Polyamines as Modulators of Microcycle Conidiation in Aspergillus Flavus

Khurana, Nitika; Saxena, Rajendra Kumar; Gupta, Rani; Rajam, Manchikatla Venkat

doi:10.1099/13500872-142-3-517

Cited by 29 publications

(11 citation statements)

References 25 publications

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“…Second, Δ Fvve1 conidia germinated to form short unbranched germ tubes that subsequently produced another conidium (Figs 6A and 8A). Some authors define this latter type of growth as microcycle conidiation (Maheshwari, 1991; Griffin, 1994; Khurana et al ., 1996; Cousin et al ., 2006). Third, some Δ Fvve1 conidia did not germinate to form germ tubes but instead produced a second conidium directly from the mother conidium in a manner resembling the budding growth of the yeast Saccharomyces cerevisiae (Fig.…”

Section: Resultsmentioning

confidence: 99%

FvVE1 regulates filamentous growth, the ratio of microconidia to macroconidia and cell wall formation in Fusarium verticillioides

Myung

Guse

et al. 2006

Molecular Microbiology

133

144

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SummaryThe velvet gene, veA, co-ordinates asexual and sexual development in the homothallic fungal species Aspergillus nidulans. Studies in Aspergillus parasiticus and Aspergillus fumigatus demonstrated that veA also regulates morphological differentiation in these species. Whether veA has the same role in morphogenesis in other fungal genera has not been investigated. In this work, we studied the role of the veA homologue, FvVE1, in the heterothallic fungus Fusarium verticillioides. Deletion of FvVE1 suppressed aerial hyphal growth and reduced colony surface hydrophobicity on solid media. In submerged cultures, FvVE1 deletion caused alterations in hyphal polarity, marked activation of conidiation and yeastlike growth. The latter was promoted by shaking to increase aeration of cultures. In addition, FvVE1 deletion markedly increased the ratio of macroconidia to microconidia. Supplementation of osmotic stabilizers restored the wild-type phenotype to deletion mutants, suggesting phenotypic alterations caused by FvVE1 deletion are related to cell wall defects. This is consistent with the hypersensitivity of FvVE1 deletion mutants to SDS and with the significant reduction in the mannoprotein content of mutants compared with the wild-type strain. However, no dramatic cell wall alterations were observed when mutants were examined by transmission electron microscopy. Our data strongly suggest that FvVE1 is important for cell wall integrity, cell surface hydrophobicity, hyphal polarity and conidiation pattern.

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Section: Resultsmentioning

confidence: 99%

FvVE1 regulates filamentous growth, the ratio of microconidia to macroconidia and cell wall formation in Fusarium verticillioides

Myung

Guse

et al. 2006

Molecular Microbiology

133

144

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“…The alteration in asexual to sexual spore production in the supplemented ΔspdA strain was reminiscent of Aspergillus response to sporogenic fatty acids (Champe et al ., 1987; Calvo et al ., 1999). These developmental aberrations could be a reflection of an altered spermidine to putrescine ratio as alterations in this ratio affect mycelial growth versus conidiation in A. flavus (Khurana et al ., 1996) and developmental switches in other fungi (Shapira et al ., 1989; Guevara‐Olvera et al ., 1997). Exogenous spermidine is known to reduce the rate of ornithine decarboxylase synthesis and increase the rate of ornithine decarboxylase protein degradation in many organisms including fungi (Barnett et al ., 1988; Gupta et al ., 2001).…”

Section: Discussionmentioning

confidence: 99%

Requirement of spermidine for developmental transitions in Aspergillus nidulans

Jin

Bok

Guzmán-de-Peña

et al. 2002

Molecular Microbiology

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SummaryDeletion of the spermidine synthase gene in the fungus Aspergillus nidulans results in a strain, ∆ ∆ ∆ ∆ spdA , which requires spermidine for growth and accumulates putrescine as the sole polyamine. Vegetative growth but not sporulation or sterigmatocystin production is observed when ∆ ∆ ∆ ∆ spdA is grown on media supplemented with 0.05-0.10 mM exogenous spermidine. Supplementation of ∆ ∆ ∆ ∆ spdA with ≥ ≥ ≥ ≥ 0.10 mM spermidine restores sterigmatocystin production and ≥ ≥ ≥ ≥ 0.50 mM spermidine produces a phenotype with denser asexual spore production and decreased radial hyphal growth compared with the wild type. ∆ ∆ ∆ ∆ spdA spores germinate in unsupplemented media but germ tube growth ceases after 8 h upon which time the spores swell to approximately three times their normal diameter. Hyphal growth is resumed upon addition of 1.0 mM spermidine. Suppression of a G protein signalling pathway could not force asexual sporulation and sterigmatocystin production in ∆ ∆ ∆ ∆ spdA strains grown in media lacking spermidine but could force both processes in ∆ ∆ ∆ ∆ spdA strains supplemented with 0.05 mM spermidine. These results show that increasing levels of spermidine are required for the transitions from (i) germ tube to hyphal growth and (ii) hyphal growth to tissue differentiation and secondary metabolism. Suppression of G protein signalling can over-ride the spermidine requirement for the latter but not the former transition.

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“…The sequence is reminiscent of micro-cycle sporulation, observed in prokaryote (PETRIDOU and SLEPECKY 1992). and eukaryote (LASCARIS and DEACON 1994), (Khurana et al 1996) sporulating cultures. These involve formation of new spores at the end of newly-emerged germ tubes.…”

Section: Zero Growth Ratementioning

confidence: 99%

Sporulation at minimum specific growth rate inAspergillus nidulans chemostat culture predicted using protein synthesis efficiency estimations

Bushell

Bull

1999

J. Basic Microbiol.

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Ribosomal efficiency (RE) estimates provide a quantitative descriptor of intrinsic growth rate of cell populations using readily‐obtainable experimental data. In Aspergillus nidulans chemostat cultures, RE increased linearly with growth rate over the range 25—60% of maximum growth rate (μmax), consistent with increasing ribosomal usage with increased growth rate. Above 60%, RE did not in‐crease significantly, suggesting that all ribosomes were functional at 60% of μmax, further increases in growth rate, presumably resulting from increased polypeptide chain elongation rate. Extrapolating the linear part of the RE/growth rate curve predicted zero RE at a growth rate of 0.04 h—1. Chemostat steady state cultures at 0.04 h—1 contained spores (conidia), apparently undergoing a continuous spo‐rulation/germination cycle. We propose that the RE estimates provide a means of predicting the value of minimum specific growth rate (μmin) below which net growth cannot take place.

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Polyamines as Modulators of Microcycle Conidiation in Aspergillus Flavus

Cited by 29 publications

References 25 publications

FvVE1 regulates filamentous growth, the ratio of microconidia to macroconidia and cell wall formation in Fusarium verticillioides

FvVE1 regulates filamentous growth, the ratio of microconidia to macroconidia and cell wall formation in Fusarium verticillioides

Requirement of spermidine for developmental transitions in Aspergillus nidulans

Sporulation at minimum specific growth rate inAspergillus nidulans chemostat culture predicted using protein synthesis efficiency estimations

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