UC San Diego

The plant hormone abscisic acid (ABA) controls the water status of plants by regulating many physiological processes including seed germination, root growth and stomatal movements. However, the molecular mechanisms of ABA signaling have yet to be fully understood. Here, the involvement of Type 2A protein phosphatases (PP2As) in ABA signaling has been studied. To functionally characterize Arabidopsis PP2As, subcellular localization and protein- protein-interaction analyses of PP2As were performed. These analyses revealed that all PP2AAs and PP2ACs are localized in the cytoplasm and the nucleus and can form complexes among each other in the cytoplasm, however with varying interaction strength. Phenotypical assays with pp2a double mutant combinations revealed an ABA hyposensitivity during seed germination, but ABA hypersensitivity during root growth and no altered response during ABA-induced stomatal closure. These ABA responses could be linked to the physical interaction of PP2As with the protein kinase OST1, which is part of the core ABA signaling pathway