title: Maintaining two mating types: structure of the mating type locus and its role in heterokaryosis in Podospora anserina.
abstract: Pseudo-homothallism is a reproductive strategy elected by some fungi producing heterokaryotic sexual spores containing genetically different but sexually compatible nuclei. This lifestyle appears as a compromise between true homothallism (self-fertility with predominant inbreeding) and complete heterothallism (with exclusive outcrossing). However, pseudohomothallic species face the problem of maintaining heterokaryotic mycelia to fully benefit from this lifestyle, as homokaryons are self-sterile. Here, we report on the structure of chromosome 1 in mat+ and mat- isolates of strain S of the pseudohomothallic fungus Podospora anserina. Chromosome 1 contains either one of the mat+ and mat- mating types of P. anserina, which is mostly found in nature as a mat+/mat- heterokaryotic mycelium harboring sexually compatible nuclei. We identified a "mat" region ∼0.8 Mb long, devoid of meiotic recombination and containing the mating-type idiomorphs, which is a candidate to be involved in the maintenance of the heterokaryotic state, since the S mat+ and S mat- strains have different physiology that may enable hybrid-vigor-like phenomena in the heterokaryons. The mat region contains 229 coding sequences. A total of 687 polymorphisms were detected between the S mat+ and S mat- chromosomes. Importantly, the mat region is colinear between both chromosomes, which calls for an original mechanism of recombination inhibition. Microarray analyses revealed that 10% of the P. anserina genes have different transcriptional profiles in S mat+ and S mat-, in line with their different phenotypes. Finally, we show that the heterokaryotic state is faithfully maintained during mycelium growth of P. anserina, yet mat+/mat+ and mat-/mat- heterokaryons are as stable as mat+/mat- ones, evidencing a maintenance of heterokaryosis that does not rely on fitness-enhancing complementation between the S mat+ and S mat- strains.
authors.affiliation: Université Paris Diderot, Sorbonne Paris Cité, Institut des Energies de Demain, 75205 Paris Cedex 13 France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Grognet
authors.forename: Frédérique
authors.initials: F
authors.lastname: Bidard
authors.forename: Claire
authors.initials: C
authors.lastname: Kuchly
authors.forename: Laetitia Chan Ho
authors.initials: LC
authors.lastname: Tong
authors.forename: Evelyne
authors.initials: E
authors.lastname: Coppin
authors.forename: Jinane Ait
authors.initials: JA
authors.lastname: Benkhali
authors.forename: Arnaud
authors.initials: A
authors.lastname: Couloux
authors.forename: Patrick
authors.initials: P
authors.lastname: Wincker
authors.forename: Robert
authors.initials: R
authors.lastname: Debuchy
authors.forename: Philippe
authors.initials: P
authors.lastname: Silar
mesh_terms: D002467:Cell Nucleus / Q000235:genetics*; D002503:Centromere / Q000235:genetics; D015825:Chromosomes, Fungal / Q000235:genetics; D005800:Genes, Fungal / Q000235:genetics; D056084:Genetic Fitness; D056426:Genetic Loci / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D048468:Podospora / Q000166:cytology / Q000235:genetics* / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D012098:Reproduction / Q000235:genetics
chemical_list: D012333:RNA, Messenger
keywords: Podospora anserina; filamentous fungi; heterokaryosis; mat region; mating type