小立碗藓光系统I-捕光天线I复合物的结构及其能量传递过程

光系统I（PSI）具有高效的光电转换能力，它依靠捕光蛋白Lhca聚成的捕光天线复合物I（LHCI）捕获光子并快速传递激发能。我们前期解析了豌豆与一种绿藻PSI-LHCI复合物高分辨率结构与能量传递途径，植物登陆以后进化出苔藓、蕨类和种子植物，这些不同进化程度的高等植物的PSI-LHCI结构与捕光机制是重要的科学问题，但目前仍不清楚。本项目选择藓纲模式植物——小立碗藓（Physcomitrella patens）为研究材料，拟采用结构生物学、超快光谱学、分子生物学技术开展交叉研究，解析其PSI-LHCI的结构及其光能吸收、传递和转化的微观动力学过程，揭示从水生向陆生过渡植物的PSI-LHCI结构特征及其与能量传递过程的关系；与豌豆PSI-LHCI复合物对比，揭示高等植物PSI-LHCI结构演化适应不同光环境进行光能吸收、传递和转化的结构基础与机理。研究结果对阐明光反应机理具有重要意义。

Photosynthesis converts light energy from the sun into the chemical energy that is indispensable for almost all life forms on the Earth. To compensate for the low density of light energy available on the Earth's surface, photosynthetic organisms have developed various light-harvesting antennas to harvest and transfer light energy to the core complex of two photosystems, photosystem I (PSI) and photosystem II (PSII), in which charge separation and electron transfer take place. Photosystem I (PSI) is a highly efficient natural light-energy converter, and it relies on Lhca subunits to capture photons and transfer excitation energy to its core complex, and these Lhcas are assembled to form light harvesting complex I (LHCI). In recent years, we have reported the structure of PSI-LHCI complexes from a higher plant (Pisum sativum) and a green alga (Bryopsis corticulans), and comparison between the two PSI-LHCI complexes revealed great differences in both structure and excitation energy transfer pathways during the evolution from green algae to well-adapted terrestrial higher plants. Higher plants include bryophytes, ferns and seed plants, however, little attention was payed into the possible differences in PSI-LHCI among these higher plants at different evolutionary positions. .In this project, we will first analyze the high resolution structure of PSI-LHCI complex from the moss, Physcomitrella patens, which has been developed as a model organism, by crystallization and cryo-electron microscopy, and then to reveal structural differences of PSI-LHCI complexes between moss Physcomitrella patens and seed plant Pisum sativum; and will characterize the energy transfer processes of PSI-LHCI complexes of the different species by time-resolved spectroscopic approaches. Meanwhile, we will construct mutants by molecular biology technology to study the effects of various Lhca subunits on the excitation energy transfer process. By combination of these results, we will reveal the evolution of PSI-LHCI structure, and elucidate the structural basis and the mechanism for its adaption to different light conditions not only to optimize light harvesting but also allow for regulation of excitation energy transfer, which is significant to understand the mechanism of light-energy harvesting, transfer and convertion of PSI-LHCI. Taken together, the results will, from the point of PSI-LHCI, provide new knowledge about how the early land plant lineage had facilitated the adaptation to terrestrial environment, and will provide new clues about how the well-adapted seed plants had facilitated the adaptation to complicated light conditions, which will prompt our understanding on light reaction of photosynthesis.