A phosphate transporter expressed in arbuscule-containing cells in potato

Arbuscular mycorrhizas are the most common non-pathogenic symbioses in the roots of plants. It is generally assumed that this symbiosis facilitated th e colonization of land by plants(1). In arbuscular mycorrhizas, fungal hyph ae often extend between the root cells and tuft-like branched structures (a rbuscules) form within the cell lumina that act as the functional interface for nutrient exchange. In the mutualistic arbuscular-mycorrhizal symbiosis the host plant derives mainly phosphorus from the fungus, which in turn be nefits from plant-based glucose(2). The molecular basis of the establishmen t and functioning of the arbuscular-mycorrhizal symbiosis is largely not un derstood. Here we identify the phosphate transporter gene StPT3 in potato ( Solanum tuberosum). Functionality of the encoded protein was confirmed by y east complementation. RNA localization and reporter gene expression indicat ed expression of StPT3 in root sectors where mycorrhizal structures are for med. A sequence motif in the StPT3 promoter is similar to transposon-like e lements, suggesting that the mutualistic symbiosis evolved by genetic rearr angements in the StPT3 promoter.