Spatiotemporal expression patterns of wheat amino acid transporters reveal their putative roles in nitrogen transport and responses to abiotic stress

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.Grain yield and protein content are dependent upon nitrogen accumulation in the grain. Greater than 70% of wheat grain nitrogen is remobilised and translocated from senescing leaves and stems 1, 2 , and amino acids represent the major transport form of organic nitrogen delivered to the endosperm cavity via the vascular strand 3, 4 . Large quantities of amino acids are imported into grain to meet the high nitrogen demand for synthesis of endosperm storage proteins, and for embryo development.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. Amino acid transporters (AATs) , and other crops [9][10][11] . Based on sequence similarities and uptake properties, amino acid transporter families in plants comprise of two subfamilies: the amino acid/auxin permeases (AAAP) and the amino acid polyamine and choline transporters (APC) [12][13][14][15] . The 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). A new group, amino acid transporter-like (ATL), was recently identified in rice 6 . The APC subfamily is grouped into three further subfamilies: cationic amino acid transporter (CATs), bidirectional acid transporters (BATs) and L-type amino acid transporters (LATs).Within the amino acid transporter family, amino acid permeases (AAPs) have been functionally characterized in Arabidopsis. Eight members (AtAAP1-8) have been identified as amino acid permeases (AAP) that

TaAAP6-3B, a regulator of grain protein content selected during wheat improvement

“…2 ). Previously, the TaAAP family have been mapped to wheat chromosome and it has been named as TaAAP8 [ 15 ].

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“…Wheat GPC is a multigenic-controlled complex trait, and the demand for high-quality cereals as a source of protein has become increased [ 15 ]. So far, only NAM1 gene has been reported to enhance the nutritional value of crops, which was associated with increased GPC in bread wheat [ 1 ].…”

Transcriptomic Analysis of Short-Term Salt Stress Response in Watermelon Seedlings

“…Under salt stress, we identified a total of 45 up-regulated DEGs and 17 down-regulated DEGs associated with amino acid transport function ( Supplementary Materials, Table S6 ). Salt stress induces changes in amino acid compositions, and the enhanced expression of amino acid transporters has been validated in Arabidopsis [ 89 ], rice [ 87 ], and wheat [ 90 ]. The DEGs involved in amino acid transport may play important roles in regulating the partitioning of different amino acids and maintain osmotic potential in response to salt stress.…”

Genome-wide identification of the amino acid permease genes and molecular characterization of their transcriptional responses to various nutrient stresses in allotetraploid rapeseed

“…Environmental stresses lead to AA accumulation in leaves due to the decrease in AA usage for protein biosynthesis or the increase in AA release from protein degradation [55]. The changes in AA composition in the cells in response to environmental stresses results in the expression alterations of AATs [56].…”