Poster: Regulation of gene expression

Abs # 736: Involvement of 14-3-3 binding in the functional regulation of RSG by gibberellins

Presenter:	Ishida, Sarahmi , ishida@biol.s.u-tokyo.ac.jp
Authors	Ishida, Sarahmi  (A)   Yuasa, Takashi  (A)   Fukazawa, Jutarou  (B)   Takahashi, Youshuke  (B)
Affiliations:	(A): University of Tokyo (B): Hiroshima University

RSG is a transcriptional activator with a basic leucine zipper domain that regulates endogenous amounts of gibberellins (GAs) by the control of a GA biosynthetic enzyme, ent-kaurene oxidase. The 14-3-3 signaling proteins specifically interact with RSG and suppress it by sequestering it in the cytoplasm. Here, we showed that RSG phosphorylation on Ser-114 is important for 14-3-3 protein binding. We found that GA amounts regulate the function of RSG through 14-3-3 protein binding. RSG translocated into the nucleus in response to a reduction in the level of endogenous GAs. Treatment with GAs could reverse this nuclear accumulation. The GA-induced disappearance of RSG-GFP from the nucleus did not depend on protein degradation. In contrast, the mutant RSG (S114A) that could not bind to 14-3-3 protein continued to be localized predominantly in the nucleus after GA application. Analysis of the mRNA levels of GA biosynthetic genes showed that the feedback regulation of the GA 20-oxidase gene was inhibited in transgenic plants expressing a dominant negative form of RSG. Our results suggest that RSG is negatively modulated by GAs by 14-3-3 protein binding and might be involved in GA homeostasis.