Identification and characterization of the glutamine synthetase gene family in oat (Avena sativa L.) and the role of AsGS2-2C under drought stress

Drought is a critical limiting factor for crop yield, posing a substantial threat to global food security and negatively influencing plant growth and development. As a crop used as both a grain and forage, the yield of oat <i>(Avena sativa)</i> is significantly affected by drought. Glutamine synthetase <i>(GS)</i> is a crucial enzyme in plant nitrogen metabolism and plays an essential role in nitrogen utilization, growth regulation, and yield formation. We used bioinformatics analysis to identify the <i>GS</i> gene family in oats, and employed molecular biology, genetics and plant physiology methods to investigate the drought-resistant function of <i>AsGS2-2C</i>. In this study, 11 oat <i>AsGS</i> genes were identified, and the gene family and expression patterns were analyzed. Our findings revealed that a majority of <i>AsGS</i> genes were upregulated under drought and salt stress, whereas they were downregulated in response to cold stress and abscisic acid treatment. Cloning and functional analysis of the <i>AsGS2-2C</i> gene revealed that transgenic tobacco overexpressing <i>AsGS2-2C</i> presented increased tolerance to drought stress in phenotype. Physiological analyses revealed an increase in antioxidant enzyme activities and a reduction in membrane damage in AsGS2-2C-overexpressing plants. Under drought conditions, the expression of stress-responsive genes (<i>Cu/Zn-SOD, MnSOD, CBL1, GR1, GAPC, Gln1-5</i>, and <i>BI-1</i>) was significantly elevated in <i>AsGS2-2C</i> transgenic tobacco. Interestingly, <i>ACR11, GLU, ERD10B, Hxk3</i> and <i>Ltp1</i> exhibited initial upregulation followed by subsequent downregulation. These findings provide valuable insights into the molecular mechanisms underlying drought tolerance mediated by <i>AsGS2-2C</i> in oat, offering potential targets for crop improvement against drought.