Chloroplast Lipid Composition: Connecting Biophysics to Photosynthetic Function

地球上的生命依赖于植物的光合作用，因此我们必须充分了解影响光合作用功能的所有组成系统。尽管在过去的二十年里进行了大量的研究，但我们仍然不知道光合作用(类囊体膜)的脂质成分是如何影响光合作用的。该项目旨在发现叶绿体生物发生和功能所需的特殊脂类。该项目将使用全方位的生化、分子和遗传技术来研究模式植物拟南芥的突变体，在这些突变体中，膜脂组成的不同变化与戏剧性的表型有关。所获得的知识将帮助科学家预测环境变化对植物生长和作物生产力可能产生的后果。最终，操纵植物的膜脂成分以更好地适应特定的环境条件将成为可能。由于光合作用是植物生产力的核心，在突变体中观察到的广泛的温度依赖效应对于理解植物和农业生产系统的温度反应具有广泛的意义。该项目将为研究生和本科生提供接受与农业、林业和其他植物生产领域相关的植物生物学研究的培训和经验的机会。特别是，项目参与者将为一个推广计划做出贡献，该计划利用体验式学习和同伴指导来鼓励美国原住民高中生在大学注册STEM学科。这项提议集中在两个新的具有不同表型的突变体类别。在FAB1突变体中，16：0的增加导致在2℃下2-3周后光合作用的崩溃，并导致叶绿体的破坏。一组允许FAB1在2℃下存活的抑制突变已经被分离出来。这些基因的克隆和鉴定将提供有关FAB1植物中最容易受到膜变化影响的光合作用过程的信息。该项目已经产生了一系列含有5%到46%多不饱和脂肪酸(野生型为77%)的fad2 fad6突变体，这为详细探索类囊体膜不饱和与叶绿体功能之间的关系提供了第一次机会。分析表明，通过类囊体膜的质子泄漏增加是突变体的一个可能缺陷。该项目还发现在其他突变体中不同的类囊体蛋白运输途径的能力发生了变化，这些研究将扩大到包括fad2和fad6突变体。所获得的结果将允许开发和测试将突变体的生理表型与膜脂结构的生物物理联系起来的机制模型。这项建议中描述的补充研究途径有望在应用生物物理学原理理解脂分子如何促进叶绿体的功能和植物对环境变化的反应方面取得重要进展。

Life on Earth depends on plant photosynthesis, so it is vital that we fully understand all the component systems that contribute to photosynthetic function. Despite considerable research effort over the last twenty years, we still do not know how the lipid composition of the photosynthetic (thylakoid) membrane affects photosynthesis. This project aims to discover the particular lipid requirements for chloroplast biogenesis and function. The project will use the full range of biochemical, molecular and genetic techniques to investigate mutants of the model plant, Arabidopsis, in which different changes in membrane lipid composition are associated with dramatic phenotypes. The knowledge gained will help scientists predict the likely consequences of environmental changes on plant growth and crop productivity. Eventually it will be possible to manipulate membrane lipid composition of plants to better suit particular environmental conditions. Because photosynthesis is central to plant productivity, the extensive temperature-dependent effects observed in the mutants have wide implications for understanding the temperature responses of plants, and agricultural production systems. The project will provide opportunities for graduate and undergraduate students to receive training and experience in plant biology research relevant to agriculture, forestry and other fields of plant production. In particular, the project participants will contribute to an outreach program that uses experiential learning and peer mentoring to encourage Native American high school students to enroll in STEM disciplines in college.This proposal focuses on two new classes of mutants with distinct phenotypes. In the fab1 mutant, an increase in 16:0 results in the collapse of photosynthesis after 2-3 weeks at 2°C, and to destruction of chloroplasts. A collection of suppressor mutations that allow survival of fab1 at 2°C have been isolated. Cloning and characterization of these will provide information about the photosynthetic processes that are most susceptible to the membrane alterations in fab1 plants. The project has generated an allelic series of fad2 fad6 mutants containing 5% to 46% polyunsaturated fatty acids (vs. 77% in wild type) that provide the first opportunity to explore, in detail, the relationship between thylakoid unsaturation and chloroplast function. Analyses indicate that an increase in leakage of protons through the thylakoid membrane is one possible defect in the mutants. The project has also discovered alterations in the capacities of different pathways of thylakoid protein transport in other mutants and these investigations will be extended to include the fad2 fad6 mutants. The results obtained will permit the development and testing of mechanistic models that relate the physiological phenotypes of the mutants to the biophysics of membrane lipid structure. The complementary paths of investigation described in this proposal promise important advances in the application of biophysical principles to understanding how lipid molecules contribute to the functioning of chloroplasts and the responses of plants to environmental change.