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

点击翻译按钮获取中文摘要

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.