Rice GDP dissociation inhibitor 3 inhibits OsMAPK2 activity through physical interaction

► OsGDI3 is a Rab-specific regulator and OsGDI3 interacts with OsMAPK2. ► OsGDI3 inhibits the autophosphorylation activity of OsMAPK2. ► OsGDI3 reduces kinase activity of plant MAPKs. ► OsGDI3 does not have dephosphorylation activity. ► SCR regions in OsGDI3 are necessary to the inhibition of OsMAPK2 activity and physical interaction with OsMAPK2. GDP dissociation inhibitor (GDI) plays an essential role in regulating the state of bound nucleotides and subcellular localizations of Rab proteins. In our previous study, we showed that OsGDI3 facilitates the recycling of OsRab11 with a help of OsGAP1. In this study, we show that OsGDI3 complement the yeast sec19-1 mutant, a temperature-sensitive allele of the yeast GDI gene, suggesting that OsGDI3 is a functional ortholog of yeast GDI. To obtain further knowledge on the function of OsGDI3, candidate OsGDI3-interacting proteins were identified by yeast two-hybrid screens. OsMAPK2 is one of OsGDI3 interacting proteins from yeast two-hybrid screens and subject to further analysis. A kinase assay showed that the autophosphorylation activity of OsMAPK2 is inhibited by OsGDI3 in vitro. In addition, ectopic expressions of OsGDI3-in Arabidopsis cause reductions at the level of phosphorylated AtMPK in phosphorylation activity. Taken together, OsGDI3 functions as a negative regulator of OsMAPK2 through modulating its kinase activity.