WCEVC
Tryptophan-cysteine-glutamic acid-valine-cysteine motif
WCGPC
Tryptophan-cysteine-glycine-proline-cysteine motif
WCRKC
Atypical thioredoxin with tryptophan-cysteine-arginine-lysinecysteine active site
YF
Tyrosine-phenylalanine motif
1 Introduction
Redox regulation plays a crucial role in a large number of plant cellular processes
(Geigenberger and Fernie 2014). Thioredoxins (TRX), small polypeptides of
12–13 kDa with protein disulfide reductase activity, catalyze Cys-based posttranslational modifications, which affect the conformation and function of a large number
of proteins. Plants harbor a multiplicity of TRX isoforms and reduction pathways
(Lemaire et al. 2007; Meyer et al. 2012; Geigenberger et al. 2017). In Arabidopsis
thaliana, the gene family of typical TRX encodes for up to 20 different isoforms
located in different subcellular compartments. While the plastid uses ferredoxin
(FDX) to reduce TRX via the FDX TRX reductase (FTR), extraplastidial TRX are
reduced by NADPH-dependent TRX reductases (NTR). Plastids also contain an
unusual NADPH-dependent TRX system termed NTRC, which is characterized by a
tethered TRX domain, providing a complete NTR-TRX system in a single polypeptide. In the last years, progress has been made to improve our understanding of the
organization and biological roles of this complex thiol-based redox network. The
aim of this review is to provide a synthesis of these recent evolvements focusing on
the emerging roles of TRX in regulating metabolism, stress responses, development,
and gene expression of higher plants.
2 The Plastidial Thioredoxin Systems
2.1 Ferredoxin Thioredoxin Reductase-Dependent
Thioredoxin System
2.1.1 Plastids Contain the Most Diverse TRX System of Higher Plant
Cells
About half of the total TRX isoforms in Arabidopsis cells are localized in the stroma
of plastids (Meyer et al. 2012; Geigenberger et al. 2017). Typical TRX consist of a
small single TRX domain carrying a highly conserved motif (WCGPC) in the redoxactive site, which modulates the redox state of target enzymes by the reversible
exchange of an oxidized disulfide bridge to two reduced thiols. The ten typical TRX
isoforms localized in plastids are divided into five types, namely f (1–2), m (1–4), x,
y (1–2), and z. Interestingly, the two TRX isoforms f1 and f2 contain an additional
226
I. Thormählen et al.
Tryptophan-cysteine-glutamic acid-valine-cysteine motif
WCGPC
Tryptophan-cysteine-glycine-proline-cysteine motif
WCRKC
Atypical thioredoxin with tryptophan-cysteine-arginine-lysinecysteine active site
YF
Tyrosine-phenylalanine motif
1 Introduction
Redox regulation plays a crucial role in a large number of plant cellular processes
(Geigenberger and Fernie 2014). Thioredoxins (TRX), small polypeptides of
12–13 kDa with protein disulfide reductase activity, catalyze Cys-based posttranslational modifications, which affect the conformation and function of a large number
of proteins. Plants harbor a multiplicity of TRX isoforms and reduction pathways
(Lemaire et al. 2007; Meyer et al. 2012; Geigenberger et al. 2017). In Arabidopsis
thaliana, the gene family of typical TRX encodes for up to 20 different isoforms
located in different subcellular compartments. While the plastid uses ferredoxin
(FDX) to reduce TRX via the FDX TRX reductase (FTR), extraplastidial TRX are
reduced by NADPH-dependent TRX reductases (NTR). Plastids also contain an
unusual NADPH-dependent TRX system termed NTRC, which is characterized by a
tethered TRX domain, providing a complete NTR-TRX system in a single polypeptide. In the last years, progress has been made to improve our understanding of the
organization and biological roles of this complex thiol-based redox network. The
aim of this review is to provide a synthesis of these recent evolvements focusing on
the emerging roles of TRX in regulating metabolism, stress responses, development,
and gene expression of higher plants.
2 The Plastidial Thioredoxin Systems
2.1 Ferredoxin Thioredoxin Reductase-Dependent
Thioredoxin System
2.1.1 Plastids Contain the Most Diverse TRX System of Higher Plant
Cells
About half of the total TRX isoforms in Arabidopsis cells are localized in the stroma
of plastids (Meyer et al. 2012; Geigenberger et al. 2017). Typical TRX consist of a
small single TRX domain carrying a highly conserved motif (WCGPC) in the redoxactive site, which modulates the redox state of target enzymes by the reversible
exchange of an oxidized disulfide bridge to two reduced thiols. The ten typical TRX
isoforms localized in plastids are divided into five types, namely f (1–2), m (1–4), x,
y (1–2), and z. Interestingly, the two TRX isoforms f1 and f2 contain an additional
226
I. Thormählen et al.