Alternative splicing analysis of wheat glutamine synthase genes

Abstract

<p id="C3">As a key enzyme for nitrogen assimilation in plant, glutamine synthetase (TaGS) is encoded by 12 genes in common wheat (<italic>Triticum aestivum</italic> L.), namely <italic>TaGS1;1-6A/6B/6D</italic>, <italic>TaGS1;2-4A/4B/4D</italic>, <italic>TaGS1;3-4A/4B/4D</italic>, and <italic>TaGS2-2A/2B/2D</italic>. Transcripts of TaGS genes were obtained using the single molecular sequencing technology, and the results showed that <italic>TaGS1;1-6A</italic> had one alternative splicing (AS) version of transcripts and <italic>TaGS1;1-6B</italic> had two AS versions. Compared with the TaGS encoded by normal transcript, TaGS1;1-6A-1 lacked part of the Gln_synt_N domain, and TaGS1;1-6B-3 lacked the Gln_synth_gly_rich_ site domain; <italic>TaGS1;1-6B-4 </italic>was a new AS event, and encoded a truncated GS without Gln_synth_gly_rich_site and Gln_synth_ cat_dom domain. The relative expression level of TaGS alternative splicing transcripts of wheat cultivars with different nitrogen use efficiencies showed that the relative expression level of <italic>TaGS1;1-6A-1 </italic>in leaves of YM49 (N-efficient) was significantly higher than that of XN509 (N-inefficient), and increased with the increase of nitrogen supply. In roots, the relative expression of <italic>TaGS1;1-6A-1</italic> increased with the increase of nitrogen supply in YM49, but decreased in XN509. <italic>TaGS1;1-6B-3</italic> showed a similar expression trend in YM49 and XN509, and high concentration of NO₃^- promoted the expression of <italic>TaGS1;1-6B-3</italic> in leaves while inhibited in roots. High concentration of NH₄⁺ inhibited the expression of <italic>TaGS1;1-6B-3</italic> in leaves, but had little effect in roots. <italic>TaGS1;1-6B-4</italic> was mainly expressed under low nitrogen condition, and its expression in roots of YM49 was not affected by NH₄⁺ supply. Understanding the AS transcript versions of TaGS genes is helpful to illustrate the functions of TaGS isozymes in nitrogen metabolism of wheat.