ABA induces a 14-3-3 protein binding to a 61 kDa protein in phosphorylation-dependent manner in Vicia guard cells

Abstract

Protein phosphorylation and dephosphorylation plays an important role during ABA-induced stomatal closure, however, little is known about the signaling in biochemical levels. We found that ABA induced the binding of a 14-3-3 protein to a cytosolic 61 kDa protein in Vicia guard cell protoplasts. The 14-3-3 binding reached the maximum at 1 μM ABA within 3 min, and occurred in vivo. This reaction neither required H₂O₂ nor extracellular Ca²⁺. We showed that this 14-3-3 binding to 61 kDa protein depended on its phosphorylation. Autophosphorylation of 48 kDa AAPK had similar properties to phosphorylation of the 61 kDa protein such as time course in response to ABA and sensitivity to a protein kinase inhibitor K-252a. Furthermore, ABA-activated AAPK phosphorylated the 61 kDa protein in vitro. We conclude that the 61 kDa protein may act as a substrate of AAPK in early ABA signaling pathway in guard cells.