The conservation of arbuscular mycorrhizal symbiosis between a liverwort and an angiosperm

Approximately 80% of all land plants form mutually beneficial interactions with soil fungi from the phylum Glomeromycota, a relationship called arbuscular mycorrhizal (AM) symbiosis. AM symbiosis enhances the uptake of mineral nutrients from the soil by these plants and positively affects resistance to disease and abiotic stress. AM symbiosis is predicted to have evolved in the first plants that colonized land, over 450 million years ago based on evidence from the fossil record and from the presence of AM symbiosis in the earliest diverging land plant clades. The molecular mechanisms of AM symbiosis have been elucidated in detail in the 21st century using studies in angiosperm model species, but it is not clear that these discoveries also apply to the species from other land plant clades where AM symbiosis is present. In this study, I assess the conservation of known molecular mechanisms of AM symbiosis between the model angiosperm, Medicago truncatula and the liverwort, Marchantia paleacea. Putative AM symbiosis genes were identified by phylogenetic and sequence analysis and the function of these genes in AM symbiosis was supported by expression analysis during colonization of M. paleacea with AM fungi. Functional conservation of ion channels in symbiosis signalling was demonstrated through the generation of mutants in M. paleacea by CRISPR/Cas9 genome editing, and quantification of the AM symbiosis phenotype. The conservation of molecular function was demonstrated by complementation of orthologous mutants in M. truncatula. This thesis provides insight into the evolution of the molecular mechanisms of AM symbiosis since the liverwort and angiosperm lineages diverged and provide further insights into the generation of nuclear Ca2+ oscillations during symbiosis signalling