The Central Role of GSNOR: Decoding Nitric Oxide Signaling for Crop Stress Tolerance.

S-nitrosoglutathione (GSNO) reductase (GSNOR) is a major and conserved enzyme in prokaryotes and eukaryotes. It reduces a stable nitric oxide (NO) reservoir, GSNO, to balance the organisms' redox status through S-nitrosylation. Over the last few decades, much of our understanding of GSNOR's roles in plant biology has been updated. Here, therefore, we review the current knowledge of GSNOR in plant physiology and signaling under abiotic and biotic stresses. We observe that the role of GSNOR in plant abiotic stress is widely studied in both model and crop plants, whereas studies on its role in biotic stress have mainly focused on model plants. Under abiotic stresses, GSNOR plays a pleiotropic role in terms of plant tolerance and sensitivity. The presence or absence of GSNOR activity modulates the endogenous NO pool that balances plant reactive nitrogen species (RNS) and reactive oxygen species (ROS) under stress conditions. Moreover, GSNOR regulates hormonal levels, like ethylene, abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA), in response to abiotic and biotic stress conditions. Although GSNOR is important in plant physiology, its regulation of the redox switch is directly influenced by the extent of S-nitrosylation, where S-nitrosylated proteins generally enhance plant tolerance to abiotic stress but simultaneously suppress plant immunity. We further highlight a new perspective on NO-based nanotechnology in agriculture, focusing on GSNO encapsulated in nanocarriers. This technology improves NO stability and opens new avenues by allowing an evaluation of GSNOR's role for sustainable crop production. Intriguingly, we discuss knowledge gaps, which are crucial to understanding the role of GSNOR in plant stress tolerance. Overall, this review accumulates a comprehensive understanding of the GSNOR enzyme in crop biology, which could aid in harnessing its function to address the impacts of climate change.