Plastidial thioredoxin z interacts with two fructokinase-like proteins in a thiol-dependent manner: evidence for an essential role in chloroplast development in Arabidopsis and Nicotiana benthamiana.
Here, we characterize a plastidial thioredoxin (TRX) isoform from Arabidopsis thaliana that defines a previously unknown branch of plastidial TRXs lying between x- and y-type TRXs and thus was named TRX z. An Arabidopsis knockout mutant of TRX z had a severe albino phenotype and was inhibited in chloroplast development. Quantitative real-time RT-PCR analysis of the mutant suggested that the expressions of genes that depend on a plastid-encoded RNA polymerase (PEP) were specifically decreased. Similar results were obtained upon virus-induced gene silencing (VIGS) of the TRX z ortholog in Nicotiana benthamiana. We found that two fructokinase-like proteins (FLN1 and FLN2), members of the pfkB-carbohydrate kinase family, were potential TRX z target proteins and identified conserved Cys residues mediating the FLN-TRX z interaction. VIGS in N. benthamiana and inducible RNA interference in Arabidopsis of FLNs also led to a repression of PEP-dependent gene transcription. Remarkably, recombinant FLNs displayed no detectable sugar-phosphorylating activity, and amino acid substitutions within the predicted active site imply that the FLNs have acquired a new function, which might be regulatory rather than metabolic. We were able to show that the FLN2 redox state changes in vivo during light/dark transitions and that this change is mediated by TRX z. Taken together, our data strongly suggest an important role for TRX z and both FLNs in the regulation of PEP-dependent transcription in chloroplasts.
Max-Planck Institute of Molecular Plant Physiology, Golm, Germany. arsova@mpimp-golm.mpg.de
Borjana
B
Arsova
Ursula
U
Hoja
Matthias
M
Wimmelbacher
Eva
E
Greiner
Suayib
S
Ustün
Michael
M
Melzer
Kerstin
K
Petersen
Wolfgang
W
Lein
Frederik
F
Börnke
D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D003545:Cysteine / Q000378:metabolism; D003624:Darkness; D005631:Fructokinases / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010641:Phenotype; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D011994:Recombinant Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism*; D014026:Nicotiana / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; D011994:Recombinant Proteins; D013438:Sulfhydryl Compounds; D013879:Thioredoxins; C000594290:FLN1 protein, Arabidopsis; C000605310:FLN2 protein, Arabidopsis; D005631:Fructokinases; D017853:Phosphotransferases (Alcohol Group Acceptor); C046173:fructokinase; D003545:Cysteine