Genetic exchange in a multigenomic fungus; Rhisophagus irregularis

Author(s): Rosikiewicz P, Sanders IR

Summary:

Rhizophagus irregularis is a model species of an arbuscular mycorrhizal fungi (AMF). The AMF forms symbiotic relationship with roots of land plants, improving plant growth and protecting plants against parasites. R. irregularis is a particularly important species of AMF because it colonizes roots of most of crop plants such as rice, potato and wheat. However, different isolates of this fungus can affect plant phenotype differently. Moreover, it recently has been shown that two isolates of AMF can exchange genetic material, a process that can alter both, plant and fungal phenotypes. R. irregularis, is a coenocytic organism, which means that many nuclei coexist and can move in the common cytoplasm. The genetic exchange between two AMF isolates occurs via vegetative hyphal fusion. However, unlike in most fungi AMF produces multinucleate spores and it has been shown that each isolate of R. irregularis carries genetically different nuclei, which are maintained in successive AMF generations. What is unknown is the fate of parental nuclei after the genetic exchange, how many parental nuclei are exchanged and whether the mix of nuclei is random. In addition the nuclei are exchange with the surrounding cytoplasm. This lead to a question whether mitochondria from both parental isolates are transmitted to the offspring and how can it influence the fungal and plant phenotypes.