Tomato sugar transporter genes associated with mycorrhiza and phosphate

Abstract

In arbuscular mycorrhizal (AM) symbiosis, there is a reciprocal nutrient exchange between symbiotic partners. AM fungi assist the plants with uptake of mineral nutrients from the soil, especially phosphate (Pi). The host plants, in return, provide the fungi with sugar. In contrast to the studies on the symbiotic transport of Pi in arbuscular mycorrhiza, there have been few investigations devoted specifically to sugar transport in AM symbiosis. Using reverse transcriptase PCR (RT-PCR), we analyzed the effects of mycorrhiza and Pi on the expression of seven putative sugar transporter genes in tomato plants. The expression of LeSUT1 and LeHT2, classified, respectively, as putative sucrose and hexose transporter genes, were down-regulated in the roots inoculated with AM fungi Glomus caledonium or Glomus intraradices. Unexpectedly, the expression of LeST3, a putative monosaccharide transporter gene, was decreased by inoculation of Glomus caledonium, but was enhanced by inoculation of Glomus intraradices in both the roots and leaves. High-Pi in the tomato decreased the expression of LeHT2 and LeST3 in the roots, and enhanced that of LeHT2 in the leaves. The contradictory regulation of the expression of LeST3 in the AM symbiosis indicates that different interaction may take place during mycorrhizal colonization, and a quite complicated regulation of expression of the sugar transporter genes exist in mycorrhizal tomato.