Abstract
The amino acid permease (AAP) is an important transmembrane protein that is involved in the absorption and transport of amino acids in plants. We investigated the expression patterns of AtAAP genes in Arabidopsis thaliana, based on quantitative real-time PCR. The results revealed differential expression patterns of eight AtAAP genes in different tissues, with five genes (AtAAP1, AtAAP2, AtAAP6, AtAAP7, and AtAAP8) expressed at relatively high levels in both flowers and siliques, suggesting their shared functions in the accumulation of amino acids. In transgenic plants, with endosperm-specific overexpression of AtAAP1, both AtAAP1 and AtAAP6 were up-regulated in both the roots and siliques, while AtAAP2, AtAAP3, AtAAP4, and AtAAP5 showed similar expression levels in the stems and siliques, whereas AtAAP7 and AtAAP8 were expressed at their highest levels in the stems and roots. The results of the amino acid affinity experiments revealed varied absorption capacities for different amino acids, by AtAAP1, and increased acid amino contents in the reproductive organs. These results were verified in transgenic maize plants, with the overexpression of AtAAP1, revealing higher amino acid contents in the reproductive organs than those of the vegetative organs. Our study clearly demonstrated that the endosperm-specific promoter increased the amino acid contents in the reproductive organs and improved the effective utilization of organic nitrogen in plants.
Highlights
Nitrogen plays an important nutritional role for many organisms, generally for the synthesis of hormones, nucleotides, and amino acids [1]
Four genes (i.e., AtAAP2, AtAAP3, AtAAP6, and AtAAP7) were relatively highly expressed in leaves, flowers, and siliques, two genes (AtAAP1 and AtAAP8) were relatively highly expressed in flowers and siliques, gene AtAAP4 was highly expressed in stems, and gene AtAAP5 showed relatively high expression in both leaves and flowers
Our results revealed that both AtAAP1 and AtAAP8 were highly expressed in the flowers and siliques, while AtAAP2, AtAAP3, and AtAAP5 were highly expressed in the leaves
Summary
Nitrogen plays an important nutritional role for many organisms, generally for the synthesis of hormones, nucleotides, and amino acids [1]. Plants are rich in usable forms of nitrogen, which are commonly found as organic nitrogen in amino acids, nucleic acids, and proteins. The APC superfamily contains five families, i.e., the APC, the amino acid permease (AAP), the alanine and glycine protein cationic symporter (AGCS), the potassium ion and chloride ion transporters (CCC), and the hydroxy/aromatic amino acid permease (HAAAP) families. As the two widely studied families of the APC superfamily, the APC family includes the cationic amino acid transporters (CATs), the amino acid/choline transporters (ACTs), and the polyH transporters (PHSs), while the AAAP family contains the amino acid permeases (AAPs), the lysine and histidine transporters (LHTs), the proline transporters (ProTs), the auxin transport protein (AUXs), and the aromatic and neutral amino acid transporters (ANTs). The physiological functions of these amino acid transporters remain unclear
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