Poster: Membrane Transport

Abs # 1236: Characterization of the first ureide transporter found in legumes

Presenter:	Pelissier, Helene C, hpelissi@mail.wsu.edu
Authors	Pelissier, Helene C (A)   Frerich, Anke  (A)   Desimone, Marcello  (B)   Tegeder, Mechthild  (A)
Affiliations:	(A): School of Biological Sciences, Center for Reproductive Biology, Center of Integrated Biotechnology, Washington State University, Pullman (B): University of Tuebingen, ZMBP

Nodulated legumes receive their nitrogen via N-fixing rhizobia which exist in a symbiotic relationship with the root system. In tropical legumes like soybean, chick pea or French bean, most of the fixed nitrogen is reduced to the ureides allantoin and allantoic acid, the major long-distance transport forms of organic nitrogen in these species. Ureide distribution has been investigated at the physiological level in different legumes but molecular data on transport is totally lacking. To understand the underlying mechanism of ureide transport and its regulation, an allantoin transporter (PvUPS1) was isolated from cDNA of nodulated roots of French bean (Phaseolus vulgaris) and functionally characterized in an allantoin transport-deficient yeast mutant showing that PvUPS1 transports allantoin but also recognizes the heterocylic derivates xanthine, uric acid and hydantoin. In plants, PvUPS was found to be expressed throughout the plant body. In roots, the expression level was dependent on the status of nodulation, with highest expression in nodulated roots compared to non-nodulated roots supplied with ammonium nitrate or allantoin. Differences in PvUPS expression in nodulated versus non-nodulated plants could not be detected in other plant organs. Leaf feeding experiments with radioactive allantoin indicate that transport of ureides occurs from source leaves to developing fruits, and uptake studies of allantoin into seed coats confirmed that transport proteins might be involved in this process. (This work is supported by the NRI Competitive Grants Program- USDA grant 2001-35318-10990)