title: A signaling pathway linking nitric oxide production to heterotrimeric G protein and hydrogen peroxide regulates extracellular calmodulin induction of stomatal closure in Arabidopsis.
abstract: Extracellular calmodulin (ExtCaM) regulates stomatal movement by eliciting a cascade of intracellular signaling events including heterotrimeric G protein, hydrogen peroxide (H(2)O(2)), and Ca(2+). However, the ExtCaM-mediated guard cell signaling pathway remains poorly understood. In this report, we show that Arabidopsis (Arabidopsis thaliana) NITRIC OXIDE ASSOCIATED1 (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 Galpha-subunit of heterotrimeric G protein. The ExtCaM-dependent NO accumulation was nullified in gpa1 knockout mutants but enhanced by overexpression of a constitutively active form of GPA1 (cGalpha). In addition, cGalpha Atnoa1 and gpa1-2 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 H(2)O(2). Reduced H(2)O(2) levels in guard cells blocked the stomatal response of cGalpha lines, whereas exogenously applied H(2)O(2) rescued the defect in ExtCaM-mediated stomatal closure in gpa1 mutants. Moreover, the atrbohD/F mutant, which lacks the NADPH oxidase activity in guard cells, had impaired NO generation in response to ExtCaM, and H(2)O(2)-induced stomatal closure and NO accumulation were greatly impaired in Atnoa1. These findings have established a signaling pathway leading to ExtCaM-induced stomatal closure, which involves GPA1-dependent activation of H(2)O(2) production and subsequent AtNOA1-dependent NO accumulation.
authors.affiliation: Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Science, Hebei Normal University, Shijiazhuang 050016, China.
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Li
authors.forename: Yin-Qian
authors.initials: YQ
authors.lastname: Liu
authors.forename: Pin
authors.initials: P
authors.lastname: Lü
authors.forename: Hai-Fei
authors.initials: HF
authors.lastname: Lin
authors.forename: Yang
authors.initials: Y
authors.lastname: Bai
authors.forename: Xue-Chen
authors.initials: XC
authors.lastname: Wang
authors.forename: Yu-Ling
authors.initials: YL
authors.lastname: Chen