Light/Shade Adaptation of Prochlorothrix Hollandica

这项工作的基本原理是基于这样一个事实，即所有光合生物都必须适应环境光强度的变化，以最大限度地提高光合效率。在强光下，多余的能量必须消散以防止光损伤，而在弱光下，光子捕获必须最大化，以使光合作用有效地进行。我们一直在研究光合原核生物荷兰原绿思（Prochlorothrix hollandica）作为模型系统来研究光合机构的光/暗适应。这种细菌非常适合这些研究，因为它在结构上与高等植物的叶绿体相似，但在实验室中比高等植物或真核藻类更容易操作。我们的工作已经描述了荷兰假单胞菌和植物叶绿体在光/荫适应过程中发生的事件，我们已经表明在这两个系统中发生了类似的机制。总的来说，我们相信分析荷兰假单胞菌的这一过程将更详细地揭示植物应对环境光强度变化所需的途径。具体来说，我们的研究表明，光/暗适应在一定程度上涉及两个独立事件的相互作用。首先，在转向高光后，整个叶绿素色素系统在大约30分钟内重新组织；我们计算出40%的辅助叶绿素色素能够改变它们的取向，从而在强光下改变能量捕获和转移。这种机制似乎是由一种光激活的蛋白激酶控制的。其次，当细胞经历几个小时的强光照射时，光激活的金属蛋白酶活性会降解一部分辅助叶绿素结合蛋白。这种蛋白酶的功能可能是限制在高辐照度下的光子捕获量。准确理解细胞感知强光并触发这些反应的机制将有助于我们理解叶绿体（植物）系统中光合作用是如何被调节的。迄今为止，我们已经克隆了许多编码这些机制中涉及的成分的基因；其中包括编码蛋白激酶的基因。我们目前正在研究光如何影响这些基因的表达，以及激酶的功能如何影响光合作用光收集天线的功能和组织。最后，我们详细研究了在强光下蛋白质水解活性是如何破坏辅助叶绿素蛋白的；辅助叶绿素蛋白可能被类囊体蛋白激酶磷酸化，从而成为蛋白水解的目标。

The rationale for this work is based on the fact that all photosynthetic organisms must adapt to changes in environment light intensity in order to maximize photosynthetic efficiency. At high light, excess energy has to be dissipated to prevent photodamage, while at low light, photon capture has be maximized to allow photosynthesis to proceed efficiently. We have been studying the photosynthetic prokaryote, Prochlorothrix hollandica, as a model system to examine the light/shade adaptation of the photosynthetic apparatus. This bacterium is well-suited to these studies because it is structurally similar to higher plant chloroplasts, but can be manipulated in the lab more easily that higher plants or eukaryotic algae. Our work has characterized the events occurring during light/shade adaptation in both P. hollandica and plant chloroplasts, and we have shown that similar mechanisms occur in both systems. Overall, we believe that analyzing this process in P. hollandica will reveal in more detail the pathway required for plants to handle alterations in environmental light intensity. %%% Specifically, our work has shown that light/shade adaptation involves in part the interplay of two separate events. First, upon a shift to high light, the overall chlorophyll pigment system becomes reorganized in approximately 30 minutes; we calculate 40% of the accessory chlorophyll pigments are capable of changing their orientation such that energy capture and transfer is altered at high light. This mechanism appears to be controlled by a light-activated protein kinase. Second, as cells experience high light for several hours, a light-activated metalloprotease activity degrades a subset of the accessory chlorophyll-binding proteins. The function of this protease is probably to limit the amount of photon capture at high irradiances. Understanding precisely the mechanism(s) by which cells sense high light and trigger these responses will help us understand how photosynthesis is regulated in chloroplast (plant) systems. To date, we have cloned many of the genes encoding the components involved in these mechanisms; these include the genes encoding the protein kinase. We are currently examining how light affects the expression of these genes, and how the function of the kinase affects the function and organization of the photosynthetic light-harvesting antenna. Lastly, we are examining in detail how the proteolytic activity acts to destroy the accessory chlorophyll-proteins in high light; it is possible that the accessory chlorophyll-proteins are targeted for proteolysis by their phosphorylation by the thylakoid protein kinase.