Unique properties of NADP-thioredoxin reductase C in legumes

Abstract

NADP-thioredoxin reductases (NTRs) reduce thioredoxins (Trxs), using NADPH as a reductant, together constituting complete redox systems (NTS). Beside NTRA and NTRB targeted to both cytosol and mitochondria of plant cells, there is in chloroplasts an unusual NTR (NTRC) harbouring a Trx domain in a C-terminal extension, as recently reported in Oryza sativa. Although NTRC may constitute a complete NTS, it was described as a bifunctional enzyme. Because the gene is only present in photosynthetic organisms and the protein in green tissues, NTRC was thought to have a role restricted to photosynthetic cells. To determine whether NTRC from dicot plants is a bifunctional enzyme or a complete NTS, as well as to identify its putative target, NTRC from Medicago truncatula was cloned and NTRA was cloned for comparison. Here evidence is presented that MtNTRC (i) acts as an NTS and reduces dithiobisnitrobenzoate (DTNB) with a turnover (0.62 s(-1)) similar to that measured with MtNTRA in the presence of a Trxh (0.81 s(-1)); (ii) is able to use both NADPH (k(M)=2.4 microM) and NADH (k(M)=11 microM) as cofactors; (iii) efficiently reduces BAS1, a plastidial peroxiredoxin; and (iv) is expressed in both leaves and stems but unexpectedly is even more abundant in cotyledons from dry and germinating seeds. Because BAS1 is also present in both green tissues and seeds, NTRC/BAS1 may be involved in the scavenging of peroxides produced in green tissues during the day or the night and in seeds during germination. These results suggest different roles for NTRC in monocot and dicot plants.

NADPH Thioredoxin Reductase C Is Localized in Plastids of Photosynthetic and Nonphotosynthetic Tissues and Is Involved in Lateral Root Formation in Arabidopsis

“…Moreover, the analysis of these plants revealed a more unexpected expression in tissues of reproductive organs, such as stigma and anthers. Therefore, although NTRC is expressed at high levels in photosynthetic tissues, in agreement with previous reports (Serrato et al, 2004;Moon et al, 2006;Alkhalfioui et al, 2007;Lepistö et al, 2009), the different approaches performed in this work reveal a broad pattern of expression in either photosynthetic and nonphotosynthetic tissues for this gene.…”

A Novel Type of Thioredoxin Dedicated to Symbiosis in Legumes

“…M. truncatula NTRA (MtNTRA; Alkhalfioui et al, 2007) was chosen for these experiments, because it had previously been shown that NTRs of the A/B Figure 1. Darwin tree of M. truncatula and Arabidopsis Trx protein sequences.…”

“…Trx activity was measured using the insulin or DTNB reduction assays as previously described (Holmgren, 1979;Jacquot et al, 1995) using either DTT or NADPH plus recombinant MtNTRA (Alkhalfioui et al, 2007) as a reductant.…”

NADPH Thioredoxin Reductase C and Thioredoxins Act Concertedly in Seedling Development

“…NTRC is exclusive of organisms that perform oxygenic photosynthesis and shows plastid localization in plants (Kirchsteiger et al, 2012). Moreover, biochemical analyses revealed that NTRC is able to conjugate both NTR and Trx activities to efficiently reduce the hydrogen peroxide-scavenging enzyme 2-Cys peroxiredoxin (Moon et al, 2006;Pérez-Ruiz et al, 2006;Alkhalfioui et al, 2007). Arabidopsis (Arabidopsis thaliana) NTRC knockout mutants show a characteristic phenotype of retarded growth and pale green leaves, this phenotype being more severe under shortday conditions (Pérez-Ruiz et al, 2006;Lepistö et al, 2009).…”