Abstract
During photosynthesis, electron transport is necessary for carbon assimilation and must be regulated to minimize free radical damage. There is a longstanding controversy over the role of a critical enzyme in this process (ferredoxin:NADP(H) oxidoreductase, or FNR), and in particular its location within chloroplasts. Here we use immunogold labelling to prove that FNR previously assigned as soluble is in fact membrane associated. We combined this technique with a genetic approach in the model plant Arabidopsis to show that the distribution of this enzyme between different membrane regions depends on its interaction with specific tether proteins. We further demonstrate a correlation between the interaction of FNR with different proteins and the activity of alternative photosynthetic electron transport pathways. This supports a role for FNR location in regulating photosynthetic electron flow during the transition from dark to light.
Highlights
41 Photosynthetic carbon assimilation in chloroplasts requires NADPH. This is generated by the enzyme ferredoxin:NADP(H) oxidoreductase (FNR) using electrons from ferredoxin (Fd), which is reduced on excitation of photosystem I (PSI) (Shin et al., 1963)
2) There is no statistical difference between staining density in the grana and stroma, meaning that even the low level detected in the stroma is likely due to the orientation of label attached to membrane associated FNR. 3) Cyt f is detected at significantly higher density in the stroma than the cytosol by IGL-transmission electron microscopy (TEM) (Figure 1 Supplement 2, Supplementary File 2b)
The most likely explanation for this is that the aggressive cell disruption procedures, or osmotic shock followed by solubilisation for BNP, disrupt weak associations of FNR with other membrane complexes (Andersen et al, 1992, Zhang et al, 2001), or possibly even the membrane itself (Grzyb et al, 2018, Grzyb et al, 2008)
Summary
FNR location regulates electron transport 5 Manuela Kramer[1,2], Melvin Rodriguez-Heredia[1], Francesco Saccon[1], Laura 6 Mosebach[3], Manuel Twachtmann[2], Anja Krieger-Liszkay[4], Chris Duffy[1], Rob Knell[1 7] Giovanni Finazzi[5], Guy Hanke[1,2]. 9 1School of Biochemistry and Chemistry, Queen Mary University of London, Mile End Rd, London E1 4NS, United Kingdom 2Department of Plant Physiology, Faculty of Biology and Chemistry, University of Osnabrück, 49076, Germany 3Institute of Plant Biology and Biotechnology, University of Münster, Münster, Germany 4Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France 5Laboratoire de Physiologie Cellulaire et Végétale, UMR 5168, Centre National de la Recherche Scientifique (CNRS), Commissariat al’Energie Atomique et aux Energies Alternatives (CEA), Université Grenoble Alpes, Institut National Recherche Agronomique (INRA), Institut de Recherche en Sciences et Technologies pour le Vivant (iRTSV), CEA Grenoble, F-38054 Grenoble cedex 9, France
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