FIGURE 5.

Proposed model of ROS inhibition by coronatine in the context of ABA signaling. Coronatine inhibits stomatal closure induced by ABA and flg22 through inhibition of ROS synthesis by NADPH oxidases AtRBOHD and AtRBOHF. This toxin does not affect promotion of stomatal closure by SA, which induces ROS synthesis mediated by peroxidases. In atrbohd, mpk3, mpk6, npr1-3, and lecrkVI-2.1 mutants the sensitivity to ABA is not affected by coronatine or DPI. This might be due to negative regulation by ROS of other ABA signaling components, which would be upregulated in these mutants. Thus in these mutants ABA is able to close stomata in the absence of ROS signaling.