A Signaling Pathway Linking Nitric Oxide Production to Heterotrimeric G Protein and Hydrogen Peroxide Regulates Extracellular Calmodulin Induction of Stomatal Closure in Arabidopsis

• Published in: Plant physiology (Bethesda) 2009-05, Vol.150 (1), p.114-124
• Main Authors: Li, Jian-Hua, Liu, Yin-Qian, Lü, Pin, Lin, Hai-Fei, Bai, Yang, Wang, Xue-Chen, Chen, Yu-Ling
• Format: Article
• Language: English
• Subjects: Arabidopsis - cytology; Arabidopsis - drug effects; Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis Proteins - physiology; Biological and medical sciences; Calcium; Calmodulin - pharmacology; Cell Biology and Signal Transduction; Cell lines; Fluorescence; Fundamental and applied biological sciences. Psychology; Gene expression regulation; GTP-Binding Protein alpha Subunits - metabolism; Guard cells; Hydrogen Peroxide - metabolism; Models, Biological; Nitric Oxide - biosynthesis; Nitric Oxide Synthase - genetics; Nitric Oxide Synthase - metabolism; Nitric Oxide Synthase - physiology; Oxides; Physiological regulation; Plant cells; Plant physiology and development; Plant Stomata - drug effects; Plant Stomata - physiology; Plants; Signal Transduction; Stomatal movement
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.109.137067

Extracellular calmodulin (ExtCaM) regulates stomatal movement by eliciting a cascade of intracellular signaling events including heterotrimeric G protein, hydrogen peroxide (H₂O₂), and Ca²⁺. However, the ExtCaM-mediated guard cell signaling pathway remains poorly understood. In this report, we show that Arabidopsis (Arabidopsis thaliana) NITRIC OXIDE ASSOCIATEDl (AtNOA1)-dependent nitric oxide (NO) accumulation plays a crucial role in ExtCaM-induced stomatal closure. ExtCaM triggered a significant increase in NO levels associated with stomatal closure in the wild type, but both effects were abolished in the Atnoa1 mutant. Furthermore, we found that ExtCaM-mediated NO generation is regulated by GPA1, the Ga-subunit of heterotrimeric G protein. The ExtCaM-dependent NO accumulation was nullified in gpa1 knockout mutants but enhanced by overexpression of a consti tu tively active form of GPA1 (cGα). In addition, cGα Atnoa1 and gpal-2 Atnoa1 double mutants exhibited a similar response as did Atnoa1. The defect in gpa1 was rescued by overexpression of Atnoa1. Finally, we demonstrated that G protein activation of NO production depends on H₂O₂ . Reduced H₂O₂ levels in guard cells blocked the stomatal response of cGα lines, whereas exogenously applied H₂O₂ rescued the defect in ExtCaM-mediated stomatal closure in gpal mutants. Moreover, the atrbohD/F mutant, which lacks the NADPH oxidase activity in guard cells, had impaired NO generation in response to ExtCaM, and H₂O₂ -induced stomatal closure and NO accumulation were greatly impaired in Atnoa1. These findings have established a signaling pathway leading to ExtCaM-induced stoma tal closure, which involves GPA1-dependent activation of H₂O₂ production and subsequent AtNOA1-dependent NO accumulation.