Role of molecular chaperone HSP90C in regulating plant photosynthesis

热休克蛋白90 （HSP90）是一种分子伴侣，它有助于折叠各种蛋白质（称为HSP90底物或客户端），其中许多是蛋白激酶和转录因子，在细胞信号通路中起关键作用。在高等植物中，HSP90亚型存在于细胞质和细胞器中。与细胞质内的HSP90亚型（称为HSP90A）相比，叶绿体定位的HSP90C的作用机制，特别是客户谱仍然知之甚少。我的长期研究目标是了解HSP90在植物发育、细胞器功能和植物适应环境变化中的作用和作用机制。本研究计划的短期目标是研究叶绿体HSP90C的作用机制。我们的研究表明，通过转基因诱导的基因沉默下调HSP90C会导致表型多样化和叶绿体生物发生受损。然而，转基因植物叶绿体功能障碍的机制以及HSP90C过表达是否能够刺激光合能力尚不清楚。本研究计划的目的是通过生物化学、细胞学、生理学和蛋白质组学的方法来研究HSP90C调控光合能力的机制。我们假设高表达HSP90C可以提高光合能力。研究重点将主要集中在两个方面：1)了解HSP90C调节其特定客户蛋白功能的机制；2)了解过表达HSP90C是否以及如何提高整体光合速率。首先，为了了解HSP90C的作用机制，我们将研究HSP90C在介导类囊体管腔靶向氧进化复杂蛋白PsbO（也称为OE33）中的作用，我们之前已经证明该蛋白与HSP90C相互作用。我们推测，HSP90C在叶绿体基质中陪伴OE33，并帮助其类囊体腔移位。我们将通过生化和细胞方法研究OE33在HSP90C过表达和共抑制系中的叶绿体靶向效率。其次，为了了解HSP90C在促进植物光合能力方面的作用，我们将使用HSP90C过表达的转基因品系。转基因植物的光合能力将通过气体交换和叶绿素荧光分析进行深入研究。此外，还将分析光合作用的最终产物或中间产物的积累。叶绿体是植物细胞中进行光合作用的独特细胞器。本研究以叶绿体HSP90C为研究对象，研究分子伴侣对叶绿体发育、功能及光合成分活性的调控作用。该研究将揭示HSP90在类囊体蛋白靶向和蛋白复合物组装中的作用机制，从而对生命的复杂性提供批判性的观点。本研究通过分析HSP90C在调控光合能力中的作用，探讨了复杂光合作用过程中新的主要调控因子。这项研究的结果将有可能为提高光合能力的转基因植物品系提供新的策略，从而提高粮食作物的产量。这项研究还将为哺乳动物细胞的研究提供额外的信息，因为HSP90是一种高度保守的蛋白质，正被用作癌症研究的靶点。

The heat shock protein 90 (HSP90) is a molecular chaperone which aids in folding a variety of proteins (termed HSP90 substrates or clients), many of which are protein kinases and transcription factors playing key roles in cellular signaling pathways. In higher plants, HSP90 isoforms are localized in both cytoplasm and organelles. Compared with those of the cytosolic HSP90 isoforms (termed HSP90A), the mechanism of action and especially the client spectrum of the chloroplast localized HSP90C are still poorly understood. My long-term research goal is to understand the role and mechanism of action of HSP90 in plant development, organelle functions, and in plant adaptation to environmental changes. A short-term goal of this research program is to study the mechanism of action of the chloroplast HSP90C. Our research has demonstrated that down-regulation of HSP90C by transgene-induced gene silencing results in a variegated phenotype and impaired chloroplast biogenesis. However, the mechanism that underlies the malfunction of chloroplast in the transgenic plants, and whether overexpression of HSP90C is able to stimulate photosynthetic capacity is unclear. The objective of this proposed research program is to investigate the mechanism by which HSP90C regulates the photosynthetic capacity through a battery of biochemical, cellular, physiological and proteomics approaches. We hypothesize that higher expression of HSP90C enhances photosynthesis capacity. Research focus will be mainly on two broad goals: 1) to understand the mechanism of HSP90C in modulating the function of its specific client proteins; 2) to understand whether and how overexpression of HSP90C enhances the overall photosynthesis rate. First, to understand the mechanism of action of HSP90C, we will investigate the role of HSP90C in mediating the thylakoid lumen targeting of an oxygen evolving complex protein, PsbO (also termed OE33), which we previously demonstrated to interact with HSP90C. We hypothesize that HSP90C chaperones OE33 in the chloroplast stroma and aids its thylakoid lumen translocation. We will investigate the chloroplast targeting efficiency of OE33 in both HSP90C overexpression and cosuppression lines by means of biochemical and cellular approaches. Second, to understand the role of HSP90C in promoting plant photosynthesis capacity, we will use the HSP90C overexpression transgenic lines. The photosynthetic capacity of transgenic plants will be thoroughly investigated using gas exchange and chlorophyll fluorescence analyses. Moreover, the accumulation of end products or intermediates of photosynthesis will be analyzed. Chloroplast is the unique organelle of a plant cell where the photosynthesis takes place. This proposed research employs chloroplast HSP90C to study the role of molecular chaperones which regulate the chloroplast development, function and photosynthetic component activity. The study will reveal the mechanism of action of HSP90 in thylakoid protein targeting and protein complex assembly, thus providing a critical view of the complexity of life. By analyzing the role of HSP90C in regulating photosynthesis capacity, this study investigates new master regulators of the complicated photosynthesis process. The results of this research will potentially provide novel strategies to genetically engineer plant lines with higher photosynthetic capacity, thus better yield for grain crops. This study will also provide additional information for research in mammalian cells since HSP90 is a highly conserved protein and is being used as a target in cancer research.