Glutamine synthetase GhGLN1.5 regulates arbuscular mycorrhizal symbiosis and Verticillium wilt resistance in cotton by modulating inorganic nitrogen assimilation.

Arbuscular mycorrhizal (AM) fungi play a crucial role in the nitrogen uptake and Verticillium wilt resistance of cotton. The absorbed inorganic nitrogen is converted into organic nitrogen through nitrogen assimilation mediated by glutamine synthetase (GS). However, the role of GS in AM symbiosis and Verticillium wilt resistance remains unclear. We identified an AM fungus-induced GS gene, GhGLN1.5, which participated in AM symbiosis. Both in vivo and in vitro analyses demonstrated that GhGLN1.5 exhibits catalytic activity of GS. The knockdown of GhGLN1.5 resulted in a reduction of AM colonization, nitrogen uptake capacity, and AM symbiosis-dependent resistance to Verticillium wilt. Heterologous expression of GhGLN1.5 enhanced AM symbiosis, increased GS activity, and promoted plant growth. The knockout of GhGLN1.5 in cotton inhibited AM symbiosis. Furthermore, we identified an AM fungus-induced ethylene response factor gene GhWRI3 through yeast one-hybrid library screening and found that GhWRI3 activates the expression of GhGLN1.5 via AW-box element. These findings provide valuable insights into the molecular mechanisms of GhGLN1.5 expression in AM symbiosis, nitrogen assimilation, and Verticillium wilt resistance in cotton, suggesting potential strategies for regulating AM symbiosis in cotton through the WRI3-GLN1.5 module.