拟南芥PBF蛋白调控光系统I生物发生的分子机理研究

Photosystem I (PSI) represents one of the largest and most complex macromolecular assemblies in nature. Its subunits are encoded by both plastid and nucleus genome. The biogenesis of the PSI complex requires a spatially and temporally coordinated assembly process with highly ordered sequence, and necessitates array of regulatory factors to fine tuning this complicated process at multi-level. At present, although several auxiliary factors involved in PSI biogenesis have been characterized, the molecular mechanisms underlying PSI biogenesis remains to be dissected. Identification of new regulatory factors will obviously provide new evidence for the regulation process of PSI biogenesis. To this end, we have screened for a set of PSI-deficiency mutants in Arabidopsis thaliana, and one of them, which is termed as pbf（for PSI Biogenesis Factor）, is severely impaired in PSI function and in the accumulation of PSI complex, indicating a essential role of PBF duing the PSI biogenesis process. In this study, we aim to functionally characterize PBF factor, a new regulator for PSI biogenesis, through combining biophysics, molecular genetics, biochemistry, molecular biology and plant physiology, and at the same time to reveal the limiting steps in PSI complex accumulation in the pbf mutant. Moreover, by screening for PBF targeting proteins and analyzing the interaction between them, our study will provide new insight into the molecular details of PSI biogenesis process and especially the regulatory mechanisms during this process.

光系统I（PSI）是自然界中最大也是最复杂的大分子组装体之一，其亚基由叶绿体基因组和细胞核基因组共同编码。PSI的生物发生是一个多步骤却非常有序的过程，需要众多调控因子协同来完成，并且需要这些因子从时间和空间上、在多个层次上进行精细调控。到目前为止，虽然已经鉴定了一些PSI生物发生的调控因子；但是，PSI复合物生物发生的分子机理仍然不清楚。因此，发现新的调控因子无疑会对PSI生物发生的分子细节提供新的认识。我们在拟南芥中筛选到一个新的PSI生物发生缺陷型突变体pbf（PSI Biogenesis Factor），该突变体中PSI复合物的积累量及其活性都显著降低。本研究的目标是通过分子遗传学、分子生物学以及植物生理生化等技术，阐明调控因子PBF控制PSI积累的限制步骤，并通过筛选和研究PBF与靶蛋白之间的相互作用关系，以期揭示PBF调控PSI复合物生物发生的分子机理。

鉴定PSI合成的调控因子对于研究其生物发生和功能具有重要意义。我们以拟南芥为材料，通过光谱学的方法筛选到了一些PSI功能缺陷突变体，并建立了系统的研究体系。本项目对已经筛选到的PSI功能缺陷突变体pbf进行了深入研究。发现PBF即VTE6，是参与叶绿醌植基侧链合成的关键酶。叶绿醌是光系统I特有的电子传递载体，VTE6突变体中检测不到叶绿醌的存在。突变体中PSI复合物的积累量及其活性都显著降低。突变体中PSI的核心亚基PsaA/B能正常合成，并组装成有功能的复合物。但是周转加快。高光条件下，突变体的PSI复合物降解加快。本项目的研究揭示了VTE6参与叶绿醌植基侧链合成途径的遗传学证据，并揭示了叶绿醌在高光条件下维持PSI稳定性的重要功能。