Overexpression of foxtail millet (Setaria italica) amino acid permease 9 ( SiAAP9 ) inhibits the growth in transgenic Arabidopsis

Abstract

Abstract Amino acid permeases (AAPs) transporters play a vital role in facilitating the long-distance transportation of amino acids from the source to the sink in plants. Numerous studies have been conducted on Arabidopsis and rice, while the research on foxtail millet remains relatively scarce. In this study, we discovered that SiAAP9 exhibits two transcripts. The expression patterns of the two transcripts of SiAAP9 were generally consistent and both transcripts were induced by NO3-. Overexpression of SiAAP9L and SiAAP9S in Arabidopsis inhibited plant growth and seed size, however, SiAAP9 can transport more amino acids into seeds. Moreover, the tolerance of WT and SiAAP9-OX transgenic Arabidopsis to amino acids demonstrated that SiAAP9-OX transgenic Arabidopsis lines exhibit tolerance to high concentrations of glutamate (Glu) and histidine (His). The high expression level of SiAAP9 makes its encoded protein not only localized on the plasma membrane, but also possibly localized on various organelles. Additionally, we also observed that sequence deletion weakened the sensitivity of SiAAP9 to Brefeldin A (BFA) and SiAAP9 has ectopic localization on endoplasmic reticulum (ER). Protoplast amino acid uptake experiments indicated that SiAAP9 is capable of facilitating increased transport of Glu into foxtail millet cells. Taken together, the functions of two SiAAP9 transcripts are largely functional similar, but the degree of colocalization of SiAAP9L and BFA compartment is significantly higher than that of SiAAP9S. Our research may provide a candidate gene to improve foxtail millet nutritional quality in breeding.