*Croll, Daniel; Giovannetti, Manuela; Sbrana, Cristiana; Koch, Alexander M.;  Ehinger, Martine;  Lammers, Peter J.; Sanders,  Ian R. Non-self vegetative fusion and genetic exchange in arbuscular mycorrhizal fungi. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-17.  Click here to download the presentation on pdf format.

Arbuscular mycorrhizal fungi (AMF) form symbioses with the majority of plants, improving plant nutrition and promoting plant diversity. They form extensive underground hyphal networks simultaneously connecting the roots of different plant species. Network growth is thought to be entirely clonal and the fungi are considered to have been asexual for at least 400 million years. AMF individuals are multigenomic, containing populations of genetically different nuclei. Despite this unusual genome organization, key features of the AMF life-cycle are still unknown, preventing a full understanding of AMF genetics. In fungi non-self recognition mechanisms have evolved to prevent fusions of hyphae (anastomoses) among different individuals, and, therefore, prevent genetic exchange. To date, no empirical evidence exists for anastomosis among genetically different AMF or genetic exchange. Here we present direct evidence that genetically distinct individuals of AMF (originating from the same population) do anastomose, resulting in viable hyphal bridges through which genetic exchange could occur. Using several different molecular tools we show that genetic exchange indeed occurred between genetically different AMF. Genetic information from two parents was transmitted to the spores (progeny) and these spores were viable, forming symbioses with plant roots. Our results indicate that considerable promiscuity occurs in these fungi because anastomosis occurred in 9 out of 10 combinations of different isolates and 1 out of 9 progeny of crosses showed biparental inheritance with multiple genetic markers. The ability to experimentally perform genetic crosses among AMF lays a foundation for understanding the genetics, evolutionary biology and the ecological significance of these important plant symbionts.

Keywords: arbuscular mycorrhizal fungi, genetic exchange, anastomosis, population

*Institution: University of Lausanne

Email: daniel.croll@unil.ch