Genetic analysis of Aspergillus nidulans unstable transformants obtained by the biolistic process

Mitotically unstable Aspergillus nidulans argB+ transformants obtained by the biolistic process were studied in the present work. Hybridization signals from undigested DNA and pulsed-field chromosomal bands of the transformants suggested the introduced plasmid occurred as free concatenated molecules. Fifteen vigorous growth sectors released from the transformants were analysed in order to understand the mechanisms involved in their formation. All sectors showed the integration of exogenous genes into the fungal genome by homologous or heterologous recombinant events.Key words: Aspergillus nidulans, biolistic process, mitotic instability, fungal transformation.

Genetic and molecular analysis of Aspergillus nidulans transformants obtained by the biolistic process

Twenty transformants obtained by transforming the argB strain of Aspergillus nidulans by the biolistic process were analysed in detail. Eight lost the Arg+ phenotype very frequently and the other 12 were mitotically stable, even after 15 successive subculturing. To analyse the integration events, the mitotically stable transformants were submited to genetic and molecular analyses; 16.7% resulted from the integration of the transforming DNA in tandem with the chromosomal argB locus, 8.3% showed replacement of the argB mutation by wild type allele, 41.7% showed transforming DNA integrated into nonhomologous chromosomal regions at chromosome III, and 33.3% showed transforming DNA integrated into nonhomologous chromosomal regions at chromosomes others than III. Among the mitotically stable transformants, the frequency of integration into nonhomologous sites was higher by the biolistic process than that reported by the literature for protoplast-mediated transformation.Key words: Aspergillus nidulans, fungal transformation, biolistic gene transfer, gene integration, argB gene.