Molecular Mechanisms Governing Arbuscular Mycorrhiza Development and Function

The Arbuscular Mycorrhiza (AM), the root endosymbiosis between the vast majority of land plants and AM fungi, is established in a series of developmental steps; a pre-symbiotic phase of signal exchange, the intracellular penetration of the hyphae through the root's outer cell layers, the hyphal colonization of the root cortex and finally the formation of arbuscules. The obligate biotrophic AM fungi deliver phosphate and nitrogen compounds to the plant root and in turn receive carbon sources mainly in the form of hexoses. Genetic analyses of nodulating plant species impaired in the formation of AM and root nodule symbiosis (RNS) revealed a set of common symbiosis genes that encode components of a common signaling network involving calcium spiking. These common symbiosis genes are functionally conserved in AM-forming angiosperms indicating an ancient origin of this pathway.