Amino acid permeases in developing seeds ofVicia fabaL.: expression precedes storage protein synthesis and is regulated by amino acid supply

Abstract

SummaryFull length cDNAs encoding three amino acid permeases were isolated from seed-speci®c libraries of Vicia faba. The predicted proteins VfAAP1, VfAAP3 and VfAAP4 share up to 66% identity among themselves. Functional characterization of VfAAP1 and VfAAP3 in a yeast mutant showed that these permeases transport a broad range of amino acids. However, VfAAP1 had a preference for cysteine and VfAAP3 for lysine and arginine. VfAAP1 was highly expressed in cotyledons at early developmental stages and moderately in other sink tissues. Its peak of expression in cotyledons corresponded to the appearance of storage protein transcripts, suggesting that this transporter ful®lls an important role in providing amino acids for storage protein biosynthesis. VfAAP3 was expressed most abundantly in maternal tissues, that is in roots, stems, gynoecia, pods and seed coats at different developmental stages. VfAAP4 transcripts could not be detected by northern hybridization. In situ hybridization showed that VfAAP1 mRNA is distributed throughout cotyledon storage parenchyma cells, but could not be detected in the abaxial epidermal cell layer. It also accumulate in the chlorenchyma and thin-walled parenchyma cells of seed coats. VfAAP1 mRNA levels were lower in cotyledons cultured in the presence of glutamine, whereas expression of a vicilin storage protein gene was up-regulated under similar conditions. Cysteine repressed the expression of the GUS reporter gene under control of the VfAAP1 promoter, suggesting that this transporter is modulated at the transcriptional level. Regulation of amino acid transport in relation to storage protein accumulation is discussed.

High Affinity Amino Acid Transporters Specifically Expressed in Xylem Parenchyma and Developing Seeds of Arabidopsis

“…It could be shown that the expression of the amino acid transporter in seeds precedes the expression of the storage protein AtS1 in Arabidopsis (11). A similar increase in the expression of a legume amino acid transporter has been shown recently in Vicia faba (12). In pea it has been demonstrated that PsAAP1 is expressed in the transfer cell layer of cotyledons and might be responsible for taking up amino acids released from the seed coat (13).…”

Analysis of theArabidopsis O-Acetylserine(thiol)lyase Gene Family Demonstrates Compartment-Specific Differences in the Regulation of Cysteine Synthesis

“…Leustek and Saito, 1999;Kopriva, 2006). Directed transport of Cys across the organelle envelopes was simply assumed and thought to be performed by transport proteins with limited specificity, such as the transporters involved in the uptake of amino acid at the plasmalemma (Miranda et al, 2001;Fischer et al, 2002). However, direct evidence for the transport of Cys between cytosol and compartments is scarce.…”

The Metabolic Role of the Legume Endosperm: A Noninvasive Imaging Study

“…The switch to an active uptake system occurs rather late in development and is based on enhanced levels of AAP1 (an amino acid permease) and PTR1 (a peptide transporter) in the embryo proper (Miranda et al, 2001). This transport system appears to be controlled by assimilate availability (Bennett and Spanswick, 1983).…”