Igarashi D, Ishida S, Fukazawa J, Takahashi Y
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan.
Plant Cell. 2001 Nov;13(11):2483-97. doi: 10.1105/tpc.010188.
Gibberellins (GAs) are essential regulators of many aspects of plant development, including stem elongation, seed germination, and flowering. RSG is a transcriptional activator with a basic leucine zipper domain that regulates endogenous amounts of GAs through the control of a GA biosynthetic enzyme. The ubiquitous expression of RSG in plant organs suggests an involvement of post-transcriptional and/or post-translational modifications of the transcription factor. Here, we identify the 14-3-3 signaling proteins as RSG binding partners. The mutant version of RSG that could not bind to 14-3-3 proteins exhibited a higher transcriptional activity than did wild-type RSG. Consistent with this observation, the mutant RSG that could not bind to 14-3-3 proteins was localized predominantly in the nucleus, whereas wild-type RSG was distributed throughout the cell. Using the nuclear export inhibitor leptomycin B, we also showed that RSG, apparently statically localized in the cytoplasm, is capable of shuttling in and out of the nucleus. These results suggest that 14-3-3 proteins negatively modulate RSG, which is involved in the regulation of endogenous amounts of GAs, by controlling its intracellular localization.
赤霉素（GAs）是植物发育诸多方面的重要调节因子，包括茎的伸长、种子萌发和开花。RSG是一种具有碱性亮氨酸拉链结构域的转录激活因子，它通过控制一种GA生物合成酶来调节GA的内源性含量。RSG在植物器官中的普遍表达表明转录因子存在转录后和/或翻译后修饰。在此，我们鉴定出14-3-3信号蛋白为RSG的结合伙伴。不能与14-3-3蛋白结合的RSG突变体比野生型RSG表现出更高的转录活性。与这一观察结果一致，不能与14-3-3蛋白结合的突变体RSG主要定位于细胞核，而野生型RSG则分布于整个细胞。使用核输出抑制剂莱普霉素B，我们还表明，显然静态定位于细胞质中的RSG能够穿梭进出细胞核。这些结果表明，14-3-3蛋白通过控制RSG的细胞内定位对其进行负调控，而RSG参与了GA内源性含量的调节。
