Analysis of regulation of a transcription factor RSG contcolling endogenous level of Gibberellins

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RSG (Repression of Shoot Growth) is a bZIP transcriptional factor which determines elongation growth of stem of plants by regulating expressions of a biosynthetic enzyme for a plant hormone, gibberellin(GA). Besides, it was demonstrated that RSG activates expression of another GA biosynthetic enzyme upon GA feedback regulation. In this context, signals from interior developmental cues and exterior environmental milieus are thought to be integrated on RSG and then converted into its transcriptional activity to maintain GA homeostasis in planta for appropriate elongation growth.For comprehensive understanding of elongation growth by GA in molecular terms, the mechanism by which activity of RSG is regulated was studied.1. The elevation of endogenous level of GA induced phosphorylation of S114 of RSG which is essential for biding with 14-3-3, a negative regulator of RSG.2. The complex between RSG and 14-3-3 was excluded from nucleus resulting shot off of transcription of a GA biosynthetic enzyme by RSG.3. S114 of RSG was specifically phosphorylated by a calcium-dependent protein kinase, NtCDPK1.4. The elevation of endogenous level of GA induced phosphorylation of NtCDPK1 and potentiated the affinity between RSG and NtCDPK1, suggesting RSG and NtCDPK1 could interact beyond the transient association between a kinase and a substrate in the reaction of phosphorylation.In this study, GA signal was probed to be transmitted to RSG via NtCDPK1 in the feedback regulation. The phosphorylation of S114 of RSG by NtCDPK1 leads to the formation of complex between RSG and 14-3-3 resulting the exclusion of the complex from nucleus and repression of transcriptional activation of the GA biosynthetic enzyme by RSG.