Independent mitochondrial and nuclear exchanges arising in Rhizophagus irregularis crossed-isolates support the presence of a mitochondrial segregation mechanism. Issue 1 (December 2016)

• Record Type: Journal Article
• Authors: Daubois, Laurence; Beaudet, Denis; Hijri, Mohamed; de la Providencia, Ivan
• Is Part Of: BMC microbiology. Volume 16:Issue 1(2016)
• Page Start: 1
• Page End: 12
• Publication Date: 2016-12
• Subjects: Arbuscular mycorrhizal fungi -- Mitochondrial segregation -- Anastomosis -- Mitochondrial nucleoids -- Protein orthology -- Monosporal cultures; Microbiology -- Periodicals; 579.05
• DOI: 10.1186/s12866-016-0627-5
• Languages: English
• ISSNs: 1471-2180

Abstract

Abstract Background Arbuscular mycorrhizal fungi (AMF) are members of the phylum Glomeromycota, an early divergent fungal lineage that forms symbiotic associations with the large majority of land plants. These organisms are asexual obligate biotrophs, meaning that they cannot complete their life cycle in the absence of a suitable host. These fungi can exchange genetic information through hyphal fusions (i.e. anastomosis) with genetically compatible isolates belonging to the same species. The occurrence of transient mitochondrial length-heteroplasmy through anastomosis between geographically distantRhizophagus irregularis isolates was previously demonstrated in single spores resulting from crossing experiments. However, (1) the persistence of this phenomenon in monosporal culture lines from crossed parental isolates, (2) its correlation with nuclear exchanges and (3) the potential mechanisms responsible for mitochondrial inheritance are still unknown. Using the AMF model organismR. irregularis, we tested whether the presence of a heteroplasmic state in progeny spores was linked to the occurrence of nuclear exchanges and whether the previously observed heteroplasmic state persisted in monosporalin vitro crossed-culture lines. We also investigated the presence of a putative mitochondrial segregation apparatus in Glomeromycota by identifying proteins similar to those found in other fungal groups. Results We observed the occurrence of biparental inheritance both for mitochondrial and nuclear markers tested in single spores obtained from crossed-isolates. However, only one parental mitochondrial DNA and nuclear genotype were recovered in each monosporal crossed-cultures, with an overrepresentation of certain mitochondrial haplotypes. These results strongly support the presence of a nuclear-independent mitochondrial segregation mechanism inR. irregularis . Furthermore, a nearly complete set of genes was identified with putative orthology to those found in other fungi and known to be associated with the mitochondrial segregation inSaccharomyces cerevisiae and filamentous fungi. Conclusions Our findings suggest that mitochondrial segregation might take place either during spore formation or colony development and that it might be independent of the nuclear segregation machinery. We present the basic building blocks for a better understanding of the mitochondrial inheritance process and segregation in these important symbiotic fungi. The comprehension of these processes is of great importance since it has been shown that different segregated lines of the same isolate can have variable effects on the host plant.