Abstract
The Arabidopsis L-type Amino Acid Transporter-5 (LAT5; At3g19553) was recently studied for its role in developmental responses such as flowering and senescence, under an assumption that it is a polyamine uptake transporter (PUT5). The LATs in Arabidopsis have a wide range of substrates, including amino acids and polyamines. This report extensively studied the organ and tissue-specific expression of the LAT5/PUT5 and investigated its role in mediating amino acid transport. Organ-specific quantitative RT-PCR detected LAT5/PUT5 transcripts in all organs with a relatively higher abundance in the leaves. Tissue-specific expression analysis identified GUS activity in the phloem under the LAT5/PUT5 promoter. In silico analysis identified both amino acid transporter and antiporter domains conserved in the LAT5/PUT5 protein. The physiological role of the LAT5/PUT5 was studied through analyzing a mutant line, lat5-1, under various growth conditions. The mutant lat5-1 seedlings showed increased sensitivity to exogenous leucine in Murashige and Skoog growth medium. In soil, the lat5-1 showed reduced leaf growth and altered nitrogen content in the seeds. In planta radio-labelled leucine uptake studies showed increased accumulation of leucine in the lat5-1 plants compared to the wild type when treated in the dark prior to the isotopic feeding. These studies suggest that LAT5/PUT5 plays a role in mediating amino acid transport.
Highlights
Plants take up nitrogen in the forms of NO3 −, NH4 +, amino acids, and peptides
In addition to the amino acid permease domain PF13520 reported to be conserved in all five Arabidopsis LATs [11], the L-type Amino Acid Transporter-5 (LAT5)/PUT5 putatively has PotE Amino Acid Transporter (COG0531), Amino Acid Permease (PRK11357), Arginine/Agmatine Antiporter (PRK10644), Arginine/Ornithine Antiporter (TIGR00905), and Glutamate/Gamma-Aminobutyrate Antiporter (TIGR00910) domains conserved in the amino acid sequence (Figure 1b)
Our studies suggested that the LAT5/PUT5 plays a role in amino acid transport, while previous reports indicated that it is a polyamine transporter [17,18]
Summary
Plants take up nitrogen in the forms of NO3 − , NH4 + , amino acids, and peptides. Nitrogen, taken up as NO3 − or NH4 + , is assimilated into amino acids via the Glutamine Synthetase/GlutamateSynthase pathway and moves from the source to sink tissues in the form of amino acids [1,2]. Plants take up nitrogen in the forms of NO3 − , NH4 + , amino acids, and peptides. Plants with various types of source and sink tissues, as well as with various types of protein and non-protein amino acids, require a large number of amino acid transporters with export, import, antiport, or facilitator capacity. These transporters, as they facilitate the movement of amino acids through membranes, regulate the distribution of amino-N in plants. Understanding the distribution of amino-N in plants requires understanding the tissue-specific distribution of amino acid transporters with their substrate affinity and transport mechanism
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