Glutaredoxins and thioredoxins in plants

During the 70s and 80s two plant thioredoxin systems were identified. The chloroplastic system is composed of a ferredoxin-dependent thioredoxin, with two thioredoxin types (m and f) regulating the activity of enzymes implicated in photosynthetic carbon assimilation. In the cytosol of heterotrophic tissues, an NADP dependent thioredoxin reductase and a thioredoxin (h) were identified. The first plant glutaredoxin was only identified later, in 1994. Our view of plant thioredoxins and glutaredoxins was profoundly modified by the sequencing programs which revealed an unexpected number of genes encoding not only the previously identified disulfide reductases, but also numerous new types. At the same time it became clear that plant genomes encode chloroplastic, cytosolic and mitochondrial peroxiredoxins, suggesting a major role for redoxins in anti-oxidant defense. Efficient proteomics approaches were developed allowing the characterization of numerous thioredoxin target proteins. They are implicated in different aspects of plant life including development and adaptation to environmental changes and stresses. The most important challenge for the next years will probably be to identify in planta which redoxin reduces which target, a question which remains unsolved due to the low specificities of redoxins in vitro and the numerous redundancies which in most cases mask the phenotype of redoxin mutants.