Phosphorylation-Independent binding of 14–3–3 to NtCDPK1 by a new mode

Abstract

14–3–3 proteins play essential roles in diverse cellular processes through the direct binding to target proteins. REPRESSION OF SHOOT GROWTH (RSG) is a tobacco (Nicotiana tabacum) transcription factor that is involved in gibberellin (GA) feedback regulation. The 14–3–3 proteins bind to RSG depending on the RSG phosphorylation of Ser-114 and negatively regulate RSG by sequestering it in the cytoplasm in response to GAs. The Ca2C -dependent protein kinase NtCDPK1 was identified as an RSG kinase that promotes 14–3–3 binding of RSG by phosphorylation of RSG. 14–3– 3 weakly binds to NtCDPK1 by a new mode. The autophosphorylation of NtCDPK1 was necessary for the formation of the binding between NtCDPK1 and 14–3–3 but not for its maintenance. In this study, we showed that 14–3–3 binding to NtCDPK1 does not require the autophosphorylation when RSG was bound to NtCDPK1. These data suggest that 14–3–3 binds to an unphosphorylated motif in NtCDPK1 exposed by a conformational change in NtCDPK1 but not to a phosphate group generated by autophosphorylation of NtCDPK1.