The Arabidopsis kinase-associated protein phosphatase KAPP, interacting with protein kinases SnRK2.2/2.3/2.6, negatively regulates abscisic acid signaling.

KEY MESSAGE: The kinase-associated protein phosphatase, KAPP, is negatively involved in abscisic acid (ABA) signaling. KAPP interacts physically with SnRK2.2, SnRK2.3 and SnRK2.6, and functionally acts upstream of SnRK2.2 and SnRK2.3. The kinase-associated protein phosphatase (KAPP) has been reported to be involved in the regulation of many developmental and signaling events, but it remains unknown whether KAPP is involved in ABA signaling. Here, we report that KAPP is negatively involved in ABA-mediated seed germination and early seedling growth in Arabidopsis thaliana. The two loss-of-function mutants of KAPP, kapp-1 and kapp-2, exhibit increased ABA sensitivity in ABA-induced seed germination inhibition and post-germination growth arrest. The three closely-related protein kinase, (SNF1)-related protein kinase SnRK2.2, SnRK2.3 and SnRK2.6, which play critical roles in ABA signaling, interact and co-localize with KAPP. Genetic evidence showed that the ABA-hypersensitive phenotypes caused by KAPP mutation were suppressed by the double mutation of SnRK2.2 and SnRK2.3, indicating that KAPP functions upstream of SnRK2.2 and SnRK2.3 in ABA signaling. RNA-sequencing analysis revealed that KAPP mutation affects expression of multiple ABA-responsive genes. These results demonstrated that KAPP is negatively involved in plant response to ABA, which help to understand the complicated ABA signaling mechanism.