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

RSG是一种bZIP转录因子，它通过调节植物激素赤霉素(GA)的生物合成酶的表达来决定植物茎的伸长生长。此外，还证明了RSG在GA反馈调控下激活了另一种GA生物合成酶的表达。在这种背景下，来自内部发育线索和外部环境的信号被认为整合在RSG上，然后转化为其转录活性，以维持植物体内GA的动态平衡，以实现适当的伸长生长。为了从分子上全面理解GA对伸长生长的影响，我们研究了RSG活性的调控机制。内源GA水平的升高诱导了RSG S114的磷酸化，这是RSG14-3-3与RSG14-3-3结合所必需的。RSG与14-3-3之间的复合体被RSG.3从细胞核中排除，导致GA生物合成酶的转录。RSG的S114被钙依赖蛋白激酶NtCDPK1.4特异性磷酸化。内源GA水平的升高诱导了NtCDPK1的磷酸化，并增强了RSG与NtCDPK1之间的亲和力，表明RSG和NtCDPK1在磷酸化反应中的相互作用超越了激酶和底物之间的瞬时结合。NtCDPK1将RSG的S114磷酸化，导致RSG与14-3-3形成复合体，导致该复合体被排除在细胞核之外，抑制了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.