A Protein Kinase C-Encoding Gene,<i>pkcA</i>, Is Essential to the Viability of the Filamentous Fungus<i>Aspergillus nidulans</i>

Ichinomiya, Masayuki; Uchida, Hirotaka; Koshi, Yukako; Ohta, Akio; Horiuchi, Hiroyuki

doi:10.1271/bbb.70409

Cited by 52 publications

(44 citation statements)

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“…It has been described that if an essential gene is deleted, rather than causing death, the null allele will be rescued by spontaneous generation of a heterokaryon (34). An example had been described for the filamentous fungus Aspergillus nidulans, in which the deletion of the protein kinase C-encoding gene (pkcA) was lethal and only heterokaryotic strains were obtained (18).…”

Section: Discussionmentioning

confidence: 99%

Protein Kinase A Regulatory Subunit Isoforms Regulate Growth and Differentiation in Mucor circinelloides: Essential Role of PKAR4

et al. 2012

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bThe protein kinase A (PKA) signaling pathway plays a role in regulating growth and differentiation in the dimorphic fungus Mucor circinelloides. PKA holoenzyme is comprised of two catalytic (C) and two regulatory (R) subunits. In M. circinelloides, four genes encode the PKAR1, PKAR2, PKAR3, and PKAR4 isoforms of R subunits. We have constructed null mutants and demonstrate that each isoform has a different role in growth and differentiation. The most striking finding is that pkaR4 is an essential gene, because only heterokaryons were obtained in knockout experiments. Heterokaryons with low levels of wild-type nuclei showed an impediment in the emission of the germ tube, suggesting a pivotal role of this gene in germ tube emergence. The remaining null strains showed different alterations in germ tube emergence, sporulation, and volume of the mother cell. The pkaR2 null mutant showed an accelerated germ tube emission and was the only mutant that germinated under anaerobic conditions when glycine was used as a nitrogen source, suggesting that pkaR2 participates in germ tube emergence by repressing it. From the measurement of the mRNA and protein levels of each isoform in the wild-type and knockout strains, it can be concluded that the expression of each subunit has its own mechanism of differential regulation. The PKAR1 and PKAR2 isoforms are posttranslationally modified by ubiquitylation, suggesting another regulation point in the specificity of the signal transduction. The results indicate that each R isoform has a different role in M. circinelloides physiology, controlling the dimorphism and contributing to the specificity of cyclic AMP (cAMP)-PKA pathway. Mucor circinelloides is a dimorphic fungus from the new subphylum Mucormycotina (formerly classified as Zygomycetes) that displays yeast or filamentous morphology as a consequence of different environmental conditions, including gas atmosphere and level of nutrients (33). Fungi from this subphylum are organized in multinucleated cells. M. circinelloides yeasts display multipolar budding and each cell harbors more than one nucleus, while mycelium is aseptate and has distributed nuclei along the hyphae.Fungal dimorphism is particularly important since genetic evidence indicates that in a number of pathogenic fungi in animals and plants, the morphogenetic transition is directly associated with virulence and pathogenesis (4,21,29). M. circinelloides is a causal agent of the lethal fungal infectious disease mucormycosis (6, 10), which has been reported in patients with impaired immunity (22,27,38,40,49). Recently, it has been reported that the spore size dimorphism is linked to virulence in M. circinelloides (23). The functional analysis of genes involved in the control of dimorphism in M. circinelloides is a contribution to advance the understanding of pathogenic zygomycetes.One of the key regulators of polarity in fungi, as well as of other processes such as development, mating, and virulence, is the cyclic AMP (cAMP)-dependent protein kinase A (PKA) (5, 16). The...

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Section: Discussionmentioning

confidence: 99%

Protein Kinase A Regulatory Subunit Isoforms Regulate Growth and Differentiation in Mucor circinelloides: Essential Role of PKAR4

et al. 2012

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“…Several studies suggest the involvement of protein kinase C (PkcA), but direct proof that places PkcA in line with the MAP kinase module in Aspergillus spp. is still lacking (10)(11)(12). Kwon and colleagues recently characterized five of six Rho GTPases of Aspergillus niger, and beside other functional aspects, they found that Rho2 and Rho4 are important to withstand stress caused by chitin binding agents (13).…”

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Role of the Guanine Nucleotide Exchange Factor Rom2 in Cell Wall Integrity Maintenance of Aspergillus fumigatus

et al. 2013

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Aspergillus fumigatus is a mold and the causal agent of invasive aspergillosis, a systemic disease with high lethality. Recently, we identified and functionally characterized three stress sensors implicated in the cell wall integrity (CWI) signaling of this pathogen, namely, Wsc1, Wsc3, and MidA. Here, we functionally characterize Rom2, a guanine nucleotide exchange factor with essential function for the cell wall integrity of A. fumigatus. A conditional rom2 mutant has severe growth defects under repressive conditions and incorporates all phenotypes of the three cell wall integrity sensor mutants, e.g., the echinocandin sensitivity of the ⌬wsc1 mutant and the Congo red, calcofluor white, and heat sensitivity of the ⌬midA mutant. Rom2 interacts with Rho1 and shows a similar intracellular distribution focused at the hyphal tips. Our results place Rom2 between the cell surface stress sensors Wsc1, Wsc3, MidA, and Rho1 and their downstream effector mitogen-activated protein (MAP) kinase module Bck1-Mkk2-MpkA.

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“…In A. nidulans, the Rho family GTPase RhoA was shown to be involved in establishing polarity, branching, and cell wall synthesis (13). It was suggested that the protein kinase C (PKC)-encoding gene pkcA plays an essential role in the maintenance of cell integrity and polarized growth in A. nidulans (18,41,46). The A. nidulans MpkA protein is involved in germination of conidial spores and polarized growth (4), and transcription of the mpkA gene seems to be autoregulated by the CWI pathway via MpkA (8).…”

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Putative Stress Sensors WscA and WscB Are Involved in Hypo-Osmotic and Acidic pH Stress Tolerance in Aspergillus nidulans

et al. 2011

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Wsc proteins have been identified in fungi and are believed to be stress sensors in the cell wall integrity (CWI) signaling pathway. In this study, we characterized the sensor orthologs WscA and WscB in Aspergillus nidulans. Using hemagglutinin-tagged WscA and WscB, we showed both Wsc proteins to be N-and Oglycosylated and localized in the cell wall and membrane, implying that they are potential cell surface sensors. The wscA disruptant (⌬wscA) strain was characterized by reduced colony and conidia formation and a high frequency of swollen hyphae under hypo-osmotic conditions. The deficient phenotype of the ⌬wscA strain was facilitated by acidification, but not by alkalization or antifungal agents. In contrast, osmotic stabilization restored the normal phenotype in the ⌬wscA strain. A similar inhibition was observed in the wscB disruptant strain, but to a lesser extent. In addition, a double wscA and wscB disruptant (⌬wscA ⌬wscB) strain was viable, but its growth was inhibited to a greater degree, indicating that the functions of the products of these genes are redundant. Transcription of ␣-1,3-glucan synthase genes (agsA and agsB) was significantly altered in the wscA disruptant strain, resulting in an increase in the amount of alkali-soluble cell wall glucan compared to that in the wild-type (wt) strain. An increase in mitogen-activated protein kinase (MpkA) phosphorylation was observed as a result of wsc disruption. Moreover, the transient transcriptional upregulation of the agsB gene via MpkA signaling was observed in the ⌬wscA ⌬wscB strain to the same degree as in the wt strain. These results indicate that A. nidulans Wsc proteins have a different sensing spectrum and downstream signaling pathway than those in the yeast Saccharomyces cerevisiae and that they play an important role in CWI under hypo-osmotic and acidic pH conditions.

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A Protein Kinase C-Encoding Gene,pkcA, Is Essential to the Viability of the Filamentous FungusAspergillus nidulans

Cited by 52 publications

References 46 publications

Protein Kinase A Regulatory Subunit Isoforms Regulate Growth and Differentiation in Mucor circinelloides: Essential Role of PKAR4

Protein Kinase A Regulatory Subunit Isoforms Regulate Growth and Differentiation in Mucor circinelloides: Essential Role of PKAR4

Role of the Guanine Nucleotide Exchange Factor Rom2 in Cell Wall Integrity Maintenance of Aspergillus fumigatus

Putative Stress Sensors WscA and WscB Are Involved in Hypo-Osmotic and Acidic pH Stress Tolerance in Aspergillus nidulans

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