Nitrogen metabolism and transport in the arbuscular mycorrhizal symbiosis

The arbuscular mycorrhizal (AM) symbiosis between the roots of most land plants is ancient, widespread and central to the mineral nutrition of plants. In return for photosynthetically fixed carbon on which they depend as obligate symbionts, AM fungi take up translocate and transfer much of the phosphate required by their hosts. They also conduct an uncertain fraction of the nitrogen acquired by roots from the soil. With collaborators over the past two decades, we have delineated and explored the operation of the fungal metabolic and transport pathways that conduct these globally enormous fluxes. Despite consensus about the structure of the pathways and steady progress at the molecular level (including the recent publication of an AM fungal genome), much remains to be confirmed and elucidated about the mechanisms and even more about the regulatory processes involved. Basic physiological and ecological questions such as the importance in natural and agricultural ecosystems of the symbiosis for the acquisition by plants of nitrogen remain unanswered.  Controversy continues to reign over the extent of plant-to-plant transfer via AM fungi of fixed carbon and/or nitrogen. This presentation will focus on progress in our group on elucidating the pathways, regulation and importance to plant nutrition of Nitrogen transfer to plants through AM fungi.