The spatial expression patterns of a phosphate transporter (MtPT1) from Medicago truncatula indicate a role in phosphate transport at the root/soil interface

The movement of phosphate from the soil into plant root cells is the first of many crucial transport events required to supply phosphorous (P) to cell s throughout the plant. In addition to the ability to acquire phosphate fro m the soil, the majority of the vascular plants are able to form arbuscular mycorrhizal associations in which phosphate may be delivered to the cortex via a fungus. Previously, we cloned two phosphate transporter genes, MtPT1 and MtPT2 from Medicago truncatula roots. Complementation of a yeast phosp hate transport mutant revealed that MtPT1 is a functional phosphate transpo rter and Northern analyses revealed that MtPT1 is expressed exclusively in roots (Liu et al., 1998, Mol. Plant-Microbe Interact. 11, 14-22). Utilising an antibody specific for MtPT1, we have analysed the accumulation and spat ial expression patterns of the MtPT1 transporter. MtPT1 transcript and prot ein levels show close correlation and increase dramatically in the roots in response to phosphate starvation. MtPT1 protein levels decrease in roots d uring development of a symbiosis with arbuscular mycorrhizal (AM) fungi, in dicating that this transporter is not involved in symbiotic phosphate trans port. Membrane fractionation and analysis of a MtPT1/GFP fusion protein rev ealed that MtPT1 is located in the plasma membrane, while in situ hybridisa tion and immunolocalisation demonstrate the presence of MtPT1 transcripts a nd protein in the epidermal cells and root hairs of M. truncatula roots. Mt PT1 shows expression patterns consistent with a role specifically in the ac quisition of phosphate from the soil and is distinct from the other phospha te transporter of this class described to date.