Plant nutrient transporter regulation in arbuscular mycorrhizas

This review discusses the role arbuscular mycorrhizal fungi play in the regulation of plant nutrient transporter genes. Many plant nutrient transporter genes appear to be transcriptionally regulated by a feed-back mechanism that reduces their expression when the plant reaches an optimal level of nutrition. Their down-regulation in mycorrhizal roots, therefore, would be predicted as a result of symbiotic function. A variety of studies on Pi- Zn- and ammonium- or nitrate-transporter genes from two plant species indirectly support this model. For example, one study showed that the expression of the high-affinity Pi-transporter MtPT2 within mycorrhizal roots of Medicago truncatulawas inversely correlated with the concentration of P within the shoots, which suggested that P supply from the fungus influenced this gene's expression. However, there is some evidence that these plant nutrient transporters are also down-regulated within mycorrhizal roots by a mechanism not involving nutrient supply by the fungus. Carbon demand by the fungus may be one factor that can influence their expression within mycorrhizal roots.