Gene targeting in filamentous fungi: the benefits of impaired repair

The extent of published fungal genome sequences call for sophisticated genetic tools to address the functions and features of annotated gene products. Gene targeting is the method of choice to assess the cellular role of a given protein, trying to replace the coding sequence by selectable markers or to fuse it to functional modules, e. g. fluorescent labels. This approach relies on homologous integration of exogenous DNA fragments, the rate of which is determined by two competing processes of double strand break repair: illegitimate and homologous recombination. Advances in targeting fungal genes have recently been achieved by suppression of the former process; for several filamentous fungi a dramatic increase in homologous integration rates is evident when this so-called non-homologous end joining pathway is inoperative, which opens the prospect of comprehensive functional studies at high throughput.