title: Thioredoxin m4 controls photosynthetic alternative electron pathways in Arabidopsis.
abstract: In addition to the linear electron flow, a cyclic electron flow (CEF) around photosystem I occurs in chloroplasts. In CEF, electrons flow back from the donor site of photosystem I to the plastoquinone pool via two main routes: one that involves the Proton Gradient Regulation5 (PGR5)/PGRL1 complex (PGR) and one that is dependent of the NADH dehydrogenase-like complex. While the importance of CEF in photosynthesis and photoprotection has been clearly established, little is known about its regulation. We worked on the assumption of a redox regulation and surveyed the putative role of chloroplastic thioredoxins (TRX). Using Arabidopsis (Arabidopsis thaliana) mutants lacking different TRX isoforms, we demonstrated in vivo that TRXm4 specifically plays a role in the down-regulation of the NADH dehydrogenase-like complex-dependent plastoquinone reduction pathway. This result was confirmed in tobacco (Nicotiana tabacum) plants overexpressing the TRXm4 orthologous gene. In vitro assays performed with isolated chloroplasts and purified TRXm4 indicated that TRXm4 negatively controls the PGR pathway as well. The physiological significance of this regulation was investigated under steady-state photosynthesis and in the pgr5 mutant background. Lack of TRXm4 reversed the growth phenotype of the pgr5 mutant, but it did not compensate for the impaired photosynthesis and photoinhibition sensitivity. This suggests that the physiological role of TRXm4 occurs in vivo via a mechanism distinct from direct up-regulation of CEF.
authors.affiliation: Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7265, Biologie Végétale et Microbiologie Environnementales, 13108 Saint-Paul-lez-Durance, France.
authors.forename: Agathe
authors.initials: A
authors.lastname: Courteille
authors.forename: Simona
authors.initials: S
authors.lastname: Vesa
authors.forename: Ruth
authors.initials: R
authors.lastname: Sanz-Barrio
authors.forename: Anne-Claire
authors.initials: AC
authors.lastname: Cazalé
authors.forename: Noëlle
authors.initials: N
authors.lastname: Becuwe-Linka
authors.forename: Immaculada
authors.initials: I
authors.lastname: Farran
authors.forename: Michel
authors.initials: M
authors.lastname: Havaux
authors.forename: Pascal
authors.initials: P
authors.lastname: Rey
authors.forename: Dominique
authors.initials: D
authors.lastname: Rumeau
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D004579:Electron Transport; D004789:Enzyme Activation; D005033:Ethylmaleimide / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008027:Light; D016254:Mutagenesis, Insertional; D009245:NADH Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D010971:Plastoquinone / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; C465062:PGR5 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D011994:Recombinant Proteins; D002734:Chlorophyll; D013879:Thioredoxins; D009245:NADH Dehydrogenase; D005033:Ethylmaleimide; D010971:Plastoquinone