Detection of a transient mitochondrial DNA heteroplasmy in the progeny of crossed genetically divergent isolates of arbuscular mycorrhizal fungi

Abstract

SummaryNonself fusion and nuclear genetic exchange have been documented in arbuscular mycorrhizal fungi (AMF), particularly in Rhizophagus irregularis. However, mitochondrial transmission accompanying nonself fusion of genetically divergent isolates remains unknown.Here, we tested the hypothesis that mitochondrial DNA (mtDNA) heteroplasmy occurs in the progeny of spores, obtained by crossing genetically divergent mtDNAs in R. irregularis isolates.Three isolates of geographically distant locations were used to investigate nonself fusions and mtDNA transmission to the progeny. We sequenced two additional mtDNAs of two R. irregularis isolates and developed isolate-specific size-variable markers in intergenic regions of these isolates and those of DAOM-197198. We achieved three crossing combinations in pre-symbiotic and symbiotic phases. Progeny spores per crossing combination were genotyped using isolate-specific markers.We found evidence that nonself recognition occurs between isolates originating from different continents both in pre-symbiotic and symbiotic phases. Genotyping patterns of individual spores from the progeny clearly showed the presence of markers of the two parental mtDNA haplotypes. Our results demonstrate that mtDNA heteroplasmy occurs in the progeny of the crossed isolates. However, this heteroplasmy appears to be a transient stage because all the live progeny spores that were able to germinate showed only one mtDNA haplotype.

Compatibility and incompatibility in hyphal anastomosis of arbuscular mycorrhizal fungi

“…In F. mosseae fusions ranged from 40 to 85 %, depending on isolates (Giovannetti et al, 2003). These results had also been confirmed by studies performed on germlings of Rhizoglomus clarus and Rhizoglomus irregulare (Croll et al, 2009;Cardenas-Flores et al, 2010;De la Providencia et al, 2013). Successive experiments increased communal knowledge of the extensive occurrence of perfect fusions in different species of tropical AMF isolates, showing that the frequency of anastomosis differed in hyphal contacts within the same or different germlings, which were 42/73 %, 33/14 %, 75/64 %, 80/91 % and 9/24 %, in isolates of Acaulospora scrobiculata, Acaulospora spinosa, Claroideoglomus etunicatum, Glomus formosanum and Rhizoglomus manihotis, respectively (Novais et al, 2013).…”

Mitochondrial Genome Rearrangements in Glomus Species Triggered by Homologous Recombination between Distinct mtDNA Haplotypes

“…The latter can involve large-scale rearrangements or insertion/loss of coding regions (Boursot et al 1987; Volz-Lingenhöhl et al 1992). In AMF, transient mitochondrial length heteroplasmy through anastomosis has recently been demonstrated for geographically distant G. irregulare in vitro isolates (de la Providencia et al 2013). The divergence in length between the two mtDNA haplotypes was caused by a variation in plasmid-related dpo insertions.…”

Genome diversity in arbuscular mycorrhizal fungi

“…The differences between isolates were largely generated by the activity of three classes of mobile element. Four further Rhizophagus mtDNAs show similar features [35][36][37].…”

“…Genome diversity in arbuscular mycorrhizal fungi Young 117 Gigaspora [4,5,9,10,11 ,15 ] Archaeosporales Ambispora Ambispora [9] Geosiphon piriformis Geosiphon piriformis [9] Paraglomerales None Set against all these reports of homoplasmy (genetic uniformity) of mtDNA in AM fungi is the observation that mitochondria (like nuclei) passed through anastomoses between distinct isolates of R. irregularis, generating spores that carried two distinct mtDNA genotypes, although this heteroplasmy was transient [36]. It remains to be determined whether AM fungi have mechanisms that purge mitochondrial diversity (or, indeed, nuclear diversity) faster than random drift alone.…”