AAP7 | GeneID:832446 | Arabidopsis thaliana

NM_001036857   NM_122286  

BAB10054   BAH19694   CAV27491   NP_001031934   NP_197770  

• At.26436 cluster

1. [ ] Okumoto S, et al. (2002) "High affinity amino acid transporters specifically expressed in xylem parenchyma and developing seeds of Arabidopsis." J Biol Chem. 277(47):45338-45346. PMID:12244056

Arabidopsis amino acid transporters (AAPs) show individual temporal and spatial expression patterns. A new amino acid transporter, AAP8 was isolated by reverse transcription-PCR. Growth and transport assays in comparison to AAP1-5 characterize AAP8 and AAP6 as high affinity amino acid transport systems from Arabidopsis. Histochemical promoter-beta-glucuronidase (GUS) studies identified AAP6 expression in xylem parenchyma, cells requiring high affinity transport due to the low amino acid concentration in xylem sap. AAP6 may thus function in uptake of amino acids from xylem. Histochemical analysis of AAP8 revealed stage-dependent expression in siliques and developing seeds. Thus AAP8 is probably responsible for import of organic nitrogen into developing seeds. The only missing transporter of the family AAP7 was nonfunctional in yeast with respect to amino acid transport, and expression was not detectable. Therefore, AAP6 and -8 are the only members of the family able to transport aspartate with physiologically relevant affinity. AAP1, -6 and -8 are the closest AAP paralogs. Although AAP1 and AAP8 originate from a duplicated region on chromosome I, biochemical properties and expression pattern diverged. Overlapping substrate specificities paired with individual properties and expression patterns point to specific functions of each of the AAP genes in nitrogen distribution rather than to mere redundancy.

2. [ ] Fischer WN, et al. (1995) "Substrate specificity and expression profile of amino acid transporters (AAPs) in Arabidopsis." J Biol Chem. 270(27):16315-16320. PMID:7608199

Three amino acid transporter genes (AAP3-5) were isolated from Arabidopsis by complementation of a yeast mutant defective in histidine uptake. Transport is driven against a concentration gradient and sensitive to protonophores. Analysis of the substrate specificity demonstrates that the carriers have a broad substrate specificity covering the major transport forms of reduced nitrogen, i.e. glutamine and glutamate. The transporters have similar affinities for glutamate, glutamine, and alanine but differ with respect to valine, phenylalanine, histidine, arginine, and lysine. AAP3 and AAP5 efficiently transport arginine and lysine and are involved in basic amino acid transport. The predicted polypeptides of 53 kDa are highly hydrophobic with 12 putative membrane-spanning regions and show significant homologies to Arabidopsis amino acid transporters AAP1 and AAP2. Each of the genes has a different organ-specific expression in the plant. AAP3 is exclusively expressed in roots and AAP4 mainly in source leaves, stems, and flowers, whereas AAP5 is found in all tissues. The specific distribution in the plant and the different substrate specificities of AAP transporters may indicate that tissues differ both qualitatively and quantitatively regarding import or export of amino acids.