Abstract
Amino acid transporters have roles in amino acid uptake from soil, long-distance transport, remobilization from vegetative tissues and accumulation in grain. Critically, the majority of wheat grain nitrogen is derived from amino acids remobilized from vegetative organs. However, no systematic analysis of wheat AAT genes has been reported to date. Here, 283 full length wheat AAT genes representing 100 distinct groups of homeologs were identified and curated by selectively consolidating IWGSC CSSv2 and TGACv1 Triticum aestivum genome assemblies and reassembling or mapping of IWGSC CSS chromosome sorted reads to fill any gaps. Gene expression profiling was performed using public RNA-seq data from root, leaf, stem, spike, grain and grain cells (transfer cell (TC), aleurone cell (AL), and starchy endosperm (SE)). AATs highly expressed in roots are good candidates for amino acid uptake from soil whilst AATs highly expressed in senescing leaves and stems may be involved in translocation to grain. AATs in TC (TaAAP2 and TaAAP19) and SE (TaAAP13) may play important roles in determining grain protein content and grain yield. The expression levels of AAT homeologs showed unequal contributions in response to abiotic stresses and development, which may aid wheat adaptation to a wide range of environments.
Highlights
Grain yield and protein content are dependent upon nitrogen accumulation in the grain
The amino acid/auxin permeases (AAAP) subfamily can be further divided into general amino acid permeases (AAPs), lysine-histidine transporters (LHTs), proline transporters (ProTs), gamma-aminobutyric acid transporters (GATs), aromatic and neutral amino acid transporters (ANTs) and indole-3-acetic acid transporters (AUXs)
In order to identify the amino acid transporters (AATs) presently found in IWGSC CSSv2 (Ensembl v30), the annotations were searched for amino acid transporter domains
Summary
Grain yield and protein content are dependent upon nitrogen accumulation in the grain. Plasma membrane transporters for amino acids are required for root uptake, xylem loading in the roots, phloem loading in leaves, and for nitrogen import into seeds. AtAAP1 is highly expressed in the epidermal layer and embryo of seeds and regulates amino acid import to the embryo[18, 19]. AtAAP8 plays an important role in the uptake of amino acids into the endosperm during early seed development[20]. AtAAP3 and AtAAP5, which are expressed in Arabidopsis root vascular tissue and in all root tissues, respectively, may be involved in amino acid uptake from soil[21, 22]. AtANT1, as an aromatic and neutral amino acid transporter, is expressed in all organs with the most abundance in flowers and in cauline leaves[32]
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