Association of Ferredoxin:NADP+ oxidoreductase with the photosynthetic apparatus modulates electron transfer in Chlamydomonas reinhardtii

Abstract

Ferredoxins (FDX) and the FDX:NADP+ oxidoreductase (FNR) represent a key junction of electron transport downstream of photosystem I (PSI). Dynamic recruitment of FNR to the thylakoid membrane has been considered as a potential mechanism to define the fate of photosynthetically derived electrons. In this study, we investigated the functional importance of the association of FNR with the photosynthetic apparatus in Chlamydomonas reinhardtii. In vitro assays based on NADP+ photoreduction measurements as well as NMR chemical shift perturbation analyses showed that FNR preferentially interacts with FDX1 compared to FDX2. Notably, binding of FNR to a PSI supercomplex further enhanced this preference for FDX1 over FDX2, suggesting that FNR is potentially capable of channelling electrons towards distinct routes. NADP+ photoreduction assays and immunoblotting revealed that the association of FNR with the thylakoid membrane including the PSI supercomplex is impaired in the absence of Proton Gradient Regulation 5 (PGR5) and/or Proton Gradient Regulation 5-Like photosynthetic phenotype 1 (PGRL1), implying that both proteins, directly or indirectly, contribute to the recruitment of FNR to the thylakoid membrane. As assessed via in vivo absorption spectroscopy and immunoblotting, PSI was the primary target of photodamage in response to high-light stress in the absence of PGR5 and/or PGRL1. Anoxia preserved the activity of PSI, pointing to enhanced electron donation to O2 as the source of the observed PSI inactivation and degradation. These findings establish another perspective on PGR5/PGRL1 knockout-related phenotypes and potentially interconnect FNR with the regulation of photosynthetic electron transport and PSI photoprotection in C. reinhardtii.

PROTON GRADIENT REGULATION 5 supports linear electron flow to oxidize photosystem I

“…A previous study using two yeast hybrid assays revealed that PGR5 interacts with Fd, and PGRL1 interacts with Fd and FNR (DalCorso et al ). In addition, Mosebach et al () reported that PGR5 and PGRL1 support FNR binding on the thylakoid membranes in Chlamydomonas reinhardtii . Therefore, it is possible that PGR5 and PGRL1 support electron transfer from PSI to Fd and FNR by modulating protein interactions in the vicinity of PSI.…”

“…Furthermore, Fisher and Kramer () reported that Fd and NADPH‐dependent chlorophyll fluorescence rise is achieved by electron donation from Fd to PSII but not PQ‐pool, and the activity was quite small which cannot explain the drastic phenotype of pgr5 mutants. Therefore, it is doubtful whether chlorophyll fluorescence rise assesses the activity of Fd‐dependent CEF‐PSI, and the physiological relevance of PGR5/PGRL1‐dependent CEF is still under debate (Nandha et al , Suorsa et al , , Tikkanen et al , Mosebach et al ). The discordance of PGR5/PGRL1 function would be derived from the lack of direct assessment of Fd during photosynthesis.…”

Electrocatalytic Volleyball: Rapid Nanoconfined Nicotinamide Cycling for Organic Synthesis in Electrode Pores

“…[1] In photosynthesis,s unlight is used to regenerate nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP). [2,3] Fast and efficient recycling occurs within < 100 nm in the chloroplast stroma. [2,3] Fast and efficient recycling occurs within < 100 nm in the chloroplast stroma.…”

“…[2] Ferredoxin (Fd) transfers two electrons,o ne at at ime,f rom photosystem It of erredoxin NADP + reductase (FNR), which is af lavoenzyme that catalyses the conversion of NADP + to NADPH. [2,3] We discovered recently that FNR binds tightly in the pores of an indium tin oxide (ITO) electrode,w here it exhibits rapid electron transfer, reversible electrocatalysis of NADP + /NADPH interconversion, and catalytic coupling to ad ehydrogenase introduced to the solution. [2,3] We discovered recently that FNR binds tightly in the pores of an indium tin oxide (ITO) electrode,w here it exhibits rapid electron transfer, reversible electrocatalysis of NADP + /NADPH interconversion, and catalytic coupling to ad ehydrogenase introduced to the solution.…”

“…[4] Thee lectrode was constructed by electrophoretic deposition of ITO particles (diameter < 50 nm;S upporting Information, Figure S1) onto ac onductive support ( Figure 1A;F igure S1). [2,3] Ap ristine ITOg lass electrode (that is,w ithout an electrophoretically deposited porous ITOl ayer) showed no discernible FNR binding or electrocatalytic activity. [2,3] Ap ristine ITOg lass electrode (that is,w ithout an electrophoretically deposited porous ITOl ayer) showed no discernible FNR binding or electrocatalytic activity.…”