Seryl-Phosphorylation / Dephosphorylation of Plant Metabolic Enzymes in Leaves (PEPC) and Root Nodules (SuSy, PEPC)

叶 (PEPC) 和根瘤 (SuSy, PEPC) 中植物代谢酶的丝酰磷酸化/去磷酸化

• 批准号: 9727236
• 负责人: Raymond Chollet
• 金额: $ 46.43万
• 依托单位: University of Nebraska-Lincoln
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-05-01 至 2003-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9727236&HistoricalAwards=false
• 关键词: Seryl; Phosphorylation; Dephosphorylation; Plant; Metabolic

9727236 Chollet This renewal project is focused on this laboratory's long-standing interest in the control of plant primary metabolism by phosphorylation/ dephosphorylation cycles of regulatory proteins. The two related areas of overall investigation specifically concern phosphoenolpyruvate carboxylase (PEPC) and sucrose synthase (SuSy), two target enzymes known to undergo seryl-phosphorylation in intact leaves and N2-fixing legume nodules. While cytosolic PEPC is best known for its cardinal role in catalyzing the fixation of atmospheric CO2 during C4 photosynthesis and Crassulacean acid metabolism (CAM), this ubiquitous plant carboxylase also functions in a vast array of nonphotosynthetic contexts, including C/N-metabolism in general (e.g., in C3 leaves) and in the more specialized cases of N2-fixing root nodules, leaf guard cells, and seed germination. The multifaceted nature of plant PEPC makes its intricate control by a highly regulated, Ca2+-independent protein-Ser/Thr kinase (PEPC-kinase) and an opposing protein phosphatase-2A an extremely attractive target for continued study. Accordingly, two of the three specific research objectives of this renewal project focus on (1) C4 and/or CAM PEPC-kinase, and (2)its requisite but seemingly diverse signaling pathways in leaves (C4, Ca, CAM) and root nodules. Recent work has shown that SuSy, in addition to PEPC, is a target for seryl-phosphorylation by a soluble, Ca2+-dependent protein kinase in two physiologically distinct plant "sink" tissues: elongating maize leaves and soybean root nodules. These are potentially significant observations because virtually nothing is known of the posttranslational control of SuSy activity or of how the enzyme physically partitions between the plasma membrane and cytosol in plants. Clearly, reversible changes in its phosphorylation state are a possible but as yet unexplored mechanism for these phenomena. These newly emerged questions about plant SuSy will be addressed in Objective 3 of this renewal project by the continued biochemical and molecular investigation of the phosphorylation/dephosphorylation of nodulin-100, the nodule-enhanced form of this sucrose-cleaving enzyme in soybean. The major significance of this basic research project is its delineation of important fundamental details of the regulation of carbon-dioxide assimilation (by PEPC) and sucrose cleavage (by SuSy) by reversible protein phosphorylation in various tissues of agronomically important crop species, including maize, tobacco, and soybeans. At the same time, the results may provide the requisite underpinning for the constructive manipulation of plant carbon/nitrogen-metabolism and its control mechanisms through biotechnology. It must be emphasized that PEPC and SuSy represent two of the handful of documented examples of plant metabolic enzymes targeted by protein kinases and protein phosphatases in planta. Thus, the research will provide much-needed insight into the control of plant metabolism by reversible protein phosphorylation.

9727236 Chollet这个更新项目的重点是这个实验室的长期兴趣在植物初级代谢的调控蛋白的磷酸化/去磷酸化循环的控制。整体调查的两个相关领域特别关注磷酸烯醇式丙酮酸羧化酶（PEPC）和蔗糖合成酶（SuSy），这两种靶酶已知在完整叶片和固氮豆科植物根瘤中进行丝氨酰磷酸化。虽然胞质PEPC最为人所知的是其在C4光合作用和景天科酸代谢（CAM）期间催化大气CO2固定的主要作用，但这种普遍存在的植物羧化酶也在大量的非光合作用环境中起作用，包括一般的C/N代谢（例如，在C3叶中）以及在固氮根瘤、叶保卫细胞和种子萌发的更特殊的情况下。植物PEPC的多方面性质使得其通过高度调节的、Ca 2+非依赖性蛋白质-Ser/Thr激酶（PEPC-激酶）和相反的蛋白质磷酸酶-2A的复杂控制成为继续研究的非常有吸引力的目标。 因此，该更新项目的三个具体研究目标中的两个集中在（1）C4和/或CAM PEPC激酶，以及（2）其在叶（C4，Ca，CAM）和根瘤中必需但看似不同的信号通路。 最近的研究表明，除了PEPC，SuSy是一个目标的丝氨酸磷酸化的可溶性，Ca 2+依赖性蛋白激酶在两个生理上不同的植物“汇”组织：延长玉米叶和大豆根瘤。这些都是潜在的重要观察，因为几乎没有什么是已知的翻译后控制SuSy活性或酶如何物理分区之间的质膜和细胞质在植物中。显然，其磷酸化状态的可逆变化是这些现象的可能但尚未探索的机制。关于植物SuSy的这些新出现的问题将在本更新项目的目标3中通过对大豆中这种蔗糖裂解酶的结节增强形式--大豆球蛋白-100的磷酸化/去磷酸化的持续生物化学和分子研究来解决。 该基础研究项目的主要意义在于其描绘了重要的基本细节，即通过可逆的蛋白质磷酸化在农业上重要的作物物种（包括玉米、烟草和大豆）的各种组织中调节二氧化碳同化（通过PEPC）和蔗糖裂解（通过SuSy）。同时，这些结果可能为通过生物技术建设性地操纵植物碳/氮代谢及其控制机制提供必要的基础。必须强调的是，PEPC和SuSy代表了植物中蛋白激酶和蛋白磷酸酶靶向的植物代谢酶的少数记录实例中的两个。因此，这项研究将为可逆蛋白质磷酸化控制植物代谢提供急需的见解。