Coronatine inhibits stomatal closure through guard cell-specific inhibition of NADPH oxidase-dependent ROS production

TOUM L; TORRES PS; GALLEGO SM; BENAVIDES MP; VOJNOV AA; GUDESBLAT GE

Frontiers in Plant Science

Frontiers Media

Año: 2016

1664-462X

Microbes trigger stomatal closure through microbe-associated molecular3 patterns (MAMPs). The bacterial pathogen Pseudomonas syringae pv. tomato (Pst)4 synthesizes the polyketide toxin coronatine, which inhibits stomatal closure by MAMPs5 and the hormone abscisic acid (ABA). The mechanism by which coronatine, a jasmonic6 acid-isoleucine analog, achieves this effect is not completely clear. Reactive oxygen7 species (ROS) are essential second messengers in stomatal immunity, therefore we8 investigated the possible effect of coronatine on their production. We found that9 coronatine inhibits NADPH oxidase-dependent ROS production induced by ABA, and10 by the flagellin-derived peptide flg22. This toxin also inhibited NADPH oxidase11dependent stomatal closure induced by darkness, however it failed to prevent stomatal12 closure by exogenously applied H2O2 or by salicylic acid, which induces ROS13 production through peroxidases. Contrary to what was observed on stomata, coronatine14 did not affect the oxidative burst induced by flg22 in leaf discs. Additionally, we15 observed that in NADPH oxidase mutants atrbohd and atrbohd/f, as well as in guard16 cell ABA responsive but flg22 insensitive mutants mpk3, mpk6, npr1-3 and lecrk-VI.2-17 1, the inhibition of ABA stomatal responses by both coronatine and the NADPH18 oxidase inhibitor diphenylene iodonium was markedly reduced. Interestingly,19 coronatine still impaired ABA-induced ROS synthesis in mpk3, mpk6, npr1-3 and lecrk-20 VI.2-1, suggesting a possible feedback regulation of ROS on other guard cell ABA21 signalling elements in these mutants. Altogether our results show that inhibition of22 NADPH oxidase-dependent ROS synthesis in guard cells plays an important role during23 endophytic colonization by Pst through stomata.