engleski

Ferredoxin : NADP+ oxidoreductase – TROL interaction defines an overlooked regulatory mechanism in vascular plant photosynthesis

The final step in photosynthetic linear electron transport (LET) chain is the transfer of electrons from reduced ferredoxin (Fd) to NADP+. This reaction is catalysed by the flavoenzime ferredoxin NADP+ oxidoreductase (FNR). In chloroplasts, FNR can be found in either soluble form or bound to membranes via TROL and/or Tic62 proteins. Being an integral membrane protein, TROL (thylakoid rhodanese-like protein) acts as bona fide FNR membrane anchor. TROL has unique molecular architecture dominated by centrally positioned rhodanase-like domain that protrudes into thylakoid lumen and a C-terminally located FNR-binding motif, which is connected to the remaining polypeptide by proline-valine rich stretch dubbed the PEPE region. PEPE most likely enables swivelling of bound FNR and its association with alternative protein complexes. We have demonstrated that the association of FNR with TROL is dynamic and could possibly be modulated by redox ques originating from thylakoid lumen. Intact Arabidopsis chloroplasts isolated from TROL knock-out mutant and treated with ROS-propagating agent methyl viologen produce almost 40% less superoxide anion, as compared to the wild-type chloroplasts. The propagation of other ROS is not affected by TROL deficiency. This highly efficient mechanism of superoxide anion propagation avoidance, triggered by TROL removal, implies that FNR-mediated Fd-to-NADP+ transfer in LET is not the most preferential electron transport pathway downstream of photosystem I (PSI). Thus, FNR-TROL interaction reveals other much faster transfer(s) and can distribute electrons downstream of PSI between energy-conserving and energy-dissipating pathways. Finally, we have in vivo demonstrated the efficiency of this excess energy dissipation by creating TROL overexpression plants that have remarkable conditional phenotype, accumulating high levels of photo protective pigments already at low-light conditions.

photosynthetic electron transport ; Photosystem I ; ROS ; electron paramagnetic resonance

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