Theredox imbalancedMutants of Arabidopsis Differentiate Signaling Pathways for Redox Regulation of Chloroplast Antioxidant Enzymes

Abstract

A network of enzymatic and nonenzymatic antioxidants protects chloroplasts from photooxidative damage. With all enzymatic components being nuclear encoded, the control of the antioxidant capacity depends on chloroplast-to-nucleus redox signaling. Using an Arabidopsis (Arabidopsis thaliana) reporter gene line expressing luciferase under control of the redox-sensitive 2-cysteine peroxiredoxin A (2CPA) promoter, six mutants with low 2CPA promoter activity were isolated, of which five mutants show limitations in redox-box regulation of the 2CPA promoter. In addition to 2CPA, the transcript levels for other chloroplast antioxidant enzymes were decreased, although a higher oxidation status of the ascorbate pool, a higher reduction state of the plastoquinone pool, and an increased oxidation status of the 2-Cys peroxiredoxin pool demonstrated photooxidative stress conditions. Greening of the mutants, chloroplast ultrastructure, steady-state photosynthesis, and the responses to the stress hormone abscisic acid were wild type like. In the rosette state, the mutants were more sensitive to low CO 2 and to hydrogen peroxide. Comparison of gene expression patterns and stress sensitivity characterizes the mutants as redox imbalanced in the regulation of nuclear-encoded chloroplast antioxidant enzymes and differentiates redox signaling cascades.

Chloroplast NADPH-Thioredoxin Reductase Interacts with Photoperiodic Development in Arabidopsis

“…In fact, substantial increase in the accumulation of hydrogen peroxide in ntrc leaves was reported to occur solely upon reillumination of plants after a prolonged 3-d dark treatment (Perez-Ruiz et al, 2006). It is also worth noting that the mutants with lower contents of chloroplast 2-Cys peroxiredoxins showed stronger phenotypes under long-day than under short-day growth conditions and that the stress symptoms became more severe in older plants (Heiber et al, 2007). Yet, the ntrc phenotype showed the opposite trend.…”

Peroxiredoxins in Plants and Cyanobacteria

“…Regulation of 1-CysPrx, which involves ABA-responsive elements and ABI3 and ABI5, has been described above in the paragraph on developmental control of gene expression. As to the latter example, 2-CysPrx has served as model to study redoxdependent retrograde signaling from the chloroplast to the nucleus (10,56,60,161). The promoter of At-2-CysPrxA drives b-glucuronidase expression in transgenic A. thaliana in dependence on the electron pressure downstream of photosystem I.…”

“…Two subsequent studies employed the redox sensitive promoter of At-2-CysPrxA (p2CPA) to advance the understanding on the mechanism of redox control of At-2-CysPrx expression. LUC reporter gene was expressed in transgenic A. thaliana under control of the 2184-bp promoter fragment of p2CPA (56). The lines were chemically mutagenized and screened for mutants with constitutively underexpressed 2-CysPrx.…”

“…Obtained independent mutant lines display disturbed redox balance (rimb mutants: redox imbalance), increased oxidation state of ascorbate, higher reduction of plastoquinone pool, increased oxidation of 2-CysPrx, and alterations in other redox-related traits. The identification of the mutations triggering the constitutive downregulation of 2-CysPrx expression despite increased oxidative stress are expected to shed light on signaling pathways that control 2-CysPrx expression (56). In a yeast-1-hybrid screen the transcription factor RAP2.4a was identified and confirmed as binding partner and regulator of the redox box of the At-2-CysPrxA promoter (161).…”

Friend or Foe? Exploring the Factors that Determine the Difference Between Positive and Negative Effects on Photosynthesis in Response to Insect Herbivory

“…Another nebulous aspect of the model is the mechanism by which H 2 O 2 , produced in multiple cell sites and in response to various different stresses and stimuli, acquires the specificity needed to act as a reliable signal conveying information on the state of chloroplasts to the nucleus. Further experimental support for the presence of independent redox signaling pathways acting via differentiated signaling cascades came from the characterization of the so called www.intechopen.com redox-imbalanced (rimb) mutants, which were detected using an Arabidopsis reporter gene line expressing luciferase under control of the redox-sensitive 2-cysteine peroxiredoxin A (2CPA) promoter (Heiber et al, 2007). Valuable information shedding light on the nature of redox signaling should be expected when the identity of the RIMB genes and their biochemical function is determined.…”