Arabidopsis 3-Ketoacyl-CoA Thiolase-2 (KAT2), an Enzyme of Fatty Acid β-Oxidation, is Involved in ABA Signal Transduction

The phytohormone ABA plays an important role in plant development and adaptation to diverse environmental stresses. Many of the components involved in ABA signaling remain to be discovered, and knowledge of these is needed to understand fully the highly complex ABA signaling network. Here, we report that an enzyme catalyzing beta-oxidation of fatty acids, 3-ketoacyl-CoA thiolase-2 (KAT2/PED1/PKT3) (EC 2.3.1.16), is involved in ABA signaling. We provide genetic evidence that KAT2 positively regulates ABA signaling in all the major ABA responses, including ABA-induced inhibition of seed germination and post-germination growth arrest, and ABA-induced stomatal closure and stomatal opening inhibition in Arabidopsis thaliana. KAT2 was shown to be important for reactive oxygen species (ROS) production in response to ABA, suggesting that KAT2 regulates ABA signaling at least partly through modulating ROS homeostasis in plant cells. Additionally, we provide data suggesting that KAT2 may function downstream of an important WRKY transcription repressor WRKY40, which may link KAT2 with the ABA receptor ABAR/CHLH-mediated signaling.