Characterization and expression of French bean amino acid transporter PvAAP1

Nitrogen (N) is essential for plant growth and development. In tropical legumes amino acids and ureides are the main N-transport forms within plants and transporters are necessary to accommodate partitioning of the organic nitrogen. Here, we describe the isolation and functional characterization of an amino acid transporter, PvAAP1 from French bean (Phaseolus vulgaris) and its expression and localization within the plant. Functional complementation of yeast mutants deficient in amino acid transport with a newly constructed bean cDNA expression library from RNA of developing cotyledons resulted in the isolation of PvAAP1. Heterologous expression of PvAAP1 in yeast mutants showed that the transporter mediates cell growth on a broad spectrum of amino acids. RNA expression analysis demonstrated that PvAAP1 is found in all plant organs, and using RNA in situ hybridization experiments PvAAP1 transcripts were localized to the phloem throughout the plant and to stem xylem parenchyma cells. In seeds, PvAAP1 was detected in the outer-epidermal cells of the developing cotyledons (embryos). Together, the yeast experiments and RNA expression and localization studies suggest a role of PvAAP1 in xylem-phloem transfer and phloem loading for amino acid transport to sinks as well as in amino-N import into the cotyledons for seed development and storage compound accumulation.