抄録
The plant hormone ABA induces rapid stomatal closure and regulates gene expression to orchestrate adaptive response to drought stress. In Arabidopsis thaliana, genetic evidences have revealed that Protein Phosphatase 2C (PP2C) and Snf1-Related Kinases 2 (SnRK2) including OST1 play prominent roles in ABA signaling.
Starting with a protein phosphatase substrate profiling strategy, we have identified the activation loop of the ABA-activated SnRK2 kinase OST1 as a substrate of the PP2Cs HAB1, ABI1 and ABI2 involved in ABA signaling. Together with the recent studies on the ABA receptors of the PYL/RCAR protein family, our results indicate that SnRK2 kinases are activated very early in ABA signaling through the inhibition of PP2Cs by the PYL/RCAR-ABA complex.
To identify downstream elements of ABA signaling, we performed a bioinformatic screen using the substrate preferences of the OST1 kinase. This screen revealed several putative OST1 substrates including the NADPH oxidase AtRBOHF and transcription factors of the ABF/AREB family.
Together, our results suggest a relatively straightforward architecture of ABA signaling to regulate stomatal closure and gene expression in plants.
