Abscisic acid-induced degradation of Arabidopsis guanine nucleotide exchange factor requires calcium-dependent protein kinases

Significance Arabidopsis RopGEF1 acts as a negative regulator of signal transduction by the plant hormone abscisic acid (ABA). In turn, ABA treatment causes subcellular translocation and degradation of RopGEF1 protein. Interestingly, PP2C protein phosphatases, the core negative regulators of ABA signal transduction, protect RopGEF1 from degradation. This suggests that protein kinases may be involved in RopGEF1 protein removal. We find that calcium-dependent protein kinases (CPKs) including CPK4 phosphorylate RopGEF1. CPK4 promotes RopGEF1 degradation in Arabidopsis . CPK4 also negatively regulates RopGEF1 activities in root hair development. Furthermore, phosphorylation of serine residues at the N terminus of RopGEF1 is important for RopGEF1 degradation. We further discuss possible abiotic stress-triggered repression of plant growth via CPK-mediated removal of RopGEF.