Cyclic AMP-dependent protein kinase is involved in morphogenesis of Aspergillus niger a aThe EMBL accession number for the sequence reported in this paper is AJ296317.

Abstract

The cAMP signal transduction pathway controls many processes in fungi. The pkaR gene, encoding the regulatory subunit (PKA-R) of cAMP-dependent protein kinase (PKA), was cloned from the industrially important filamentous fungus Aspergillus niger. To investigate the involvement of PKA in morphology of A. niger, a set of transformants which overexpressed pkaR or pkaC (encoding the catalytic subunit of PKA) either individually or simultaneously was prepared as well as mutants in which pkaR and/or pkaC were disrupted. Strains overexpressing pkaR or both pkaC and pkaR could not be distinguished from the wild-type, suggesting that regulation of PKA activity is normal in these strains. Absence of PKA activity resulted in a two- to threefold reduction in colony diameter on plates. The most severe phenotype was observed in the absence of PKA-R, i.e., very small colonies on plates, absence of sporulation and complete loss of growth polarity during submerged growth. Suppressor mutations easily developed in the DeltapkaR mutant and one of these mutants appeared to lack PKA-C activity. These data suggest that cAMP-dependent protein phosphorylation in A. niger regulates growth polarity and formation of conidiospores.

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

“…However, the different mutants are different from the wt in both microscopic and macroscopic phenotypic features. A characteristic that seems to be a common feature of R mutants of filamentous fungi is a slower radial growth, since besides our own results, this has also been reported for N. crassa, C. lagenarium, A. fumigatus, and A. niger (2,46,51,54). Germination rates of the fungal R mutant strains are lower than those of the wt strains.…”

“…Germination rates of the fungal R mutant strains are lower than those of the wt strains. Sporulation or conidiation defects also appear to be common to these mutants in filamentous fungi, such as A. niger, A. fumigatus, or C. lagenarium (46,51,54). Some R subunit mutants also show a loss of growth polarity, as in A. niger, C. albicans, and N. crassa (2,8,46).…”

“…Thus, zygomycetes seem to be the only class of fungi that have more than one isoform for the R subunit (1,2,8,9,11,14,26,46,50,51,52,54). The corresponding mutants with mutations in the genes encoding the PKA regulatory subunit have been obtained from several of these fungi, and there does not seem to be a unique way in how fungi respond to the deletion of the R subunit, since some of them, such as A. niger (46), have the same level of PKA activity as in the wild-type cell, whereas in others, such as C. neoformans or A. fumigatus (11,54), the PKA activity is increased. However, the different mutants are different from the wt in both microscopic and macroscopic phenotypic features.…”

Protein kinase A is involved in the control of morphology and branching during aerobic growth of Mucor circinelloides

“…The role of PKA in the control of morphology and hyphal branching has been shown recently for Aspergillus niger (Saudohar et al, 2002) using genetic approaches. While a null mutation in the A. niger pkaR gene led to a small colony phenotype and lack of conidiation, an increase in pkaR expression did not result in any measurable phenotypic difference (Saudohar et al, 2002).…”

“…While a null mutation in the A. niger pkaR gene led to a small colony phenotype and lack of conidiation, an increase in pkaR expression did not result in any measurable phenotypic difference (Saudohar et al, 2002). The pkaR and pkaC genes of M. circinelloides have been cloned recently.…”