Molecular markers from the mitochondrial genome of arbuscular mycorrhizal fungi (Glomeromycota) : evolutionary dynamics and application

The arbuscular mycorrhizal fungi (AMF) are obligate biotrophic symbionts with a key role in ecosystem functioning by their main contribution to plant mineral nutrient uptake. A fragment of the mitochondrial large subunit gene of ribosomal RNA (mtLSU) has been established as a molecular marker for population studies in Glomus intraradices, based on its homogeneity within isolate though genetic variation among isolates.
The respective region of the mtLSU was analyzed in five species of Glomus (G. mosseae, G. geosporum, G. caledonium, G. clarum, G. coronatum) from the same major clade (Glomus group A), Glomus sp. ISCB 34 from the related Glomus group B and two species of Scutellospora. The nucleotide polymorphism was very low among related morphospecies and differences were mainly caused by the exon/intron structure, limiting the resolution to a species level. Phylogenetic analyses suggested vertical inheritance from common ancestors for some introns as well as horizontal transfer for others.
Four mitochondrial intergenic spacers (rns/nad5, atp6/nad2, nad3/nad6, and nad6/cox3) were assessed as potential intraspecific markers. Combined, they offer a resolution even higher than the mtLSU, with the highest polymorphism found in the rns/nad5 spacer, most likely caused by processes of evolutionary dynamics involving homing endonucleases.
A mtLSU PCR approach was applied to study the population structure of G. intraradices at geothermal sites in Europe and North America, revealing considerable newly-discovered mtLSU sequence types as well as previously-reported types from arable fields. The molecular survey showed strong biogeographical structure in the occurrence of G. intraradices.
Overall, this PhD thesis project showed that the genetic characteristics of the AMF mitochondrion are promising for development of molecular genetic markers and evolutionary sequence analyses, and will therefore be relevant for further studies of genetics, ecology and evolution of AMF.