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Characterization of peroxiredoxin, thioredoxin and NADPH thioredoxin reductase genes

AuthorsMatamoros Galindo, Manuel Ángel ; Ramos Escribano, Javier ; Becana Ausejo, Manuel
Issue DateJul-2011
Citation10th International Conference on Reactive Oxygen and Nitrogen Species in Plants (Budapest. 2011)
AbstractThioredoxins (Trxs) are ubiquitous proteins with a single disulfide bridge which are involved in the reduction of peroxiredoxins and in many other redox reactions1,2. Plants contain eight types of Trx isoforms, which are mainly localized to the plastids ( f, m, x, y, z), cytosol (h), mitochondria (o), and endoplasmic reticulum (s). Oxidized Trxs are reduced by either ferredoxin, in a reaction catalyzed by ferredoxin-thioredoxin reductase (FTR) in the plastids, or by NADPH, in a reaction catalyzed by NADPH-thioredoxin reductase (NTRA and NTRB) in the cytosol and mitochondria. An additional and peculiar isoform (NTRC), found in the chloroplasts, contains NTR and Trx domains in the same polypeptide and is able to reduce peroxiredoxins without the assistance of classical Trxs. In this work, the Trx and NTR genes of Lotus japonicus have been identified and characterized by screening EST and genomic sequences, determining mRNA levels in plant tissues, and performing immunoblot and proteomic analyses. In L. japonicus, a model species for molecular studies of the rhizobia-legume symbiosis, the Trx gene family comprises at least fourteen members encoding six isoforms of Trxh, three isoforms of Trxm, and one isoform each of Trxf, Trxx, Trxy, Trxz and Trxo. However, we failed to detect any homologs of Trxs, a novel type of Trx dedicated to nitrogen-fixing symbiosis reported in Medicago truncatula3. Expression of Trxh1 was similarly high in roots, nodules and leaves, whereas expression of Trxh4 was higher in nodules than in roots and leaves. As expected, the Trxf, Trxm and Trxx genes, which encode plastidic isoforms, showed higher expression in leaves than in roots or nodules. In contrast, Trxo was uniformly expressed in the three plant organs. Proteomic analyses confirmed the presence of the Trxh1 protein in nodules. Similarly, we identified three NTR and one FTR genes that are expressed in roots, nodules and leaves, although the mRNA levels of NTRA were considerably greater than those of NTRB and NTRC. The expression of NTRC was much higher in the leaves. As occurs in Arabidopsis4, the NTRA and NTRB genes can generate two types of transcripts, encoding cytosolic and mitochondrial isoforms. These findings strongly support that cytosolic, mitochondrial, and plastidic NTRTrx redox systems are functional in legume root nodules.
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