Chloroplast Lipid Composition: Connecting Biophysics to Photosynthetic Function

地球上的生命依赖于植物的光合作用，所以我们必须充分了解光合作用的所有组成系统。尽管在过去的二十年中进行了大量的研究，但我们仍然不知道光合作用（类囊体）膜的脂质组成如何影响光合作用。本项目旨在发现叶绿体生物发生和功能的特定脂质需求。该项目将使用全面的生化、分子和遗传技术来研究模式植物拟南芥的突变体，其中膜脂成分的不同变化与戏剧性的表型相关。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。最终将有可能操纵植物的膜脂组成，以更好地适应特定的环境条件。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理解植物和农业生产系统的温度响应具有广泛的意义。该项目将为研究生和本科生提供机会，接受与农业、林业和其他植物生产领域有关的植物生物学研究的培训和经验。特别是，项目参与者将为一项推广计划做出贡献，该计划使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中注册STEM学科。这一建议侧重于两种具有不同表型的新型突变体。在fab1突变体中，增加16:0导致在2°C下2-3周后光合作用崩溃，并导致叶绿体破坏。已分离出一系列抑制突变，使fab1在2°C下存活。这些基因的克隆和鉴定将为fab1植物中最易受膜改变影响的光合过程提供信息。该项目产生了fad2 fad6突变体等位基因系列，其中含有5%至46%的多不饱和脂肪酸（野生型为77%），这为详细探索类囊体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，质子通过类囊体膜渗漏的增加可能是突变体的一个缺陷。该项目还发现了其他突变体中类囊体蛋白运输不同途径的能力变化，这些研究将扩展到包括fad2 fad6突变体。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学联系起来的机制模型。本提案中描述的互补研究路径有望在应用生物物理原理来理解脂质分子如何促进叶绿体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.