Evolutionary conservation of a phosphate transporter in the arbuscular mycorrhizal symbiosis.

Arbuscular mycorrhizae are ancient symbioses that are thought to have originated >400 million years ago in the roots of plants, pioneering the colonization of terrestrial habitats. In these associations, a key process is the transfer of phosphorus as inorganic phosphate to the host plant across the fungus-plant interface. Mycorrhiza-specific phosphate transporter genes and their regulation are conserved in phylogenetically distant plant species, and they are activated selectively by fungal species from the phylum Glomeromycota. The potato phosphate transporter gene StPT3 is expressed in a temporally defined manner in root cells harboring various mycorrhizal structures, including thick-coiled hyphae. The results highlight the role of different symbiotic structures in phosphorus transfer, and they indicate that cell-cell contact between the symbiotic partners is required to induce phosphate transport.