Characterization and expression of French bean amino acid transporter PvAAP1 Qiumin Tan a , Aleel K. Grennan a,1 , He ´le `ne C. Pe ´lissier a , Doris Rentsch b , Mechthild Tegeder a, * a School of Biological Sciences, Center for Integrated Biotechnology, Center for Reproductive Biology, Washington State University, Abelson 315, Pullman, WA 99164, USA b Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland Received 16 October 2007; received in revised form 20 December 2007; accepted 20 December 2007 Available online 11 January 2008 Abstract 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. # 2008 Elsevier Ireland Ltd. All rights reserved. Keywords: Phaseolus vulgaris; Amino acid transporter; RNA localization; Assimilate partitioning; Phloem and seed loading 1. Introduction Plants acquire nitrogen in different ways. Inorganic or organic forms of nitrogen are taken up by the roots or, in the case of nodulated legume roots, atmospheric nitrogen is fixed in a bacteria–plant relationship. In most plant species, inorganic nitrogen is reduced to amino acids, however, in the nodules of tropical legumes such as Phaseolus vulgaris (French bean) and Glycine max (soybean) the ureides allantoin and allantoic acid are also synthesized [1,2]. Following synthesis, organic nitrogen is distributed via the vascular bundles to plant organs, where it is used for growth or storage (sinks). While root to shoot transport of the nitrogen compounds occurs in the xylem [3–5], distribution to sinks generally is via the phloem [6–8]. Ureides and amides that are synthesized in the root nodules and delivered within the xylem to the shoot/source leaves are metabolized, transiently accumulated or immediately trans- ferred, without metabolism, to the phloem to supply sinks such as seeds [7,8]. In addition, the organic nitrogen might be transferred from the xylem to the phloem to be directly distributed to pods or seeds. Dependent on the developing stage, ureides are metabolized to amino acids in the pod wall or in the seed coat [7] and the amino acids are finally released into the seed apoplast by the seed coat followed by uptake into the embryo/cotyledons that are symplasmically isolated. These partitioning and seed loading processes require ureide and/or amino acid transporters that effectively deal with the amount of the organic nitrogen compounds and the speed at which the www.elsevier.com/locate/plantsci Available online at www.sciencedirect.com Plant Science 174 (2008) 348–356 * Corresponding author. Tel.: +1 509 335 7545; fax: +1 509 335 3184. E-mail address: tegeder@wsu.edu (M. Tegeder). 1 Current address: University of Illinois, Urbana, IL 61801, USA. 0168-9452/$ – see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2007.12.008