Most flowering plants have the capacity to engage in endosymbioses with fungi from the Glomeromycotina, more commonly known as arbuscular mycorrhizal (AM) fungi. These mutualistic associations develop in the roots where the fungi are accommodated in newly-generated membrane-bound compartments in the inner cortical cells. Here, the plant supplies carbon to fungus and receives mineral nutrients which the fungus accesses from the surrounding soil. Thus, the symbiosis has a positive impact on plant health, particularly during growth in low phosphorus environments. Development of AM symbiosis is complex and involves the coordinate differentiation of both symbionts to generate the endosymbiotic interfaces that enable nutrient exchange. An overarching goal of our research is to gain a mechanistic understanding of development and functioning of the symbiosis. To this end, we are currently focusing on a set of plant genes (~70 ortholog groups) that are present exclusively in AM symbiosis host plants. Many of these are essential for AM symbiosis and underlie the cellular and metabolic adaptations for endosymbiont accommodation, nutrient provisioning and nutrient transfer. While AM conserved genes are important, they comprise only a small subset of the plant’s genetic program for symbiosis and RNA-seq datasets reveal several hundred differentially expressed genes in mycorrhizal roots. To extend and further resolve the mycorrhizal root transcriptome we are using single cell and spatial transcriptomics. These approaches are bringing cellular resolution to the plant transcriptome and shedding new light on the AM fungal transcriptome. Progress in these areas will be discussed.
