A phosphate transporter gene from the extra-radical mycelium of an arbuscular mycorrhizal fungus Glomus intraradices is regulated in response to phosphate in the environment

The majority of vascular flowering plants are able to form symbiotic associ ations with arbuscular mycorrhizal fungi. These symbioses, termed arbuscula r mycorrhizas, are mutually beneficial, and the fungus delivers phosphate t o the plant while receiving carbon. In these symbioses, phosphate uptake by the arbuscular mycorrhizal fungus is the first step in the process of phos phate transport to the plant. Previously, we cloned a phosphate transporter gene involved in this process. Here, we analyze the expression and regulat ion of a phosphate transporter gene (GiPT) in the extra-radical mycelium of the arbuscular mycorrhizal fungus Glomus intraradices during mycorrhizal a ssociation with carrot or Medicago truncatula roots. These analyses reveal that GiPT expression is regulated in response to phosphate concentrations i n the environment surrounding the extra-radical hyphae and modulated by the overall phosphate status of the mycorrhiza. Phosphate concentrations, typi cal of those found in the soil solution, result in expression of GiPT These data imply that G. intraradices can perceive phosphate levels in the exter nal environment but also suggest the presence of an internal phosphate sens ing mechanism.