Abscisic acid (ABA) is a crucial plant hormone involved in various physiological processes, including seed dormancy, root development, leaf senescence, and drought tolerance. Its role in helping plants respond to environmental stress makes it a key player in survival under adverse conditions.
Recently, a research team from the Shanghai Institute of Life Sciences, Chinese Academy of Sciences, in collaboration with Purdue University, uncovered a negative regulatory mechanism in ABA signaling. This groundbreaking study was published in the prestigious journal *Proceedings of the National Academy of Sciences* (PNAS). The lead author of the paper is Professor Jian-Kang Zhu from the Center for Plant Stress Biology at the Chinese Academy of Sciences.
When plants face drought stress, ABA accumulates and activates the protein kinase OST1/SnRK2.6. This activation leads to the phosphorylation of numerous proteins in guard cells, triggering stomatal closure and reducing water loss through transpiration. However, the recent study reveals that ABA also induces the production of nitric oxide (NO) in guard cells. NO causes S-nitrosylation of a specific cysteine residue near the catalytic site of SnRK2.6, which inhibits its kinase activity.
The research further shows that when the enzyme GSNO reductase is dysfunctional, it results in excessive accumulation of GSNO in guard cells. This leads to prolonged S-nitrosylation of SnRK2.6, making the plant less responsive to ABA signals, thus impairing stomatal regulation.
Interestingly, the study also highlights that similar cysteine residues exist in several protein kinases found in yeast and humans. These residues can also undergo S-nitrosylation, suggesting that this regulatory mechanism may be evolutionarily conserved across species.
This discovery not only deepens our understanding of how ABA signaling is regulated but also opens new avenues for improving crop resilience to environmental stresses, which is increasingly important in the context of climate change.
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