INDUSTRIAL MYCOLOGY AND THE NEW GENETICS

The genetic investigation of fungi has been extended substantially by DNA-mediated transformation, providing a supplement to more convention al generic approaches based upon sexual and parasexual processes. Init ial transformation studies with the yeast Saccharomyces cerevisiae pro vided the model for transformation systems in other fungi with regard to methodology, vector construction and selection strategies. There ar e, however, certain differences between S. cerevisiae and filamentous fungi with regard to type of genomic insertion and the availability of shuttle vectors. Single-site linked insertions are common in yeast du e to the high level of homology required for recombination between vec tored and genomic sequences, whereas mycelial fungi often show a high frequency of heterologous and unlinked insertions, often in the form o f random and multiple-site integrations. While extrachromosomally-main tained or replicative vectors are readily available for use with yeast s, such vectors have been difficult to construct for use with filament ous fungi. The development of vectors for replicative transformation w ith these fungi awaits further study. It is proposed that replicative vectors may be inherently less efficient for use with mycelial fungi r elative to yeasts, since the mycelium, as an extended and semicontinuo us network of cells, may delimit an adequate diffusion of the vector c arrying the selectable gene, thus leading to a high frequency of abort ive or unstable transformants.