title: The putative Cationic Amino Acid Transporter 9 is targeted to vesicles and may be involved in plant amino acid homeostasis.
abstract: Amino acids are major primary metabolites. Their uptake, translocation, compartmentation, and re-mobilization require a diverse set of cellular transporters. Here, the broadly expressed gene product of CATIONIC AMINO ACID TRANSPORTER 9 (CAT9) was identified as mainly localized to vesicular membranes that are involved in vacuolar trafficking, including those of the trans-Golgi network. In order to probe whether and how these compartments are involved in amino acid homeostasis, a loss-of-function cat9-1 mutant and ectopic over-expressor plants were isolated. Under restricted nitrogen supply in soil, cat9-1 showed a chlorotic phenotype, which was reversed in the over-expressors. The total soluble amino acid pools were affected in the mutants, but this was only significant under poor nitrogen supply. Upon nitrogen starvation, the soluble amino acid leaf pools were lower in the over-expressor, compared with cat9-1. Over-expression generally affected total soluble amino acid concentrations, slightly delayed development, and finally improved the survival upon severe nitrogen starvation. The results potentially identify a novel function of vesicular amino acid transport mediated by CAT9 in the cellular nitrogen-dependent amino acid homeostasis.
authors.affiliation: Nutritional Crop Physiology, Institute of Crop Science, University of Hohenheim Stuttgart, Germany.
authors.forename: Huaiyu
authors.initials: H
authors.lastname: Yang
authors.affiliation: Zentrum für Molekularbiologie der Pflanzen, University of Tübingen Tübingen, Germany.
authors.forename: York-Dieter
authors.initials: YD
authors.lastname: Stierhof
authors.affiliation: Nutritional Crop Physiology, Institute of Crop Science, University of Hohenheim Stuttgart, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Ludewig
keywords: amino acid permease; cationic amino acid; nitrogen; prevacuole; trans-Golgi network