Charakterisierung des PGRL1/FQR Enzyms auf genetischer, funktioneller und evolutionärer Ebene

线性电子流由两个光系统驱动并产生ATP和NADPH，而循环电子流（CEF）仅产生ATP并仅由光系统I驱动。我们最近确定PGRL 1作为抗霉素A（AA）敏感的CEF变体的核心成分，并发现拟南芥PGRL 1是一种氧化还原活性蛋白，实际上在体外与PGR 5一起作为长期寻找的铁氧还蛋白-质体醌还原酶（FQR）。有趣的是，PGRL 1/PGR 5依赖性CEF的复杂性似乎是从一个涉及PGR 5的过程逐渐演变而来的。（很可能是一种尚未鉴定的具有PGRL 1样功能的蛋白质）在集胞藻中以AA敏感的方式表达（内共生体产生叶绿体的模型），依赖于这两种蛋白质的机制，或者涉及缺乏AA敏感性的含有PGRL 1和PGR 5的超复合物（在衣原体中，具有叶绿体的单细胞生物的模型），或者作为AA敏感性PGRL 1-PGR 5异二聚体（在拟南芥中，多细胞陆地植物的模型）。在这个项目中，我们希望重建PGRL 1和PGR 5的功能进化，从而解决陆地植物（拟南芥），绿色藻类（衣原体）和蓝藻（集胞藻）之间明显存在的功能差异。为此，我们采用蓝细菌集胞藻重建和纯化的蛋白复合物，介导的开花植物和绿色的CEF的类型，以及确定功能类似物PGRL 1（PRIO）在集胞藻，我们在前期工作中获得了强有力的证据。通过系统地识别和表征抑制突变，可以补偿拟南芥中的PGR 5突变的影响，我们将剖析PGRL 1/PGR 5途径与其他电子传递途径在开花植物拟南芥的相互作用。为实现这些目标，我们将重点开展七个子项目。

Whereas linear electron flow is driven by both photosystems and produces ATP and NADPH, the cyclic electron flow (CEF) only generates ATP and is driven by photosystem I alone. We recently identified PGRL1 as a central component of the antimycin A (AA)-sensitive variant of CEF and found that Arabidopsis PGRL1 is a redox-active protein which actually acts in vitro, together with PGR5, as the long sought ferredoxin-plastoquinone reductase (FQR). Interestingly, the complexity of PGRL1/PGR5-dependent CEF seems to have gradually evolved from a process that involves PGR5 (and most likely an as yet not identified protein with PGRL1-like function) in a AA-sensitive manner in Synechocystis (a model for the endosymbiont giving rise to the chloroplast), to mechanisms that rely on both proteins, either involving a PGRL1- and PGR5-containing supercomplex lacking AA-sensitivity (in Chlamydomonas, a model for unicellular organisms with chloroplasts) or as an AA-sensitive PGRL1-PGR5 heterodimer (in Arabidopsis, a model for multicellular land plants). In this project, we wish to reconstruct the evolution of the function of PGRL1 and PGR5, thereby resolving the functional discrepancies which apparently exist between land plants (Arabidopsis), green algae (Chlamydomonas) and cyanobacteria (Synechocystis). To this end, we employ the cyanobacterium Synechocystis to reconstruct and characterise the protein complexes that mediate the flowering-plant- and green-alga- types of CEF, as well as to identify the functional analogue of PGRL1 (PRIO) in Synechocystis, for the existence of which we obtained strong evidence in preliminary work. By systematically identifying and characterising suppressor mutations that can compensate the effects of the pgr5 mutation in Arabidopsis, we will dissect the interplay of the PGRL1/PGR5 pathway with other electron transport pathways in the flowering plant Arabidopsis. To achieve these goals, we will focus on seven sub-projects.