Neurospora crassa, bread mold

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Taxonomic lineage

cellular organisms - Eukaryota - Fungi/Metazoa group - Fungi - Dikarya - Ascomycota - Pezizomycotina - Sordariomycetes - Sordariomycetidae - Sordariales - Sordariaceae - Neurospora - Neurospora crassa

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Brief facts

• Neurospora crassa is a filamentous fungus, a bread mold, which in its natural environments can be found growing on dead plant matters predominantly in tropical and subtropical regions.
• Neurospora crassa is one of most important model organisms of our times. Most of its life stages are haploid which significantly simplifies genetic analysis. Research programs dedicated to Neurospora crassa focus on circadian rhythms, genetiss, gene silencing, ecology, evolution, and many other areas.

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Life cycle

Life Cycle Stages

• Asexual A haploid asexual spore (micro- or macroconidium) germinates and grows turning into multinuleated branched thread (hypha); a mass of hyphae constitutes a mycelium of the fungus colony; a colony buds off more conidia from aerial hyphae, and these disperse and repeat the asexual cycle.
• Sexual In the heterothalic species N. crassa, colonies of opposite mating type, A and a, must interact to give the series of events resulting in fruiting body formation, meiosis, and the generation of dormant ascospores; only a single copy of a mating type sequence is present ina haploid genome; two strains of opposite mating type cannot form a stable heterokaryon during vegetative growth; instead, they fuse abortively to give a heterokaryon incompatibility reaction, which results in death of the cells along the fusion line.
• Vegetative growth This is phase of growth of hyphae to form a mycelium not bearing fruiting bodies.

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Tissues

Fungal Components

• Conidium A vegetative spore; two types of conidial differentiation involve distinct developmental pathways, independent of each other.
  • Microconidium A uninucleate conidium; The microconidia can function either as spermatia (male gametes) or as asexual reproductive structures or both; in nature they probably function exclusively in fertilization of protoperithecia; unlike microconidia of some related ascomycetes, those of Neurospora are capable of germination, providing viable uninucleate haploid cells which are desired in several types of investigations.
  • Macroconidium A multinucleate conidium (blastoconidium and arthroconidium); macroconidia are produced in very large numbers and serve for asexual reproduction and distribution of the fungus; production of macroconidia happens once in ~24 hours (circadian rhythm) on aerial hyphae; namely these brightly pigmented structures were first recognized in 1843 on mouldy bread in bakeries of Paris; why does Neurospora employ a circadian mechanism for the formation of macroconidia that do not directly function in dissemination and survival? (ref. Maheshwari R., J Biosci. 2007).
• Mycelium MeSH A mass of branching, threadlike hyphae; mycelium can be in sexual state (bearing fruiting bodies) and in asexual state (growing biomass and producing conidia).
  • Hypha MeSH Threadlike filaments forming the mycelium of a fungus.
    • Aerial hypha Hypha that raises above substrate and produces conidia.
• Perithecium A fruiting body; a structure where nuclei of different mating types fuse resulting in transient diploid nuclei which undergo meiosis.
  • Ascospore Four haploid products of one meiosis undergoes a further mitotic division, resulting in an octad of eight ascospores enclosed in a sac called ascus.

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Mating types

The equivalent of the sex in lower organisms. The two mating types of Neurospora are determined by completely different DNA sequences at single chromosomal locus.

• Mating type A A strain of N. crassa that carries DNA sequence MAT A.
• Mating type a A strain of N. crassa that carries DNA sequence MAT a.

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References

• Dong W, Tang X, Yu Y, Nilsen R, Kim R, Griffith J, Arnold J, Schüttler HB. Systems biology of the clock in Neurospora crassa. PLoS One. 2008 Aug 29;3(8):e3105.

  

  The clock of N. crassa is remarkably adaptive in its entrainment to varied artificial days. Replicate race tubes are inoculated at one end and subject to a 6 hr, 18 hr, and 48 hr artificial day over 7 ordinary days. The clock is manifested by the appearance of orange bands (i.e., asexual production of spores) as the culture grows to the other end of the tube.
  In each artificial day the race tubes experienced:
  (A) 3 hrs light and 3 hrs dark,
  (B) 9 hrs light and 9 hrs dark, or
  (C) 24 hrs light and 24 hrs dark. It can be seen that the number of conidial bands tracked the number of artificial days experienced.

• Maheshwari R. Circadian rhythm in the pink-orange bread mould Neurospora crassa: for what? J Biosci. 2007 Sep;32(6):1053-8.
• Borkovich KA et al. Lessons from the genome sequence of Neurospora crassa: tracing the path from genomic blueprint to multicellular organism. Microbiol Mol Biol Rev. 2004 Mar;68(1):1-108.
• Maheshwari R. Microconidia of Neurospora crassa. Fungal Genet Biol. 1999 Feb;26(1):1-18.
• Coppin E et al. Mating types and sexual development in filamentous ascomycetes. Microbio Mol Biol Rev. 1997 Dec;61(4):411-28.
• Metzenberg RL, Glass NL. Mating type and mating strategies in Neurospora. Bioessays. 1990 Feb;12(2):53-9.
• PubMed free full-text articles: major topic "Neurospora"

Websites

• The Neurospora Home Page
• Wikipedia: Neurospora crassa

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