Depletion of leaf‐type ferredoxin‐NADP⁺ oxidoreductase results in the permanent induction of photoprotective mechanisms in Arabidopsis chloroplasts

Abstract

SUMMARYArabidopsis thaliana contains two photosynthetically competent chloroplast-targeted ferredoxin-NADP + oxidoreductase (FNR) isoforms that are largely redundant in their function. Nevertheless, the FNR isoforms also display distinct molecular phenotypes, as only the FNR1 is able to directly bind to the thylakoid membrane. We report the consequences of depletion of FNR in the F 1 (fnr1 · fnr2) and F 2 (fnr1 fnr2) generation plants of the fnr1 and fnr2 single mutant crossings. The fnr1 · fnr2 plants, with a decreased total content of FNR, showed a small and pale green phenotype, accompanied with a marked downregulation of photosynthetic pigment-protein complexes. Specifically, when compared with the wild type (WT), the quantum yield of photosystem II (PSII) electron transport was lower, non-photochemical quenching (NPQ) was higher and the rate of P700 + re-reduction was faster in the mutant plants. The slight over-reduction of the plastoquinone pool detected in the mutants resulted in the adjustment of the reactive oxygen species (ROS) scavenging systems, as both the content and de-epoxidation state of xanthophylls, as well as the content of a-tocopherol, were higher in the leaves of the mutant plants when compared with the WT. The fnr1 fnr2 double mutant plants, which had no detectable FNR and possessed an extremely downregulated photosynthetic machinery, survived only when grown heterotrophically in the presence of sucrose. Intriguingly, the fnr1 fnr2 plants were still capable of sustaining the biogenesis of a few malformed chloroplasts.

ArabidopsisFNRL protein is an NADPH‐dependent chloroplast oxidoreductase resembling bacterial ferredoxin‐NADP+reductases

“…S1). These results are in line with the previous finding showing that inactivation of the two A. thaliana leaf‐type FNR isoforms is lethal (Lintala et al ), further supporting the view that FNRL does not have redundant function(s) with leaf‐type FNRs. It remains to be seen whether principle function of FNRL is as a diaphorase, oxidising NADPH and reducing a specific metabolite, or whether it has protein electron transfer partners.…”

Interaction between plastid and mitochondrial retrograde signalling pathways during changes to plastid redox status

“…Under fluctuating light conditions the stn7 mutant demonstrated a remodelling of the PETC by a reduction in the amount of PSI [24,25]. Similar phenotype has been observed also in other mutants affected in proteins of the acceptor side of PSI [26]. Possibly, the limitation in the electron flow from PSI observed in the rao1 mutants could be explained by a more reduced stroma and lower availability of oxidized electron acceptors.…”

Dynamic Acclimation to High Light in Arabidopsis thaliana Involves Widespread Reengineering of the Leaf Proteome

“…Consistent with this, in gpt2 plants fewer Cyt b 6 f , plastocyanin, ATP synthase and FNR peptides were increased significantly at HL. Various studies have shown the Cyt b 6 f complex, ATP synthase and FNR to be important in determining capacity for both electron transport and carbon fixation (Price et al, 1998; Ruuska et al, 2000; Yamori et al, 2011; Lintala et al, 2012). These data suggest that the ability of gpt2 plants to acclimate the PETC to HL is impaired compared to the WT.…”