Nitrate reductase-mediated nitric oxide synthesis in shaping stress resilience in plants

Nitrate reductase (NR), a key enzyme in nitrogen metabolism, catalyses reductive nitric oxide (NO) production in plants. However, the functional roles of NR and NR-mediated NO evolution in shaping stress adaptation in plants remain largely elusive. In recent years, significant progress has been made in NR research, leading to the identification of (i) specific physiological conditions under which NR-mediated NO production takes place, (ii) signaling proteins associated with the activation of NR, and (iii) various post-translational modifications that affect the activity and stability of NR. Emerging evidence has also revealed dynamic interplay among NO, classical phytohormones, and emerging plant growth regulators, which collectively modulate defense responses in plants. Notably, NR-dependent NO plays a pivotal role in maintaining nutrient uptake and reactive oxygen species (ROS) homeostasis under various stress conditions. It also contributes to root development, stomatal closure, secondary metabolite biosynthesis, defense gene expression, and the hypersensitive response, depending on the specific type of stress to facilitate stress mitigation. The present review provides recent advancements in the regulation of NR activity, the specific cellular signals involved, and the impact of classical phytohormones and emerging plant growth regulators on NO production to broaden our understanding of the multifaceted role of NR and provide insights into potential strategies for improving crop resilience.