Abstract
Chloroplast NADPH-thioredoxin reductase (NTRC) belongs to the thioredoxin systems that control crucial metabolic and regulatory pathways in plants. Here, by characterization of T-DNA insertion lines of NTRC gene, we uncover a novel connection between chloroplast thiol redox regulation and the control of photoperiodic growth in Arabidopsis (Arabidopsis thaliana). Transcript and metabolite profiling revealed severe developmental and metabolic defects in ntrc plants grown under a short 8-h light period. Besides reduced chlorophyll and anthocyanin contents, ntrc plants showed alterations in the levels of amino acids and auxin. Furthermore, a low carbon assimilation rate of ntrc leaves was associated with enhanced transpiration and photorespiration. All of these characteristics of ntrc were less severe when plants were grown under a long 16-h photoperiod. Transcript profiling revealed that the mutant phenotypes of ntrc were accompanied by differential expression of genes involved in stomatal development, chlorophyll biosynthesis, chloroplast biogenesis, and circadian clock-linked light perception systems in ntrc plants. We propose that NTRC regulates several key processes, including chlorophyll biosynthesis and the shikimate pathway, in chloroplasts. In the absence of NTRC, imbalanced metabolic activities presumably modulate the chloroplast retrograde signals, leading to altered expression of nuclear genes and, ultimately, to the formation of the pleiotrophic phenotypes in ntrc mutant plants.
Highlights
Chloroplast NADPH-thioredoxin reductase (NTRC) belongs to the thioredoxin systems that control crucial metabolic and regulatory pathways in plants
Plants possess two main types of thioredoxin reductases, the universal NADPH-dependent thioredoxin reductase (NTR) and the plastidial ferredoxin-dependent thioredoxin reductase (FTR), which is unique for photosynthetic organisms (Hirt et al, 2002; Dai et al, 2004)
Functional analysis of the Arabidopsis single mutants ntra and ntrb revealed no phenotypic deficiencies under standard growth conditions (Reichheld et al, 2007)
Summary
Chloroplast NADPH-thioredoxin reductase (NTRC) belongs to the thioredoxin systems that control crucial metabolic and regulatory pathways in plants. Numerous studies have revealed crucial functions for thioredoxins in the regulation of developmental and acclimation processes in plants (for review, see Buchanan and Balmer, 2005), and the vital roles for thioredoxin superfamily members in oxidative stress responses have become evident (Hirt et al, 2002; Perez-Ruiz et al, 2006; Vieira Dos Santos and Rey, 2006). The Arabidopsis NTRC gene encodes a chloroplast-localized NTR that comprises a unique isoform found in oxygenic photosynthetic organisms and in Mycobacterium leprae (Hirt et al, 2002; Serrato et al, 2004; Perez-Ruiz et al, 2006). Besides the conserved NTR domain, NTRC possesses an additional thioredoxin domain at the C terminus of the protein (Serrato et al, 2004)
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