OsCPL3 is involved in brassinosteroid signaling by regulating OsGSK2 stability

Glycogen synthase kinase 3(GSK3)proteins play key roles in brassinosteroid(BR)signaling during plant growth and development by phosphorylating various substrates.However,how GSK3 protein stability and activity are themselves modulated is not well understood.Here,we demonstrate in vitro and in vivo that C-TERMINAL DOMAIN PHOSPHATASELIKE 3(Os CPL3),a member of the RNA Pol II CTD phosphatase-like family,physically interacts with Os GSK2 in rice(Oryza sativa).Os CPL3 expression was widely detected in various tissues and organs including roots,leaves and lamina joints,and was induced by exogenous BR treatment.Os CPL3 localized to the nucleus,where it dephosphorylated Os GSK2 at the Ser-222 and Thr-284 residues to modulate its protein turnover and kinase activity,in turn affecting the degradation of BRASSINAZOLERESISTANT 1(BZR1)and BR signaling.Loss of Os CPL3 function resulted in higher Os GSK2 abundance and lower Os BZR1 levels,leading to decreased BR responsiveness and alterations in plant morphology including semi-dwarfism,leaf erectness and grain size,which are of fundamental importance to crop productivity.These results reveal a previously unrecognized role for Os CPL3 and add another layer of complexity to the tightly controlled BR signaling pathway in plants.