Autophagy is induced during cell death by incompatibility and is essential for differentiation in the filamentous fungus <i>Podospora anserina</i>

<jats:title>Summary</jats:title><jats:p>In filamentous fungi, a cell death reaction occurs when cells of unlike genotype fuse. This cell death reaction, known as incompatibility reaction, is genetically controlled by a set of loci termed <jats:italic>het</jats:italic> loci (for <jats:styled-content>het</jats:styled-content>erokaryon incompatibility loci). In <jats:italic>Podospora anserina</jats:italic>, genes induced during this cell death reaction (<jats:italic>idi</jats:italic> genes) have been identified. The <jats:italic>idi‐6/pspA</jats:italic> gene encodes a serine protease that is the orthologue of the vacuolar protease B of <jats:italic>Saccharomyces cerevisiae</jats:italic> involved in autophagy. We report here that the PSPA protease participates in the degradative autophagic pathway in <jats:italic>Podospora</jats:italic>. We have identified the <jats:italic>Podospora</jats:italic> orthologue of the <jats:italic>AUT7</jats:italic> gene of <jats:italic>S. cerevisiae</jats:italic> involved in the early steps of autophagy in yeast. This gene is induced during the development of the incompatibility reaction and was designated <jats:italic>idi‐7</jats:italic>. We have used a GFP–IDI7 fusion protein as a cytological marker of the induction of autophagy. Relocalization of this fusion protein and detection of autophagic bodies inside the vacuoles during the development of the incompatibility reaction provide cytological evidence of induction of autophagy during this cell death reaction. Therefore, cell death by incompatibility in fungi appears to be related to type II programmed cell death in metazoans. In addition, we found that <jats:italic>pspA</jats:italic> and <jats:italic>idi‐7</jats:italic> null mutations confer differentiation defects such as the absence of female reproductive structures, indicating that autophagy is required for differentiation in <jats:italic>Podospora</jats:italic>.</jats:p>