evolutionarily Conserved Transcriptional Activator-Repressor Module Controls Expression of Genes for D-Galacturonic Acid Utilization in Aspergillus niger.

Project description:The expression of genes encoding extracellular polymer-degrading enzymes and the metabolic pathways required for carbon utilization in fungi are tightly controlled. The control is mediated by transcription factors that are activated by the presence of specific inducers, which are often monomers or monomeric derivatives of the polymers. A D-galacturonic acid-specific transcription factor named GaaR was recently identified and shown to be an activator for the expression of genes involved in galacturonic acid utilization in Botrytis cinerea and Aspergillus niger Using a forward genetic screen, we isolated A. niger mutants that constitutively express GaaR-controlled genes. Reasoning that mutations in the gaaR gene would lead to a constitutively activated transcription factor, the gaaR gene in 11 of the constitutive mutants was sequenced, but no mutations in gaaR were found. Full genome sequencing of five constitutive mutants revealed allelic mutations in one particular gene encoding a previously uncharacterized protein (NRRL3_08194). The protein encoded by NRRL3_08194 shows homology to the repressor of the quinate utilization pathway identified previously in Neurospora crassa (qa-1S) and Aspergillus nidulans (QutR). Deletion of NRRL3_08194 in combination with RNA-seq analysis showed that the NRRL3_08194 deletion mutant constitutively expresses genes involved in galacturonic acid utilization. Interestingly, NRRL3_08194 is located next to gaaR (NRRL3_08195) in the genome. The homology to the quinate repressor, the chromosomal clustering, and the constitutive phenotype of the isolated mutants suggest that NRRL3_08194 is likely to encode a repressor, which we name GaaX. The GaaR-GaaX module and its chromosomal organization is conserved among ascomycetes filamentous fungi, resembling the quinate utilization activator-repressor module in amino acid sequence and chromosomal organization.

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The pathway intermediate 2-keto-3-deoxy-L-galactonate mediates the induction of genes involved in D-galacturonic acid utilization in Aspergillus niger.

Project description:In Aspergillus niger, the enzymes encoded by gaaA, gaaB, and gaaC catabolize d-galacturonic acid (GA) consecutively into l-galactonate, 2-keto-3-deoxy-l-galactonate, pyruvate, and l-glyceraldehyde, while GaaD converts l-glyceraldehyde to glycerol. Deletion of gaaB or gaaC results in severely impaired growth on GA and accumulation of l-galactonate and 2-keto-3-deoxy-l-galactonate, respectively. Expression levels of GA-responsive genes are specifically elevated in the ∆gaaC mutant on GA as compared to the reference strain and other GA catabolic pathway deletion mutants. This indicates that 2-keto-3-deoxy-l-galactonate is the inducer of genes required for GA utilization.

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Carbon starvation and pectin utilization in Aspergillus nidulans

Project description:We have a cDNA microarray to investigate changes in gene expression following transfer of fungal cultures from growth on glucose to growth on pectin or no carbon source. Our goal was to asses the roles of release from carbon catabolite repression and specific induction on proteins needed for metabolism (or utilization) of a single class of complex polysaccharide. Keywords = Aspergillus Keywords = Pectin Keywords = central metabolism Keywords = pectin Keywords = carbon catabolite repression Keywords = polysaccharide Keywords = exopolygalacturonase Keywords: time-course

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The transcriptional activator XlnR regulates both xylanolytic and endoglucanase gene expression in Aspergillus niger.

Project description:The expression of genes encoding enzymes involved in xylan degradation and two endoglucanases involved in cellulose degradation was studied at the mRNA level in the filamentous fungus Aspergillus niger. A strain with a loss-of-function mutation in the xlnR gene encoding the transcriptional activator XlnR and a strain with multiple copies of this gene were investigated in order to define which genes are controlled by XlnR. The data presented in this paper show that the transcriptional activator XlnR regulates the transcription of the xlnB, xlnC, and xlnD genes encoding the main xylanolytic enzymes (endoxylanases B and C and beta-xylosidase, respectively). Also, the transcription of the genes encoding the accessory enzymes involved in xylan degradation, including alpha-glucuronidase A, acetylxylan esterase A, arabinoxylan arabinofuranohydrolase A, and feruloyl esterase A, was found to be controlled by XlnR. In addition, XlnR also activates transcription of two endoglucanase-encoding genes, eglA and eglB, indicating that transcriptional regulation by XlnR goes beyond the genes encoding xylanolytic enzymes and includes regulation of two endoglucanase-encoding genes.

| S-EPMC106473 | biostudies-literature

Inducer-independent production of pectinases in Aspergillus niger by overexpression of the D-galacturonic acid-responsive transcription factor gaaR.

Project description:The transcription factor GaaR is needed for the expression of genes required for pectin degradation and transport and catabolism of the main degradation product, D-galacturonic acid (GA) in Aspergillus niger. In this study, we used the strong constitutive gpdA promoter of Aspergillus nidulans to overexpress gaaR in A. niger. Overexpression of gaaR resulted in an increased transcription of the genes encoding pectinases, (putative) GA transporters, and catabolic pathway enzymes even under non-inducing conditions, i.e., in the absence of GA. Exoproteome analysis of a strain overexpressing gaaR showed that this strain secretes highly elevated levels of pectinases when grown in fructose. The genes encoding exo-polygalacturonases were found to be subjected to CreA-mediated carbon catabolite repression, even in the presence of fructose. Deletion of creA in the strain overexpressing gaaR resulted in a further increase in pectinase production in fructose. We showed that GaaR localizes mainly in the nucleus regardless of the presence of an inducer, and that overexpression of gaaR leads to an increased concentration of GaaR in the nucleus.

| S-EPMC5847190 | biostudies-literature

W361R mutation in GaaR, the regulator of D-galacturonic acid-responsive genes, leads to constitutive production of pectinases in Aspergillus niger.

Project description:Polysaccharides present in plant biomass, such as pectin, are the main carbon source for filamentous fungi. Aspergillus niger naturally secretes pectinases to degrade pectin and utilize the released monomers, mainly D-galacturonic acid. The transcriptional activator GaaR, the repressor of D-galacturonic acid utilization GaaX, and the physiological inducer 2-keto-3-deoxy-L-galactonate play important roles in the transcriptional regulation of D-galacturonic acid-responsive genes, which include the genes encoding pectinases. In this study, we described the mutations found in gaaX and gaaR that enabled constitutive (i.e., inducer-independent) expression of pectinases by A. niger. Using promoter-reporter strains (PpgaX-amdS) and polygalacturonic acid plate assays, we showed that W361R mutation in GaaR results in constitutive production of pectinases. Analysis of subcellular localization of C-terminally eGFP-tagged GaaR/GaaRW 361R revealed important differences in nuclear accumulation of N- versus C-terminally eGFP-tagged GaaR.

| S-EPMC6528562 | biostudies-literature

Carbon starvation and pectin utilization in Aspergillus nidulans

2010-06-11 | E-GEOD-2417 | biostudies-arrayexpress

Combinatorial control of gene expression in Aspergillus niger grown on sugar beet pectin.

Project description:Aspergillus niger produces an arsenal of extracellular enzymes that allow synergistic degradation of plant biomass found in its environment. Pectin is a heteropolymer abundantly present in the primary cell wall of plants. The complex structure of pectin requires multiple enzymes to act together. Production of pectinolytic enzymes in A. niger is highly regulated, which allows flexible and efficient capture of nutrients. So far, three transcriptional activators have been linked to regulation of pectin degradation in A. niger. The L-rhamnose-responsive regulator RhaR controls the production of enzymes that degrade rhamnogalacturonan-I. The L-arabinose-responsive regulator AraR controls the production of enzymes that decompose the arabinan and arabinogalactan side chains of rhamnogalacturonan-II. The D-galacturonic acid-responsive regulator GaaR controls the production of enzymes that act on the polygalacturonic acid backbone of pectin. This project aims to better understand how RhaR, AraR and GaaR co-regulate pectin degradation. For that reason, we constructed single, double and triple disruptant strains of these regulators and analyzed their growth phenotype and pectinolytic gene expression in A. niger grown on sugar beet pectin.

| S-EPMC5617896 | biostudies-literature

Identification of amino acid residues critical for catalysis and stability in Aspergillus niger family 1 pectin lyase A.

Project description:Site-directed-mutagenesis studies were performed on family 1 pectin lyase A (PL1A) from Aspergillus niger to gain insight into the reaction mechanism for the pectin lyase-catalysed beta-elimination cleavage of methylesterified polygalacturonic acid and to stabilize the enzyme at slightly basic pH. On the basis of the three-dimensional structures of PL1A [Mayans, Scott, Connerton, Gravesen, Benen, Visser, Pickersgill and Jenkins (1997) Structure 5, 677-689] and the modelled enzyme-substrate complex of PL1B [Herron, Benen, Scavetta, Visser and Jurnak (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 8762-8769], Asp154, Arg176, Arg236 and Lys239 were mutagenized. Substituting Arg236 with alanine or lysine rendered the enzyme completely inactive, and mutagenesis of Arg176 and Lys239 severely affected catalysis. The Asp154-->Arg and Asp154-->Glu mutant enzymes were only moderately impaired in respect of catalysis. The results strongly indicate that Arg236, which is sandwiched between Arg176 and Lys239, would initiate the reaction upon enzyme-substrate interaction, through the abstraction of the proton at C5 of the galacturonopyranose ring. The positively charged residues Arg176 and Lys239 are responsible for lowering the p K a of Arg236. Arg176 and Lys239 are maintained in a charged state by interacting with Asp154 or bulk solvent respectively. The deprotonation of the Asp186-Asp221 pair was proposed to be responsible for a pH-driven conformational change of PL1A [Mayans, Scott, Connerton, Gravesen, Benen, Visser, Pickersgill and Jenkins (1997) Structure 5, 677-689]. Substitution of Asp186 and Asp221 by Asn186 and Asn221 was expected to stabilize the enzyme. However, the Asp186-->Asn/Asp221-->Asn enzyme appeared less stable than the wild-type enzyme, even at pH 6.0, as evidenced by fluorescence studies. This demonstrates that the pH-dependent conformational change is not driven by deprotonation of the Asp186-Asp221 pair.

| S-EPMC1223150 | biostudies-other

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