title: Self/nonself recognition in Tuber melanosporum is not mediated by a heterokaryon incompatibility system.
abstract: Vegetative incompatibility is a widespread phenomenon in filamentous ascomycetes, which limits formation of viable heterokaryons. Whether this phenomenon plays a role in maintaining the homokaryotic state of the hyphae during the vegetative growth of Tuber spp. Gene expression, polymorphism analysis as well as targeted in vitro experiments allowed us to test whether a heterokaryon incompatibility (HI) system operates in Tuber melanosporum. HI is controlled by different genetic systems, often involving HET domain genes and their partners whose interaction can trigger a cell death reaction. Putative homologues to HI-related genes previously characterized in Neurospora crassa and Podospora anserina were identified in the T. melanosporum genome. However, only two HET domain genes were found. In many other ascomycetes HET domains have been found within different genes including some members of the NWD (NACHT and WD-repeat associated domains) gene family of P. anserina. More than 50 NWD homologues were found in T. melanosporum but none of these contain a HET domain. All these T. melanosporum paralogs showed a conserved gene organization similar to the microexon genes only recently characterized in Schistosoma mansoni. Expression data of the annotated HI-like genes along with low allelic polymorphism suggest that they have cellular functions unrelated to HI. Moreover, morphological analyses did not provide evidence for HI reactions between pairs of genetically different T. melanosporum strains. Thus, the maintenance of the genetic integrity during the vegetative growth of this species likely depends on mechanisms that act before hyphal fusion.
authors.affiliation: Dipartimento di Protezione e Valorizzazione Agroalimentare, University of Bologna, Via Fanin 46, 40127 Bologna, Italy.
authors.forename: Mirco
authors.initials: M
authors.lastname: Iotti
authors.forename: Andrea
authors.initials: A
authors.lastname: Rubini
authors.forename: Emilie
authors.initials: E
authors.lastname: Tisserant
authors.forename: Annegret
authors.initials: A
authors.lastname: Kholer
authors.forename: Francesco
authors.initials: F
authors.lastname: Paolocci
authors.forename: Alessandra
authors.initials: A
authors.lastname: Zambonelli
mesh_terms: D001203:Ascomycota / Q000235:genetics* / Q000254:growth & development*; D016000:Cluster Analysis; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D020869:Gene Expression Profiling; D005800:Genes, Fungal; D025301:Hyphae / Q000235:genetics / Q000254:growth & development; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D017434:Protein Structure, Tertiary; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D004271:DNA, Fungal