Abstract
The phytohormone abscisic acid (ABA) regulates diverse cellular processes including modulation of seed dormancy, seed maturation, stomatal movements, gene expression, and vegetative growth during plant development. Many studies have shown that protein de/phosphorylation is the major mechanism regulating ABA signaling in guard cells. We have identified two MAP kinase genes, MPK9 and MPK12, which are highly and preferentially expressed in guard cells. Our results show that MPK12 is activated by ABA and H2O2. Furthermore, our molecular genetic and cell biological data demonstrate that MPK9 and MPK12 have overlapping functions and act downstream of ROS to positively regulate guard cell ABA signaling. Using a biochemical approach, we show that the ABA-activated OST1 protein kinase physically interacts with and phosphorylates the NADPH oxidase AtrbohF, which is responsible for the production of reactive oxygen species (ROS) in response to ABA in order to mediate ABA signaling in guard cells. Further progress will be also discussed.
