The Arabidopsis L-Type Amino Acid Transporter 5 (LAT5/PUT5) Is Expressed in the Phloem and Alters Seed Nitrogen Content When Knocked Out.

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, , under various growth conditions. The mutant seedlings showed increased sensitivity to exogenous leucine in Murashige and Skoog growth medium. In soil, the 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 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.