title: New insights into the reduction systems of plastidial thioredoxins point out the unique properties of thioredoxin z from Arabidopsis.
abstract: In plants, thioredoxins (TRX) constitute a large protein disulphide oxidoreductase family comprising 10 plastidial members in Arabidopsis thaliana and subdivided in five types. The f- and m-types regulate enzymes involved mainly in carbon metabolism whereas the x, y, and z types have an antioxidant function. The reduction of TRXm and f in chloroplasts is performed in the light by ferredoxin:thioredoxin reductase (FTR) that uses photosynthetically reduced ferredoxin (Fd) as a reductant. The reduction system of Arabidopsis TRXx, y, and z has never been demonstrated. Recently, a gene encoding an atypical plastidial NADPH-dependent TRX reductase (NTRC) was found. In the present study, gene expression analysis revealed that both reductases are expressed in all organs of Arabidopsis and could potentially serve as electron donors to plastidial TRX. This ability was tested in vitro either with purified NTRC in presence of NADPH or with a light-driven reconstituted system comprising thylakoids and purified Fd and FTR. The results demonstrate that FTR reduces the x and y TRX isoforms but not the recently identified TRXz. Moreover, the results show that NTRC cannot be an efficient alternative reducing system, neither for TRXz nor for the other plastidial TRX. The data reveal that TRXf, m, x, and y, known as redox regulators in the chloroplast, have also the ability to reduce TRXz in vitro. Overall, the present study points out the unique properties of TRXz among plastidial TRX.
authors.affiliation: Institut de Biologie des Plantes, UMR CNRS 8618, Saclay Plant Sciences, Univ Paris-Sud, 91405, Orsay cedex,  France.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Bohrer
authors.forename: Vincent
authors.initials: V
authors.lastname: Massot
authors.forename: Gilles
authors.initials: G
authors.lastname: Innocenti
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Reichheld
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Issakidis-Bourguet
authors.forename: Hélène
authors.initials: H
authors.lastname: Vanacker
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism*; D054479:Chloroplast Thioredoxins / Q000378:metabolism*; D005288:Ferredoxins / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D054479:Chloroplast Thioredoxins; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; C580812:thioredoxin z, Arabidopsis; D013879:Thioredoxins; D009249:NADP; D010088:Oxidoreductases; C021588:ferredoxin-thioredoxin reductase; D013880:Thioredoxin-Disulfide Reductase