Special Interest Group Meeting

The art and design of harmony: molecular genetics of the arbuscular mycorrhizal symbiosis

Uta Paszkowski, Department of Plant Molecular Biology, The University of Lausanne, Switzerland

The mutualistic arbuscular mycorrhizal symbiosis occurs between roots of most land plants and fungi of the Glomeromycota. Mutualism is manifested in the bi-directional nutrient exchange where the plant provides photosynthates to the fungus and receives minerals, in particular phosphate, in return. Establishment of the symbiosis involves a pre-symbiotic molecular cross-talk that leads to recognition and subsequent hyphopodia formation on the root surface. The root epidermal cell underneath a hyphopodium prepares for the anticipated penetration by assembly of a prepenetration apparatus that guides the entering hypha through the cell lumen. Fungal growth continues from the outer cell layers towards the inner cortex of the root where intercellular proliferation along the longitudinal axes of the root permits rapid colonization of the root. In addition, the fungus develops highly branched hyphae, so called arbuscules, inside living cortex cells. These elaborate fungal haustoria dramatically change host cell architecture including the production of a extensive periarbuscular membrane that increases the surface area for nutrient exchange.

Over the past decade a number of plant encoded AM-factors were isolated that have provided a first glimpse into the nature and complexity of the molecular dialogue underpinning the AM symbiosis. During my presentation I will try to introduce the current understanding of this apparently harmonious interorganismic relationship.