Polyploidization plays an important role in the genesis of cultivated wheat (hexaploid and tetraploid) from its diploid progenitors. Thus, evolution during polyploidization resulted in present-day hexaploid bread wheat. GS2 and Fd-GOGAT enzymes are core components involved in the assimilation of primary nitrogen (N) in plants. In the present study, we aimed to analyze these two important genes at their molecular level to find the extent of variation that occurred during evolution from the ancient diploid progenitors to the modern-day hexaploid bread wheat. Furthermore, we studied their gene expression pattern and assayed both the enzymes under N stress. We also investigated the degree of resilience among these species in terms of certain important morphophysiological and biochemical parameters under N stress. Comparison of the genomic sequences along with their promoter region revealed that both GS2 and Fd-GOGAT genes were located on chromosome 2 and were comprised of 13 and 33 exons respectively. A limited sequence divergence at cDNA and amino acid levels was observed among the genome species, but the divergence was significantly higher in the promoter region. Both these genes were present in three copies in the bread wheat, two copies in the durum wheat, and a single copy in their diploid progenitors. Differential gene expression among the five genome species under N stress suggested major differences in gene regulation due to the difference in cis -elements. Enzyme activity did not correlate with the gene expression level probably due to post-transcriptional and post-translational modification of the enzymes. There was neither correlation between the GS2 and Fd-GOGAT activity in any species. All growth parameters, except root length, decreased or remain unchanged with different degrees of plasticity in the genotypes under N stress and correlated with reduced Fd-GOGAT activity, which supply the primary assimilate glutamate. GS2/Fd-GOGAT enzyme activity along with total N accumulation, protein, chlorophyll, and carotenoid content in shoot were found responsive to the N stress through combined PCA analysis. Our study confirmed the conserved nature of GS2 and Fd-GOGAT enzymes at the CDS and protein level; however, their expression and subsequent effects were different in cultivated wheat and their progenitors.

中文翻译：

---

N胁迫下栽培小麦及其祖代GS2和Fd-GOGAT基因的比较分析

多倍化在栽培小麦（六倍体和四倍体）从其二倍体祖先的发生中起重要作用。因此，多倍化过程中的进化导致了今天的六倍体面包小麦。GS2 和 Fd-GOGAT 酶是参与植物原生氮 (N) 同化的核心成分。在本研究中，我们旨在从分子水平分析这两个重要基因，以找出从古代二倍体祖先到现代六倍体面包小麦的进化过程中发生的变异程度。此外，我们研究了它们的基因表达模式并测定了 N 胁迫下的两种酶。我们还根据氮胁迫下某些重要的形态生理学和生化参数研究了这些物种的恢复力程度。基因组序列及其启动子区域的比较显示 GS2 和 Fd-GOGAT 基因都位于 2 号染色体上，分别由 13 个和 33 个外显子组成。在基因组物种中观察到 cDNA 和氨基酸水平的有限序列差异，但在启动子区域中差异显着更高。这两个基因在面包小麦中以三个拷贝存在，在硬粒小麦中存在两个拷贝，在其二倍体祖先中存在一个拷贝。在氮胁迫下，五个基因组物种之间的差异基因表达表明由于顺式元件的差异，基因调控存在重大差异。酶活性与基因表达水平无关，可能是由于酶的转录后和翻译后修饰。在任何物种中，GS2 和 Fd-GOGAT 活性之间都没有相关性。除根长外，所有生长参数都降低或保持不变，基因型在 N 胁迫下具有不同程度的可塑性，并与 Fd-GOGAT 活性降低相关，后者提供初级同化物谷氨酸。通过联合 PCA 分析，发现 GS2/Fd-GOGAT 酶活性以及总氮积累、蛋白质、叶绿素和类胡萝卜素含量对氮胁迫有响应。我们的研究证实了 GS2 和 Fd-GOGAT 酶在 CDS 和蛋白质水平上的保守性；然而，它们在栽培小麦及其祖先中的表达和随后的影响是不同的。在 N 胁迫下，基因型的可塑性降低或保持不变，并与 Fd-GOGAT 活性降低相关，后者提供初级同化谷氨酸。通过联合 PCA 分析，发现 GS2/Fd-GOGAT 酶活性以及总氮积累、蛋白质、叶绿素和类胡萝卜素含量对氮胁迫有响应。我们的研究证实了 GS2 和 Fd-GOGAT 酶在 CDS 和蛋白质水平上的保守性；然而，它们在栽培小麦及其祖先中的表达和随后的影响是不同的。在 N 胁迫下，基因型的可塑性降低或保持不变，并与 Fd-GOGAT 活性降低相关，后者提供初级同化谷氨酸。通过联合 PCA 分析，发现 GS2/Fd-GOGAT 酶活性以及总氮积累、蛋白质、叶绿素和类胡萝卜素含量对氮胁迫有响应。我们的研究证实了 GS2 和 Fd-GOGAT 酶在 CDS 和蛋白质水平上的保守性；然而，它们在栽培小麦及其祖先中的表达和随后的影响是不同的。通过联合 PCA 分析，发现茎中的和类胡萝卜素含量对 N 胁迫有响应。我们的研究证实了 GS2 和 Fd-GOGAT 酶在 CDS 和蛋白质水平上的保守性；然而，它们在栽培小麦及其祖先中的表达和随后的影响是不同的。通过联合 PCA 分析，发现茎中的和类胡萝卜素含量对 N 胁迫有响应。我们的研究证实了 GS2 和 Fd-GOGAT 酶在 CDS 和蛋白质水平上的保守性；然而，它们在栽培小麦及其祖先中的表达和随后的影响是不同的。