Mycorrhizal phosphate uptake pathway in tomato is phosphorus-repressible and transcriptionally regulated

Plants colonized by arbuscular mycorrhizal (AM) fungi take up phosphate (Pi) via the mycorrhizal and the direct Pi uptake pathway. Our understanding of the molecular mechanisms involved in the regulation of these pathways is just emerging. Here, we have analyzed the molecular physiology of mycorrhizal Pi uptake in the tomato (Solanum lycopersicum) variety Micro-Tom and integrated the data obtained with studies on chemical signaling in mycorrhiza-inducible Pi transporter gene regulation. At high plant phosphorus (P) status, the mycorrhizal Pi uptake pathway was almost completely repressed and the mycorrhiza-inducible Pi transporter genes were down-regulated. A high plant P status also suppressed the activation of the mycorrhiza-specific StPT3 promoter fragment by phospholipid extracts containing the mycorrhiza signal lysophosphatidylcholine. Our results suggest that the mycorrhizal Pi uptake pathway is controlled at least partially by the plant host. This control involves components in common with the regulatory mechanism of the Pi starvation response pathway in plants. New Phytologist (2009) 181: 950-959doi: 10.1111/j.1469-8137.2008.02721.x.