Arabidopsis thaliana Ureide Permease 5 (AtUPS5) connects cell compartments involved in Ureide metabolism.

Allantoin is a purine oxidative product that serves for long distance transport of organic nitrogen in nodulating legumes and was recently related with stress tolerance in other plants. The subcellular localization of enzymes that lead to allantoin synthesis and degradation indicates that allantoin is produced in peroxisomes and degraded in the endoplasmic reticulum (ER). Although it has been determined that allantoin is mostly synthesized in roots and transported to shoots either for organic nitrogen translocation in legumes or for plant protection during stress in Arabidopsis, the mechanism and molecular components for allantoin export from root cells is still unknown. AtUPS5 (Arabidopsis thaliana Ureide Permease 5) is a transmembrane protein that transports allantoin with high affinity when expressed in yeast. The subcellular fate of splicing variants AtUPS5L (Long) and AtUPS5S (Short) was studied by tagging them with fluorescent proteins in their cytosolic loops. The capability of these fusion proteins to complement the function of the native proteins was demonstrated by nutritional and salt stress experiments. Both variants were localized in the ER, but the AtUPS5L variant was also detected in the trans-Golgi network/early endosome (TGN/EE) and at the plasma membrane. AtUPS5L and AtUPS5S localization indicates that they could have different roles in allantoin distribution between subcellular compartments. Our data predict that under non-stress conditions UPS5L and UPS5S may function in allantoin degradation pathway for nutrient recycling, whereas under stress, both genes would be involved in cell export via vesicles of the secretory pathway allowing allantoin translocation from roots to shoots.