AtPTR1, a plasma membrane peptide transporter expressed during seed germination and in vascular tissue of Arabidopsis
For the efficient translocation of organic nitrogen, small peptides of two to three amino acids are posited as an important alternative to amino acids. A new transporter mediating the uptake of di- and tripeptides was isolated from Arabidopsis thaliana by heterologous complementation of a peptide transport-deficient Saccharomyces cerevisiae mutant. AtPTR1 mediated growth of S. cerevisiae cells on different di- and tripeptides and caused sensitivity to the phytotoxin phaseolotoxin. The spectrum of substrates recognized by AtPTR1 was determined in Xenopus laevis oocytes injected with AtPTR1 cRNA under voltage clamp conditions. AtPTR1 not only recognized a broad spectrum of di- and tripeptides, but also substrates lacking a peptide bond. However, amino acids, -amino fatty acids or peptides with more than three amino acid residues did not interact with AtPTR1. At pH 5.5 AtPTR1 had an apparent lower affinity (K0.5 = 416 m) for Ala-Asp compared with Ala-Ala (K0.5 = 54 m) and Ala-Lys (K0.5 = 112 m). Transient expression of AtPTR1/GFP fusion proteins in tobacco protoplasts showed that AtPTR1 is localized at the plasma membrane. In addition, transgenic plants expressing the β-glucuronidase (uidA) gene under control of the AtPTR1 promoter demonstrated expression in the vascular tissue throughout the plant, indicative of a role in long-distance transport of di- and tripeptides.
Document Type: Research Article
Affiliations: 1: Molecular Plant Physiology, Institute of Plant Sciences, University of Berne, 3013 Berne, Switzerland, 2: Laboratoire de Biochimie, Université de Neuchâtel, 2007 Neuchâtel, Switzerland, 3: Department of Plant Physiology, RWTH Aachen University, 52056 Aachen, Germany, and 4: Department of Plant Biology, University of Minnesota, Biological Science Center, St Paul, MN 55108, USA
Publication date: November 1, 2004