engleski

Molecular basis of alternative electron partitioning in photosynthesis

In vascular plant photosynthesis several electron transport chains have been recognized. Linear electron transport chain (LET) transfers electrons generated by photosystems II and I to a small iron-sulphur protein ferredoxin (Fd). Fd acts simultaneously as a bottleneck and as a hub which distributes high-energy electrons to a multitude of enzymes. The dominant pathway in chloroplasts is, however, the one that produces NADPH, by the activity of ferredoxin-NADP+-oxidoreductase (FNR). FNR is a soluble protein that exists in several isoforms and utilizes two reduced Fds to produce one molecule of NADPH. In order to function efficiently Fd/FNR redox chemistry has to be constantly poised. The question remains how is the partitioning of electrons between various energy-conserving and -dissipating pathways achieved. We have previously shown that thylakoid rhodanase-like protein TROL acts as a bona fide membrane attachment point for the FNR, although other associations with thylakoid and inner envelope membranes have been described. We have proposed a scheme for the dynamic FNR recruitment to TROL. We posit that TROL-FNR interaction represents branching point between electron-conserving and electron-dissipating pathways. Without the TROL, light-dependent O2.- generation is reduced, while the generation of other ROS is enhanced. We propose that other Fd-dependent pathways downstream of PSI and different from the linear electron transfer become dominant by the dynamic detachment of FNR form TROL, thus suggesting a novel mechanism of photosynthesis regulation. Alternatively, efficient scavenging of O2.- by FNR-dependent pathways can be envisaged.

photosystem I; redox regulation and signaling; regulation of electron flow

nije evidentirano