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

RSG （Repression of Shoot Growth）是一种bZIP转录因子，通过调节植物激素赤霉素（gibberellin， GA）生物合成酶的表达来决定植物茎的伸长生长。此外，RSG还通过GA反馈调控激活了另一种GA生物合成酶的表达。在这种情况下，来自内部发育线索和外部环境环境的信号被认为整合在RSG上，然后转化为其转录活性，以维持植物中GA的稳态，以实现适当的伸长生长。为了从分子角度全面了解GA的伸长生长，研究了调控RSG活性的机制。内源GA水平升高诱导RSG的S114磷酸化，这是抑制RSG.2负调控因子14-3-3的必要条件。RSG.3将RSG与14-3-3之间的复合体从细胞核中排除，导致了一个GA生物合成酶的转录被RSG.3打断。RSG的S114被钙依赖性蛋白激酶NtCDPK1.4特异性磷酸化。内源性GA水平的升高诱导NtCDPK1磷酸化，增强了RSG与NtCDPK1之间的亲和力，提示RSG与NtCDPK1在磷酸化反应中可以超越激酶与底物之间的短暂结合。在本研究中，GA信号在反馈调节中被探测通过NtCDPK1传输到RSG。NtCDPK1磷酸化RSG的S114，导致RSG与14-3-3之间形成复合物，使复合物从细胞核中排除，抑制RSG对GA生物合成酶的转录激活。

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.