ami1, an orthologue of the Aspergillus nidulans apsA gene, is involved in nuclear migration events throughout the life cycle of Podospora anserina

The Podospora anserina amil-1 mutant was identified as a male-sterile su ai n. Microconidia (which act as male gametes) form, but are anucleate. Paraph ysae from the perithecium beaks are also anucleate when amil-1 is used as t he female partner in a cross. Furthermore, in crosses heterozygous for amil -1, some crozier cells are uninucleate rather than binucleate. In addition to these nuclear migration defects, which occur at the transition between s yncytial and cellular states, amil-1 causes abnormal distribution of the nu clei in both mycelial filaments and asci. Finally, an amil-1 strain bearing information for both mating types is unable to self-fertilize. The ami1 ge ne is an orthologue of the Aspergillus nidulans apsA gene, which controls n uclear positioning in filaments and during conidiogenesis (at the syncytial /cellular transition). The ApsA and AMI1 proteins display 42% identity and share structural features. The apsA gene complements some amil-1 defects: i t increases the percentage of nucleate microconidia and restores self-ferti lity in an amil-1 mat+ (mat-) strain. The latter effect is puzzling, since in apsA null mutants sexual reproduction is quite normal. The functional di fferences between the two genes are discussed with respect to their possibl e history in these two fungi, which are very distant in terms of evolution.