The B'zeta subunit of protein phosphatase 2A negatively regulates ethylene signaling in Arabidopsis

Ethylene is a major plant hormone that regulates plant growth, development, and defense responses to biotic and abiotic stresses. The major pieces of the ethylene signaling pathway have been put together, although several details still need to be elucidated. For instance, the phosphorylation and dephosphorylation processes controlling the ethylene responses are poorly understood and need to be further explored. The type 2A protein phosphatase (PP2A) was suggested to play an important role in the regulation of ethylene biosynthesis, where the A1 subunit of PP2A was shown to be involved in the regulation of the rate-limiting enzyme of the ethylene biosynthetic pathway. However, whether other subunits of PP2A play roles in the ethylene signal transduction pathway is yet to be answered. In this study, we demonstrate that a B subunit, PP2A-B'zeta, positively regulates plant germination and seedling development, as a pp2a-b'zeta mutant is very sensitive to ethylene treatment. Furthermore, PP2A-B'zeta interacts with and stabilizes the kinase CTR1 (Constitutive Triple Response 1), a key enzyme in the ethylene signal transduction pathway, and like CTR1, PP2A-B'zeta negatively regulates ethylene signaling in plants.