Direct and indirect gene replacements in Aspergillus nidulans

Area of Science:

• Molecular Biology
• Genetics
• Mycology

Background:

• Gene replacement is a crucial technique in molecular biology for understanding gene function.
• Previous methods for gene replacement were established in yeast (Saccharomyces cerevisiae).
• The applicability of these methods to filamentous fungi like Aspergillus nidulans was unexplored.

Purpose of the Study:

• To investigate the feasibility of DNA-mediated gene replacement in Aspergillus nidulans.
• To determine if cloned and modified DNA fragments can substitute homologous chromosomal regions.
• To adapt and evaluate gene replacement strategies developed for yeast in a fungal model.

Main Methods:

• DNA-mediated transformation using linear DNA fragments with selectable markers (trpC+, argB-).
• Construction of null alleles by inserting genes into other loci.
• Modification of genes in vitro (e.g., SpoC1 C1-C gene deletion) followed by transformation and progeny analysis.

Main Results:

• Successful replacement of the endogenous trpC- allele with a heteromorphic trpC+ allele in a minority of transformants.
• Replacement of the wild-type argB+ allele with a null argB allele in a majority of transformants (approx. 30% simultaneous trpC+).
• Demonstrated replacement of the wild-type C1-C gene copy with a modified version in progeny, with loss of plasmid DNA.

Conclusions:

• Cloned and in vitro modified DNA fragments can effectively replace homologous chromosomal DNA in Aspergillus nidulans.
• Both one-step and two-step gene replacement procedures, analogous to those in Saccharomyces cerevisiae, are viable in Aspergillus nidulans.
• This study establishes Aspergillus nidulans as a model for advanced genetic manipulation via homologous recombination.