Recombinational stability of replicating plasmids in Aspergillus nidulans during transformation, vegetative growth and sexual reproduction.

Plasmids containing the AMA1 replicon are capable of autonomous maintenance in Aspergillus nidulans. It has been reported previously that these plasmids can form concatenates by recombination in a transformed mycelium, and up to 10% of molecules are involved in such events. The present study demonstrates that plasmid recombination, although frequent during transformation, rarely occurs during vegetative growth. As a result, the structure and phenotypic stability of AMA1 plasmids generally remains unaltered for many asexual (conidial) generations. It is also evident that plasmid replication does not require specific recombination events in the AMA1 palindrome. However, during sexual reproduction, autonomous plasmids exhibit increased recombination, which results in both plasmid concatenation and integration into the chromosome.