Asexual Sporulation (asexual + sporulation)

Distribution by Scientific Domains

Selected Abstracts

Cell cycle regulator Cdc14 is expressed during sporulation but not hyphal growth in the fungus-like oomycete Phytophthora infestans

Audrey M. V. Ah Fong
Summary Cdc14 proteins are important regulators of mitosis and the cell cycle. These phosphatases have been studied previously only in yeasts and metazoans, which grow by fission or budding. Here we describe a homologue (piCdc14) from the oomycete Phytophthora infestans, a primitive eukaryote lacking a classical cell cycle. PiCdc14 complements a cdc14ts mutant of Saccharomyces cerevisiae and may function like other Cdc14 proteins, but displays a strikingly different pattern of expression. Whereas previously studied Cdc14 genes are constitutively transcribed, piCdc14 is not expressed during normal growth but instead only during asexual sporulation. In transformants of P. infestans expressing a fusion between the piCdc14 promoter and the ,-glucuronidase reporter, expression was first detected in sporangiophore initials, persisted in sporangiophores bearing immature sporangia, and later became restricted to mature sporangia. After germination, expression ended a few hours before the resumption of mitosis in hyphae emerged from the spores. Homology-dependent silencing experiments supported an essential role of piCdc14 in sporulation. It is proposed that the function of piCdc14 may be to synchronise nuclear behaviour during sporulation and maintain dormancy in spores until germination. These results help illuminate the process of sporulation in oomycetes and the evolution of the cell cycle in eukaryotes. [source]

Requirement of spermidine for developmental transitions in Aspergillus nidulans

Yuan Jin
Summary Deletion 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. [source]

Phenotypic and genetic analysis of the Triticum monococcum,Mycosphaerella graminicola interaction

Hai-Chun Jing
Summary ,,Here, the aim was to understand the cellular and genetic basis of the Triticum monococcum,Mycosphaerella graminicola interaction. ,,Testing for 5 yr under UK field conditions revealed that all 24 T. monococcum accessions exposed to a high level of natural inocula were fully resistant to M. graminicola. When the accessions were individually inoculated in the glasshouse using an attached leaf seeding assay and nine previously characterized M. graminicola isolates, fungal sporulation was observed in only three of the 216 interactions examined. Microscopic analyses revealed that M. graminicola infection was arrested at four different stages post-stomatal entry. When the inoculated leaves were detached 30 d post inoculation and incubated at 100% humidity, abundant asexual sporulation occurred within 5 d in a further 61 interactions. ,,An F2 mapping population generated from a cross between T. monococcum accession MDR002 (susceptible) and MDR043 (resistant) was inoculated with the M. graminicola isolate IPO323. Both resistance and in planta fungal growth were found to be controlled by a single genetic locus designated as TmStb1 which was linked to the microsatellite locus Xbarc174 on chromosome 7Am. ,,Exploitation of T. monococcum may provide new sources of resistance to septoria tritici blotch disease. [source]

Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation of Pyrenopeziza brassicae on leaves of oilseed rape

T. Gilles
Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen, Pyrenopeziza brassicae. Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20C, but not at 24C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12,20C, 10 h at 8C, 16 h at 6C or 24 h at 4C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20C and to 26 days as temperature decreased to 4C. At 8C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12,16C, and decreased as temperature decreased to 8C or increased to 20C. At temperatures from 8 to 20C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by ,lesions' (both log10 -transformed) at different temperatures. [source]