The Bacteriophytochrome Photoreceptor From Deinococcus radiodurans: A Paradigm for the Phytochrome Signaling Cascade

植物利用阳光作为光合作用的能量来源，并作为环境线索来协调其发育以适应环境光条件和季节循环。 许多光感受器负责检测这些光信号。 最有影响力的是光敏色素，这是一个吸收红光和远红光的生色团蛋白质家族。 它们充当许多农业上重要过程的光调节开关，包括种子萌发、叶绿体成熟、色素沉着、茎生长、开花和衰老等。 尽管它们很重要，但我们仍然不完全了解光敏色素是如何让植物感知光信号的强度、方向和持续时间的。 这种理解的一个主要障碍是缺乏简单的遗传学上易于处理的模型来研究光敏色素，而不需要其他光感受器和光合作用的复杂性。 我们已经同时克服了这些问题，最近在非光合细菌，耐辐射异常球菌中发现了单一的光敏色素样光感受器系统[Davis等人（1999）Science 286：2517-2520]。 与光敏色素一样，D.耐辐射细菌光敏色素光感受器（BphP）吸收红光和远红光。 对BphP的研究表明，它作为一种蛋白激酶，通过磷酸化其他蛋白质开始光传感。 最终，这种信号刺激细菌产生类胡萝卜素，通常用于保护植物免受强光条件的色素。 本课题的主要目的是研究D. BphP光敏色素，以了解其结构和作用机制。 将在生物化学水平上表征BphP感光体，以确定其天然发色团的身份及其与蛋白质连接的方式。 将确定合成发色团的途径。 将尝试使蛋白质结晶，以便确定其结构。 通过一些方法，导致从BphP到光刺激类胡萝卜素生产的生化步骤将被定义。这项工作的完成将开始提供第一个描述光敏色素信号转导途径，然后可以作为一个框架，了解光敏色素如何在作物植物的工作。

Plants use sunlight as a source of energy for photosynthesis and as an environmental cue to coordinate their development to the ambient light conditions and seasonal cycles. A number of photoreceptors are responsible for detecting these light signals. The most influential are the phytochromes, a family of chromophore-bearing proteins that absorbs red and far-red light. They act as light-regulated switches for a number of agriculturally important processes, including seed germination, chloroplast maturation, pigmentation, stem growth, flowering, and senescence to name a few. Despite their importance, we still do not fully understand how phytochromes allow plants to sense the intensity, direction, and duration of the light signal. A major barrier to this understanding has been the dearth of simple genetically-tractable models for the study of phytochromes without the complications of other photoreceptors and photosynthesis. We have simultaneously overcome these problems with the recent discovery of a single phytochrome-like photoreceptor system in the non-photosynthetic bacterium, Deinococcus radiodurans [Davis et al. (1999) Science 286: 2517-2520]. Like phytochromes, the D. radiodurans bacteriophytochrome photoreceptor (BphP) absorbs red and far-red light. Studies on BphP suggest that it acts as a protein kinase that begins light sensing by phosphorylating other proteins. Ultimately this signal stimulates the bacterium to produce carotenoids, pigments typically used to protect plants from high light conditions. The goal of this project is to study the D. radiodurans BphP phytochrome to understand its structure and mechanism of action. The BphP photoreceptor will be characterized at the biochemical level to determine the identity of its natural chromophore and the way it is linked to the protein. The pathway that synthesizes the chromophore will be determined. Attempts will be made to crystallize the protein so that its structure can be defined. Via a number of methods, the biochemical steps that lead from BphP to light-stimulated carotenoid production will be defined. Completion of this work will begin to provide the first description of a phytochrome signal transduction pathway that can then be used as a framework for understanding how phytochromes work in crop plants.