AZG1 is a cytokinin transporter that interacts with auxin transporter PIN1 and regulates the root stress response.

An environmentally responsive root system is crucial for plant growth and crop yield, especially in suboptimal soil conditions. This responsiveness enables the plant to exploit regions of high nutrient density while simultaneously minimizing abiotic stress. Despite the vital importance of root systems in regulating plant growth, significant gaps of knowledge exist in the mechanisms that regulate their architecture.

Arabidopsis AZG2 transports cytokinins in vivo and regulates lateral root emergence.

Cytokinin and auxin are key regulators of plant growth and development. During the last decade transport mechanisms have turned out to be the key for the control of local and long-distance hormone distributions. In contrast with auxin, cytokinin transport is poorly understood.

Ureide metabolism in Arabidopsis thaliana is modulated by C:N balance.

Plants can respond and adapt to changes in the internal content of carbon and nitrogen by using organic compounds that widely differ in their carbon/nitrogen ratio. Among them, the amides asparagine and glutamine are believed to be preferred by most plants, including Arabidopsis. However, increases in the ureides allantoin and/or allantoate concentrations have been observed in different plant species under several environmental conditions.

Ureide Permease 5 (AtUPS5) Connects Cell Compartments Involved in Ureide Metabolism.

Allantoin is a purine oxidative product involved in long distance transport of organic nitrogen in nodulating legumes and was recently shown to play a role in stress tolerance in other plants. The subcellular localization of enzymes that catalyze 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 of allantoin export from root cells are still unknown.

Allantoin accumulation mediated by allantoinase downregulation and transport by Ureide Permease 5 confers salt stress tolerance to Arabidopsis plants.

Allantoin, a metabolite generated in the purine degradation pathway, was primarily considered an intermediate for recycling of the abundant nitrogen assimilated in plant purines. More specifically, tropical legumes utilize allantoin and allantoic acid as major nodule-to-shoot nitrogen transport compounds. In other species, an increase in allantoin content was observed under different stress conditions, but the underlying molecular mechanisms remain poorly understood.

Heterologous expression of a plant uracil transporter in yeast: improvement of plasma membrane targeting in mutants of the Rsp5p ubiquitin protein ligase.

Plasma membrane proteins involved in transport processes play a crucial role in cell physiology. On account of these properties, these molecules are ideal targets for development of new therapeutic and agronomic agents. However, these proteins are of low abundance, which limits their study.

Comparative studies on Ureide Permeases in Arabidopsis thaliana and analysis of two alternative splice variants of AtUPS5.

The recovery of free purine and pyrimidine bases and their degradation products represent alternative pathways in plant cells either to synthesize nucleotides (salvage pathways) by low energy consumption or to reuse organic nitrogen. Such recycling of metabolites often requires their uptake into the cell by specialized transport systems residing in the plasma membrane. In plants, it has been suggested that several protein families are involved in this process, but only a few transporters have so far been characterized.

Transcription analysis of arabidopsis membrane transporters and hormone pathways during developmental and induced leaf senescence.

A comparative transcriptome analysis for successive stages of Arabidopsis (Arabidopsis thaliana) developmental leaf senescence (NS), darkening-induced senescence of individual leaves attached to the plant (DIS), and senescence in dark-incubated detached leaves (DET) revealed many novel senescence-associated genes with distinct expression profiles. The three senescence processes share a high number of regulated genes, although the overall number of regulated genes during DIS and DET is about 2 times lower than during NS. Consequently, the number of NS-specific genes is much higher than the number of DIS- or DET-specific genes.

UPS1 and UPS2 from Arabidopsis mediate high affinity transport of uracil and 5-fluorouracil.

Salvage pathways play an important role in providing nucleobases to cells, which are unable to synthesize sufficient amounts for their needs. Cellular uptake systems for pyrimidines have been described, but in higher eukaryotes, transporters for thymine and uracil have not been identified. Two plant transporters, AtUPS1 and PvUPS1, were recently identified as transporters for allantoin in Arabidopsis and French bean, respectively.

PvUPS1, an allantoin transporter in nodulated roots of French bean.

Nodulated legumes receive their nitrogen via nitrogen-fixing rhizobia, which exist in a symbiotic relationship with the root system. In tropical legumes like French bean (Phaseolus vulgaris) or soybean (Glycine max), most of the fixed nitrogen is used for synthesis of the ureides allantoin and allantoic acid, the major long-distance transport forms of organic nitrogen in these species. The purpose of this investigation was to identify a ureide transporter that would allow us to further characterize the mechanisms regulating ureide partitioning in legume roots.

ARAMEMNON, a novel database for Arabidopsis integral membrane proteins.

A specialized database (DB) for Arabidopsis membrane proteins, ARAMEMNON, was designed that facilitates the interpretation of gene and protein sequence data by integrating features that are presently only available from individual sources. Using several publicly available prediction programs, putative integral membrane proteins were identified among the approximately 25,500 proteins in the Arabidopsis genome DBs. By averaging the predictions from seven programs, approximately 6,500 proteins were classified as transmembrane (TM) candidate proteins.

Identification of an Arabidopsis mitochondrial succinate-fumarate translocator.

Complementation of a yeast acr1 mutant carrying a deletion of the succinate/fumarate carrier gene enabled functional identification of a mitochondrial succinate translocator from Arabidopsis thaliana (AtmSFC1). Thus complementation of yeast mutants is applicable also for identification and characterization of organellar transporters. Reverse transcription polymerase chain reaction and promoter-GUS fusion showed expression of AtmSFC1 in 2 day old dark grown seedlings, which declined in cotyledons during further development, consistent with a role in export of fumarate for gluconeogenesis during lipid mobilization at early germination of Arabidopsis seeds.

Expression pattern of a nuclear encoded mitochondrial arginine-ornithine translocator gene from Arabidopsis.

Background: Arginine and citrulline serve as nitrogen storage forms, but are also involved in biosynthetic and catabolic pathways. Metabolism of arginine, citrulline and ornithine is distributed between mitochondria and cytosol. For the shuttle of intermediates between cytosol and mitochondria transporters present on the inner mitochondrial membrane are required.

An Arabidopsis thaliana knock-out mutant of the chloroplast triose phosphate/phosphate translocator is severely compromised only when starch synthesis, but not starch mobilisation is abolished.

The Arabidopsis thaliana tpt-1 mutant which is defective in the chloroplast triose phosphate/phosphate translocator (TPT) was isolated by reverse genetics. It contains a T-DNA insertion 24 bp upstream of the start ATG of the TPT gene. The mutant lacks TPT transcripts and triose phosphate (TP)-specific transport activities are reduced to below 5% of the wild type.

A novel superfamily of transporters for allantoin and other oxo derivatives of nitrogen heterocyclic compounds in Arabidopsis.

A wide spectrum of soil heterocyclic nitrogen compounds are potential nutrients for plants. Here, it is shown that Arabidopsis plants are able to use allantoin as sole nitrogen source. By functional complementation of a yeast mutant defective in allantoin uptake, an Arabidopsis transporter, AtUPS1 (Arabidopsis thaliana ureide permease 1), was identified.