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

PABLO S. TORRES; ADRIÁN A. VOJNOV; LAILA TOUM; MARÍA P. BENAVÍDES; SUSANA M. GALLEGO; GUSTAVO E. GUDESBLAT

Frontiers in Plant Science

Frontiers

Año: 2016

1664-462X

Microbes trigger stomatal closure through microbe-associated molecular patterns(MAMPs). The bacterial pathogen Pseudomonas syringae pv. tomato (Pst) synthesizesthe polyketide toxin coronatine, which inhibits stomatal closure by MAMPs and thehormone abscisic acid (ABA). The mechanism by which coronatine, a jasmonic acidisoleucineanalog, achieves this effect is not completely clear. Reactive oxygen species(ROS) are essential second messengers in stomatal immunity, therefore we investigatedthe possible effect of coronatine on their production. We found that coronatineinhibits NADPH oxidase-dependent ROS production induced by ABA, and by theflagellin-derived peptide flg22. This toxin also inhibited NADPH oxidase-dependentstomatal closure induced by darkness, however, it failed to prevent stomatal closure byexogenously applied H2O2 or by salicylic acid, which induces ROS production throughperoxidases. Contrary to what was observed on stomata, coronatine did not affect theoxidative burst induced by flg22 in leaf disks. Additionally, we observed that in NADPHoxidase mutants atrbohd and atrbohd/f, as well as in guard cell ABA responsive butflg22 insensitive mutants mpk3, mpk6, npr1-3, and lecrk-VI.2-1, the inhibition of ABAstomatal responses by both coronatine and the NADPH oxidase inhibitor diphenyleneiodonium was markedly reduced. Interestingly, coronatine still impaired ABA-inducedROS synthesis in mpk3, mpk6, npr1-3, and lecrk-VI.2-1, suggesting a possible feedbackregulation of ROS on other guard cell ABA signaling elements in these mutants.Altogether our results show that inhibition of NADPH oxidase-dependent ROS synthesisin guard cells plays an important role during endophytic colonization by Pst throughstomata.