Cell-specific gene expression of phosphate transporters in mycorrhizal tomato roots.

Phosphorus (P) is an essential plant nutrient and is limiting for plant growth in most natural ecosystems as well as in agricultural production throughout the world. In arbuscular mycorrhizal (AM) symbiosis, the fungus obtains carbon from the plant and transfers mineral nutrients, like phosphate (Pi), from the soil to the root cells. Mycorrhizal plants can acquire Pi directly from the soil through plant-specific Pi transporters (the direct uptake pathway) or through fungal uptake and transport systems (the mycorrhizal uptake pathway). The study of plant Pi transporters and of their functioning therefore represents a key point for plant physiology. In this work, after a morphological analysis of tomato mycorrhizal roots, we have used the laser microdissection technology to collect cortical, epidermal, and central cylinder cells with the aim of analyzing the expression of the five so far identified tomato Pi transporter genes in the different root tissues. Using reverse transcriptase PCR analysis, LePT1 and LePT2 transcripts were detected in the epidermal and cortical cells, while LePT3, LePT4, and LePT5 transcripts were confirmed to be exclusive of arbuscule-containing cells. Despite the presence of mRNA in all the analyzed cell populations, no expression of the known tomato Pi transporter genes was observed in the central cylinder cells, irrespective of the presence of the AM fungus.