Aspergillus nidulans A Model for Study of Form and Asexual Reproduction

As life processes became domesticated in laboratories, a need to optimize observations led to choices of more suitable material. ... But the choices and changes of organism gradually improved our sense of the workings of living things, usually focusing on one attribute at a time.

Rowland H. Davis

Many fungi produce conidia on special hyphal branches called conidiophores. These are elaborate structures as the inflorescences of higher plants—for example, like the branching of a bunch of grapes, a spike of wheat or a capitulum of dandelion. The conidiophore is a morphological device for the rapid production in a small space of a large number of asexual (mitotically derived) reproductive spores that can be liberated and disseminated by air current, the splash of rain or insects. Conidiophores in different species are of different morphology and this is an important criterion in their identification. Because of the rapid production of large numbers of loose conidia that can be disseminated, fungi are notorious in causing epidemic in plants, spoilage of food and contamination in the laboratory unless precautions are taken.

Aspergillus nidulans (Ascomycotina) is an example of a fungus that illustrates the basic strategy of asexual reproduction. Its conidiophore is a multicellular structure comprised of a relatively small number of cell types, developing in an orderly manner and in a precisely timed sequence. Each of its conidia has a single nucleus, providing a convenient source of identical haploid cells that can be mutagenized for the production of developmental mutants. The phenotype of a colony derived from a single spore is dependent only on the genotype of the nucleus. A collection of different mutants with altered conidiophore morphology can be arranged to determine the time-line of sequence in the differentiation of a multicellular structure. Moreover, the fungus is homothallic, meaning that there is no mating type barrier for sexual reproduction; crosses can be made between any two parents. Because of these features, Timberlake and colleagues chose this fungus and developed transformation protocols, gene replacement and gene disruption techniques for understanding how a multicellular structure is formed for performing a specific function.

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