Genetic Diversity of Isolates of Glomus mosseae from Different Geographic Areas Detected by Vegetative Compatibility Testing and Biochemical and Molecular Analysis

Abstract

We detected, for the first time, the occurrence of vegetative incompatibility between different isolates of the arbuscular mycorrhizal fungal species Glomus mosseae. Vegetative compatibility tests performed on germlings belonging to the same isolate showed that six geographically different isolates were capable of self-anastomosing, and that the percentage of hyphal contacts leading to fusions ranged from 60 to 85%. Successful anastomoses were characterized by complete fusion of hyphal walls, protoplasm continuity and occurrence of nuclei in the middle of hyphal bridges. No anastomoses could be detected between hyphae belonging to different isolates, which intersected without any reaction in 49 to 68% of contacts. Microscopic examinations detected hyphal incompatibility responses in diverse pairings, consisting of protoplasm retraction from the tips and septum formation in the approaching hyphae, even before physical contact with neighboring hyphae. Interestingly, many hyphal tips showed precontact tropism, suggesting that specific recognition signals may be involved during this stage. The intraspecific genetic diversity of G. mosseae revealed by vegetative compatibility tests was confirmed by total protein profiles and internal transcribed spacer-restriction fragment length polymorphism profiles, which evidenced a higher level of molecular diversity between the two European isolates IMA1 and BEG25 than between IMA1 and the two American isolates. Since arbuscular mycorrhizal fungi lack a tractable genetic system, vegetative compatibility tests may represent an easy assay for the detection of genetically different mycelia and an additional powerful tool for investigating the population structure and genetics of these obligate symbionts.

High genetic variability and low local diversity in a population of arbuscular mycorrhizal fungi

“…Despite the large genetic differences among isolates found within one field, the Canadian isolate was not genetically distant, and, phylogenetically, it fitted into one of the main branches of the population, which suggests either potential gene flow between the Canadian isolate and some of the Swiss population or that the total diversity comprised within a small scale may already account for most diversity on a much larger scale. This finding, however, is in contrast to the findings that geographically distant isolates do not anastomose (40).…”

“…However, to date, experimental studies have only revealed anastomoses between hyphae of spores coming from the same isolate (38,39) and not between isolates of different geographical origin (40). At the scale of our study, the spatial genetic structure of the population shows that exchange of nuclei could not have been frequent enough to cause genetic homogeneity in the population.…”

Compatibility and incompatibility in hyphal anastomosis of arbuscular mycorrhizal fungi

“…Anastomoses were observed in the same germling, where perfect fusions were formed at rates of 51-57 % in F. mosseae, 34-54 % in F. caledonius and 58-68 (Giovannetti et al, 1999). 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).…”

Histocompatibility as Adaptive Response to Discriminatory Within-Organism Conflict: A Historical Model

“…An example of such behavior is found in the ascomycete fungus Rossellinia necatrix , and it appears to be triggered by a single Mendelian factor . Although there is increasing evidence of similar behavior across fungi (Ford et al 1995;Giovannetti et al 2003;Micali and Smith 2003;Iotti et al 2012;Smith and Lafontaine 2013), there is only one example where a gene has been isolated. This example is the vic4 gene of the chestnut blight fungus Cryphonectria parasitica (Ascomycota).…”