Siliques Are Red1 from Arabidopsis Acts as a Bidirectional Amino Acid Transporter That Is Crucial for the Amino Acid Homeostasis of Siliques    

Abstract

Many membrane proteins are involved in the transport of nutrients in plants. While the import of amino acids into plant cells is, in principle, well understood, their export has been insufficiently described. Here, we present the identification and characterization of the membrane protein Siliques Are Red1 (SIAR1) from Arabidopsis (Arabidopsis thaliana) that is able to translocate amino acids bidirectionally into as well as out of the cell. Analyses in yeast and oocytes suggest a SIAR1-mediated export of amino acids. In Arabidopsis, SIAR1 localizes to the plasma membrane and is expressed in the vascular tissue, in the pericycle, in stamen, and in the chalazal seed coat of ovules and developing seeds. Mutant alleles of SIAR1 accumulate anthocyanins as a symptom of reduced amino acid content in the early stages of silique development. Our data demonstrate that the SIAR1-mediated export of amino acids plays an important role in organic nitrogen allocation and particularly in amino acid homeostasis in developing siliques.

UMAMIT14 is an amino acid exporter involved in phloem unloading in Arabidopsis roots

“…We reasoned that, similar to UMAMIT18 (Ladwig et al , 2012), expressing an amino acid exporter would decrease the accumulation of amino acids taken up by yeast cells. Wild-type cells, harboring all amino acid importers, were used by Ladwig et al (2012), with the caveat that heterologous expression of an exogenous transporter might disturb the expression/activity of endogenous yeast amino acid transporters, several of which are regulated by amino acid levels at the transcriptional and post-transcriptional levels (Stanbrough and Magasanik, 1995; Didion et al , 1996; Springael and Andre, 1998). To circumvent this problem, UMAMIT14 was co-expressed with the plant amino acid importer AAP3 (Fischer et al , 1995), which is unlikely to be regulated by the general amino acid control or the nitrogen catabolite repression systems of yeast.…”

“…Arabidopsis Bidirectional Amino Acid Transporter 1 (AtBAT1) has been shown to mediate import of GABA, Arg, and Ala, and export of Lys and Glu at the mitochondrion membrane (Dundar and Bush, 2009; Michaeli et al , 2011). Siliques Are Red1 (SiAR1) has been characterized as a bi-directional amino acid transporter responsible for amino acid accumulation in developing siliques (Ladwig et al , 2012). SiAR1/UMAMIT18 is a member of the Usually Multiple Acids Move In and out Transporters family [UMAMIT, also called Medicago truncatula Nodulin 21 (MtN21); Denancé et al , 2014], belonging to the Drug/Metabolite Transporter superfamily.…”

Spatial and temporal transcriptome changes occurring during flower opening and senescence of the ephemeral hibiscus flower,Hibiscus rosa-sinensis

“…Homologues of nodulin genes are found in the genomes of several plants that are unable to nodulate, highlighting an ancestral role in plant physiology (Denancé et al , 2014). An MtN21 protein-encoding gene has recently been proposed to act as a vacuolar auxin export facilitator in isolated Arabidopsis vacuoles (Ranocha et al , 2013), as a bidirectional amino acid transporter (Ladwig et al , 2012), and as a tonoplast-localized protein required for proper secondary cell wall formation (Ranocha et al , 2010). Combined with the induction of the auxin receptor, auxin-binding protein, and the several auxin regulated and induced proteins (AUX/IAA), auxin signalling might be involved in flower opening and senescence possibly by facilitating cell wall remodelling (Paque et al , 2014).…”

Peering into the separate roles of root and shoot cytosolic glutamine synthetase 1;2 by use of grafting experiments in Arabidopsis

“…A high flux of N to juvenile inflorescences is essential for ensuring that a high number of the initiated primordia develop into fertile siliques with a high number of seeds. 6,11 Gln1;2 may be critical for controlling the flux of N to the developing inflorescences and siliques within a fairly narrow time window in which the final yield components are established.…”