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Genetic bypass of Aspergillus nidulans crzA function in calcium homeostasis.

ABSTRACT: After dephosphorylation by the phosphatase calcineurin, the fungal transcription factor CrzA enters the nucleus and activates the transcription of genes responsible for calcium homeostasis and many other calcium-regulated activities. A lack of CrzA confers calcium-sensitivity to the filamentous fungus Aspergillus nidulans. To further understand calcium signaling in filamentous fungi and to identify genes that interact genetically with CrzA, we selected for mutations that were able to suppress crzA? calcium intolerance and identified three genes. Through genetic mapping, gene sequencing, and mutant rescue, we were able to identify these as cnaB (encoding the calcineurin regulatory subunit), folA (encoding an enzyme involved in folic acid biosynthesis, dihydroneopterin aldolase), and scrC (suppression of crzA(-), encoding a hypothetical protein). By using a calcium indicator, Fluo-3, we were able to determine that the wild-type and the suppressor strains were either able to regulate intracellular calcium levels or were able to take up and or store calcium correctly. The increased expression of calcium transporters, pmcA and/or pmcB, in suppressor mutants possibly enabled tolerance to high levels of calcium. Our results suggest that a cnaB suppressor mutation confers calcium tolerance to crzA? strains through restoration of calcium homeostasis. These results stress that in A. nidulans there are calcineurin-dependent and CrzA-independent pathways. In addition, it is possible that CrzA is able to contribute to the modulation of folic acid biosynthesis.

SUBMITTER: Almeida RS

PROVIDER: S-EPMC3704241 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature

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Genetic bypass of Aspergillus nidulans crzA function in calcium homeostasis.

Almeida Ricardo S RS Loss Omar O Colabardini Ana Cristina AC Brown Neil Andrew NA Bignell Elaine E Savoldi Marcela M Pantano Sergio S Goldman Maria Helena S MH Arst Herbert N HN Goldman Gustavo H GH

G3 (Bethesda, Md.) 20130708 7

After dephosphorylation by the phosphatase calcineurin, the fungal transcription factor CrzA enters the nucleus and activates the transcription of genes responsible for calcium homeostasis and many other calcium-regulated activities. A lack of CrzA confers calcium-sensitivity to the filamentous fungus Aspergillus nidulans. To further understand calcium signaling in filamentous fungi and to identify genes that interact genetically with CrzA, we selected for mutations that were able to suppress cr ...[more]

PMID: 23665873

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Project description:Microarray analysis was used to identify the calcium-responsive genes dependent on CrzA in the filamentous fungus Aspergillus nidulans. In order to identify such genes, we conducted the two types of experiment. One was a comparison between wild type with calcium treatment and wild type without calcium treatment. Another was a comparison between wild type with calcium treatment and crzA mutant with calcium treatment. From a comparison between the results of these experiments, we could identify the genes whose expression was induced or repressed in response to calcium in a manner dependent on CrzA. KEY WORD; Aspergillus nidulans, calcium response, crzA Conidia of wild type or crzA mutant strains were incubated at 37C in CD medium for 18h and treated with or without calcium (final concentration; 50 mM) for 15 min. The mycelia were harvested and frozen in liquid nitrogen, ground to a powder, and used for RNA preparation. mRNA was purified and used for hybridization experiments. A total of 2 hybridizations were performed for each microarray experiment described in the summary. The following replicates were carried out: 1. In-slide replicates were carried out for each analyses. 2. Dye swap replicates were carried out for each analyses. The slides were scanned with an Axon GenePix 4000B scanner (Molecular Devices). The resulting TIFF images were imported into GenePix Pro and fluorescent intensity of spots were calculated for each of the Cy3 and Cy5 channels. Global normalization was applied to all analyses. Following normalization, spots whose Cy3 or Cy5 intensity was less than 0 were removed from the data set (the exceptional case was that intensity of the other channel was more than 100). The dye-swap replicates and in-slide replicates were subjected to all analyses. Finally, gene expression ratios (channel 2/channel 1) were calculated for each replicates. Gene expression was considered to be significantly higher or lower whenever the spot intensity changed by at least 2-fold in all four replicates.

Project description:The eukaryotic calcium/calmodulin-dependent protein phosphatase calcineurin is crucial for the environmental adaption of fungi. However, the mechanism of coordinate regulation of the response to salt stress by calcineurin and the high-affinity calcium channel CchA in fungi is not well understood. Here we show that the deletion of cchA suppresses the hyphal growth defects caused by the loss of calcineurin under salt stress in Aspergillus nidulans Additionally, the hypersensitivity of the ?cnaA strain to extracellular calcium and cell-wall-damaging agents can be suppressed by cchA deletion. Using the calcium-sensitive photoprotein aequorin to monitor the cytoplasmic Ca(2+) concentration ([Ca(2+)]c) in living cells, we found that calcineurin negatively regulates CchA on calcium uptake in response to external calcium in normally cultured cells. However, in salt-stress-pretreated cells, loss of either cnaA or cchA significantly decreased the [Ca(2+)]c, but a deficiency in both cnaA and cchA switches the [Ca(2+)]c to the reference strain level, indicating that calcineurin and CchA synergistically coordinate calcium influx under salt stress. Moreover, real-time PCR results showed that the dysfunction of cchA in the ?cnaA strain dramatically restored the expression of enaA (a major determinant for sodium detoxification), which was abolished in the ?cnaA strain under salt stress. These results suggest that double deficiencies of cnaA and cchA could bypass the requirement of calcineurin to induce enaA expression under salt stress. Finally, YvcA, a member of the transient receptor potential channel (TRPC) protein family of vacuolar Ca(2+) channels, was proven to compensate for calcineurin-CchA in fungal salt stress adaption.IMPORTANCE The feedback inhibition relationship between calcineurin and the calcium channel Cch1/Mid1 has been well recognized from yeast. Interestingly, our previous study (S. Wang et al., PLoS One 7:e46564, 2012, http://dx.doi.org/10.1371/journal.pone.0046564) showed that the deletion of cchA could suppress the hyphal growth defects caused by the loss of calcineurin under salt stress in Aspergillus nidulans In this study, our findings suggest that fungi are able to develop a unique mechanism for adapting to environmental salt stress. Compared to cells cultured normally, the NaCl-pretreated cells had a remarkable increase in transient [Ca(2+)]c Furthermore, we show that calcineurin and CchA are required to modulate cellular calcium levels and synergistically coordinate calcium influx under salt stress. Finally, YvcA, a member of of the TRPC family of vacuolar Ca(2+) channels, was proven to compensate for calcineurin-CchA in fungal salt stress adaption. The findings in this study provide insights into the complex regulatory links between calcineurin and CchA to maintain cytoplasmic Ca(2+) homeostasis in response to different environments.

Dataset Information

Genetic bypass of Aspergillus nidulans crzA function in calcium homeostasis.

Publications

Genetic bypass of Aspergillus nidulans crzA function in calcium homeostasis.

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