title: Coronatine Inhibits Stomatal Closure through Guard Cell-Specific Inhibition of NADPH Oxidase-Dependent ROS Production.
abstract: Microbes trigger stomatal closure through microbe-associated molecular patterns (MAMPs). The bacterial pathogenPseudomonas syringaepv.tomato(Pst) synthesizes the polyketide toxin coronatine, which inhibits stomatal closure by MAMPs and by the hormone abscisic acid (ABA). The mechanism by which coronatine, a jasmonic acid-isoleucine analog, achieves this effect is not completely clear. Reactive oxygen species (ROS) are essential second messengers in stomatal immunity, therefore we investigated the possible effect of coronatine on their production. We found that coronatine inhibits NADPH oxidase-dependent ROS production induced by ABA, and by the flagellin-derived peptide flg22. This toxin also inhibited NADPH oxidase-dependent stomatal closure induced by darkness, however, it failed to prevent stomatal closure by exogenously applied H2O2or by salicylic acid, which induces ROS production through peroxidases. Contrary to what was observed on stomata, coronatine did not affect the oxidative burst induced by flg22 in leaf disks. Additionally, we observed that in NADPH oxidase mutantsatrbohdandatrbohd/f, as well as in guard cell ABA responsive but flg22 insensitive mutantsmpk3, mpk6, npr1-3, andlecrk-VI.2-1, the inhibition of ABA stomatal responses by both coronatine and the NADPH oxidase inhibitor diphenylene iodonium was markedly reduced. Interestingly, coronatine still impaired ABA-induced ROS synthesis inmpk3, mpk6, npr1-3, andlecrk-VI.2-1, suggesting a possible feedback regulation of ROS on other guard cell ABA signaling elements in these mutants. Altogether our results show that inhibition of NADPH oxidase-dependent ROS synthesis in guard cells plays an important role during endophytic colonization byPstthrough stomata.
authors.affiliation: Instituto de Ciencia y Tecnología Dr. César Milstein, Fundación Pablo Cassará, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina.
authors.forename: Laila
authors.initials: L
authors.lastname: Toum
authors.affiliation: Instituto de Ciencia y Tecnología Dr. César Milstein, Fundación Pablo Cassará, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina.
authors.forename: Pablo S
authors.initials: PS
authors.lastname: Torres
authors.affiliation: Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires Buenos Aires, Argentina.
authors.forename: Susana M
authors.initials: SM
authors.lastname: Gallego
authors.affiliation: Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires Buenos Aires, Argentina.
authors.forename: María P
authors.initials: MP
authors.lastname: Benavídes
authors.affiliation: Instituto de Ciencia y Tecnología Dr. César Milstein, Fundación Pablo Cassará, Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires, Argentina.
authors.forename: Adrián A
authors.initials: AA
authors.lastname: Vojnov
authors.affiliation: Instituto de Ciencia y Tecnología Dr. César Milstein, Fundación Pablo Cassará, Consejo Nacional de Investigaciones Científicas y TécnicasBuenos Aires, Argentina; Instituto de Biodiversidad y Biología Experimental y Aplicada, Departamento de Biodiversidad y Biología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos AiresBuenos Aires, Argentina.
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Gudesblat
keywords: Arabidopsis thaliana; NADPH oxidase; abscisic acid; coronatine; reactive oxygen species; stomata