FHY1 mediates nuclear import of the light-activated phytochrome A photoreceptor.
FHY1 mediates nuclear import of the light-activated phytochrome A photoreceptor.
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DOI：
10.1371/journal.pgen.1000143
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发表时间：
2008-08-01
期刊：
影响因子：
4.5
通讯作者：
Fankhauser, Christian
中科院分区：
文献类型：
--
作者：
Genoud, Thierry;Schweizer, Fabian;Tscheuschler, Anke;Debrieux, Dimitry;Casal, Jorge J.;Schaefer, Eberhard;Hiltbrunner, Andreas;Fankhauser, Christian
光受体的光敏色素（phy）家族在高等植物的整个生命周期中至关重要。大多数光敏色素反应都需要光诱导的核输入。phyA的核积累依赖于两种相关蛋白，即FHY1（远红光下下胚轴伸长1）和FHL（类FHY1），其中FHY1起主要作用。FHY1和FHL的转录受FHY3（远红光下下胚轴伸长3）和FAR1（远红光反应受损1）这一对相关转录因子的控制，因此它们间接控制phyA的核积累。FHY1和FHL优先与光激活形式的phyA相互作用，但它们使光受体在细胞核中积累的机制仍未解决。对众多FHY1相关蛋白的序列比较表明，只有位于N端的核定位信号（NLS）和位于C端的phyA相互作用结构域是保守的。我们证明FHY1的这两个部分足以实现FHY1的功能。在存在大量无法进入细胞核的FHY1变体时，phyA的核积累受到抑制。此外，当一个NLS序列与phyA融合时，phyA的核积累变得不依赖于光和FHY1，这有力地表明FHY1介导光激活的phyA的核输入。与这一观点一致的是，在表达组成型核定位版本的phyA的幼苗中，FHY1和FHY3在功能上是可有可无的。我们的数据表明，在拟南芥中发现的机制在高等植物中是保守的。此外，这一机制使我们能够提出一个模型来解释为什么phyA需要一种特定的核输入途径。
为了应对环境变化，动物可以寻找庇护所，而固着生长的植物必须适应普遍存在的条件。生长和发育的高度可塑性是植物如何应对变化环境的显著例子。在植物中，光是能量的来源，也是几类光受体所感知的重要信息线索。光敏色素介导的光信号传导研究得特别深入，因为这些光受体控制着植物生命周期的各个方面。光敏色素在黑暗中位于细胞质，在光激活时必须进入细胞核以启动信号转导。人们对这一重要的光调节事件是如何实现的了解甚少。在这里我们描述一种进化上保守的蛋白FHY1（远红光下下胚轴伸长1）的功能。我们证明FHY1在细胞质中与一种光激活的光敏色素相互作用，使复合物能够被运输到细胞核中。有趣的是，如果这种光敏色素能够通过另一种机制进入细胞核，那么FHY1对于幼苗发育就不再是必需的，这表明FHY1的一个主要功能是将一种激活的光敏色素护送到细胞核中。我们的实验表明，在拟南芥中发现的这种机制在开花植物中广泛保守。
The phytochrome (phy) family of photoreceptors is of crucial importance throughout the life cycle of higher plants. Light-induced nuclear import is required for most phytochrome responses. Nuclear accumulation of phyA is dependent on two related proteins called FHY1 (Far-red elongated HYpocotyl 1) and FHL (FHY1 Like), with FHY1 playing the predominant function. The transcription of FHY1 and FHL are controlled by FHY3 (Far-red elongated HYpocotyl 3) and FAR1 (FAr-red impaired Response 1), a related pair of transcription factors, which thus indirectly control phyA nuclear accumulation. FHY1 and FHL preferentially interact with the light-activated form of phyA, but the mechanism by which they enable photoreceptor accumulation in the nucleus remains unsolved. Sequence comparison of numerous FHY1-related proteins indicates that only the NLS located at the N-terminus and the phyA-interaction domain located at the C-terminus are conserved. We demonstrate that these two parts of FHY1 are sufficient for FHY1 function. phyA nuclear accumulation is inhibited in the presence of high levels of FHY1 variants unable to enter the nucleus. Furthermore, nuclear accumulation of phyA becomes light- and FHY1-independent when an NLS sequence is fused to phyA, strongly suggesting that FHY1 mediates nuclear import of light-activated phyA. In accordance with this idea, FHY1 and FHY3 become functionally dispensable in seedlings expressing a constitutively nuclear version of phyA. Our data suggest that the mechanism uncovered in Arabidopsis is conserved in higher plants. Moreover, this mechanism allows us to propose a model explaining why phyA needs a specific nuclear import pathway. In response to changes in the environment, animals can take shelter while the sessile plants must adapt to the prevalent conditions. Great plasticity in growth and development are striking examples of how plants cope with a changing environment. In plants, light is both a source of energy and an essential informational cue perceived by several classes of photoreceptors. Phytochrome-mediated light signaling is particularly well studied, because these photoreceptors control all aspects of the plant life cycle. The phytochromes are cytoplasmic in the dark and must enter the nucleus upon light activation to initiate signal transduction. How this important light-regulated event is achieved is poorly understood. Here we describe the function of an evolutionary conserved protein called FHY1 for Far-red elongated HYpocotyl 1. We demonstrate that FHY1 interacts with a light-activated phytochrome in the cytoplasm, allowing the complex to be transported into the nucleus. Interestingly, if this phytochrome can enter the nucleus by another mechanism, FHY1 is no longer required for seedling development, indicating that a major function of FHY1 is to chaperone an activated phytochrome into the nucleus. Our experiments suggest that this mechanism uncovered in Arabidopsis is widely conserved among flowering plants.
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