Poster: Membrane Transport
Abs #
1203: Transport of Nucleobases and Derivatives by the Arabidopsis thaliana family of Ureide Permeases (AtUPS)
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Presenter: |
Schmidt, Anja , anja.schmidt@zmbp.uni-tuebingen.de |
Authors | Schmidt, Anja (A) Su, Yanhua (A) Hilpert, Melanie (A) Ludewig, Uwe (A) Frommer, Wolf B. (A) Desimone, Marcelo (A) | | Affiliations: |
(A): University of Tuebingen; Zentrum fuer Molekularbiologie der Pflanzen
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Nucleobases and their derivatives are crucial for growth and survival of plants. This is obvious regarding the composition of RNA and DNA. In addition, because of their molecular composition, they serve as sources, storage- and transport-forms of nitrogen, a limiting element in plants. Despite this, knowledge about uptake and transport of these substances is still scarce. Recently, a transporter for allantoin and other oxo-N-heterocycles was described in Arabidopsis. AtUPS1 belongs to a protein family with five conserved members in Arabidopsis and related genes in various other plant species, eg. cowpea, tomato and rice. To better understand their role in transport of nucleobases and related compounds, a detailed characterization of AtUPS1 and AtUPS2 concerning substrate specificity and mechanism of action was performed after expression in Xenopus oocytes and a yeast knockout strain deficient in allantoin uptake. These studies showed that several substrates including cyclic purine degradation products and pyrimidines are transported in a proton-coupled manner. The presence of a Walker A motif in the AtUPS1 sequence suggests a potential regulatory role for binding of ATP or GTP in transport. To explore this possibility, site directed mutagenesis was carried out. Amino acid replacement in key residues of the conserved motif leads to decreased allantoin transport when expressed in Xenopus oocytes.
To determine spacial and temporal changes in transcriptional activities, studies of promotor regions using Uida as reporter gene were performed. While AtUPS1 seems to be mainly present in young seedlings and repressed by NH4+, AtUPS2 and AtUPS5 are currently analyzed as candidates for the uptake of N-heterocycles from soil.
