Characterization of six PHT1 members in Lycium barbarum and their response to arbuscular mycorrhiza and water stress

Phosphorus (P) is vitally important for most plant processes. However, the P available to plants is present in the soil in the form of inorganic phosphate (Pi), and is often present in only limited amounts. Water stress further reduces Pi availability. Previous studies have highlighted the important roles of members of the PHOSPHATE TRANSPORTER 1 (PHT1) family and arbuscular mycorrhizal (AM) associations for Pi acquisition by plants growing in various environments. In order to understand the Pi uptake of Lycium barbarum L., a drought-tolerant ligneous species belonging to the Solanaceae family, we cloned and characterized six L. barbarum genes encoding transporter proteins belonging to the PHT1 family, and investigated their transcriptional response to AM associations and water stress. The six cloned PHT1 genes of L. barbarum had a similar evolutionary history to that of PHT1 genes found in other Solanaceae species. Three of these genes (LbPT3, LbPT4 and LbPT5) were AM-induced; the other three genes (LbPT1, LbPT2 and LbPT7) played distinct roles in Pi acquisition, translocation and remobilization in roots and leaves. AM-induced PHT1 genes maintained their function under water stress, while moderate and severe water stress upregulated non-AM-induced PHT1 genes in roots and leaves, respectively. Moreover, although LbPT1 was upregulated in AM roots under water stress, LbPT2 and LbPT7 were inhibited in AM roots, which suggested that an AM association satisfied the demand for Pi in roots under water stress and that LbPT1 may play a role in translocating Pi from roots to shoots in this situation.