Edited by Maarten J. Chrispeels, University of California, San Diego, La Jolla, CA, and approved July 14, 2017 (received for review March 27, 2017)
Guard cells play a crucial role in controlling transpiration and the plant water status. Here, we show that the Arabidopsis plasma membrane aquaporin PIP2;1 is involved in stomatal closure triggered by abscisic acid (ABA) or the pathogen-associated molecular pattern flg22. The use of a genetic probe for hydrogen peroxide (H2O2) revealed that PIP2;1 is also required for intracellular accumulation of H2O2 after flg22 or ABA treatments. Our data lead to a model whereby flg22 and ABA activate PIP2;1 through phosphorylation at a conserved site to facilitate transport of both water and H2O2 and promote stomatal closure. This study fills a gap in our understanding of stomatal regulation and suggests a general signaling role of aquaporin in contexts involving H2O2.
Stomatal movements are crucial for the control of plant water status and protection against pathogens. Assays on epidermal peels revealed that, similar to abscisic acid (ABA), pathogen-associated molecular pattern (PAMP) flg22 requires the AtPIP2;1 aquaporin to induce stomatal closure. Flg22 also induced an increase in osmotic water permeability (Pf) of guard cell protoplasts through activation of AtPIP2;1. The use of HyPer, a genetic probe for intracellular hydrogen peroxide (H2O2), revealed that both ABA and flg22 triggered an accumulation of H2O2 in wild-type but not pip2;1 guard cells. Pretreatment of guard cells with flg22 or ABA facilitated the influx of exogenous H2O2. Brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1) and open stomata 1 (OST1)/Snf1-related protein kinase 2.6 (SnRK2.6) were both necessary to flg22-induced Pf and both phosphorylated AtPIP2;1 on Ser121 in vitro. Accumulation of H2O2 and stomatal closure as induced by flg22 was restored in pip2;1 guard cells by a phosphomimetic form (Ser121Asp) but not by a phosphodeficient form (Ser121Ala) of AtPIP2;1. We propose a mechanism whereby phosphorylation of AtPIP2;1 Ser121 by BAK1 and/or OST1 is triggered in response to flg22 to activate its water and H2O2 transport activities. This work establishes a signaling role of plasma membrane aquaporins in guard cells and potentially in other cellular context involving H2O2 signaling.
↵1Present address: UMR Plant Diversity Adaptation and Development - Research Unit (DIADE), Institut de Recherche pour le Développement/Université de Montpellier, F-34394 Montpellier Cedex 5, France.
Author contributions: O.R., C.M., and L.V. designed research; O.R., G.R., and L.V. performed research; O.R., A.G., Y.S., N.L., and L.V. contributed new reagents/analytic tools; O.R., G.R., and L.V. analyzed data; and O.R., C.M., and L.V. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1704754114/-/DCSupplemental.
