Article

Cyanobacterial flavodoxin complements ferredoxin deficiency in knocked-down transgenic tobacco plants.

División Biología Molecular, Facultad de Ciencias Bioquímicas y Farmacéuticas, Instituto de Biología Molecular y Celular de Rosario (IBR, CONICET), Universidad Nacional de Rosario, S2002LRK Rosario, Argentina.
The Plant Journal (Impact Factor: 6.58). 12/2010; 65(6):922-35. DOI: 10.1111/j.1365-313X.2010.04479.x
Source: PubMed

ABSTRACT Ferredoxins are the main electron shuttles in chloroplasts, accepting electrons from photosystem I and delivering them to essential oxido-reductive pathways in the stroma. Ferredoxin levels decrease under adverse environmental conditions in both plants and photosynthetic micro-organisms. In cyanobacteria and some algae, this decrease is compensated for by induction of flavodoxin, an isofunctional flavoprotein that can replace ferredoxin in many reactions. Flavodoxin is not present in plants, but tobacco lines expressing a plastid-targeted cyanobacterial flavodoxin developed increased tolerance to environmental stress. Chloroplast-located flavodoxin interacts productively with endogenous ferredoxin-dependent pathways, suggesting that its protective role results from replacement of stress-labile ferredoxin. We tested this hypothesis by using RNA antisense and interference techniques to decrease ferredoxin levels in transgenic tobacco. Ferredoxin-deficient lines showed growth arrest, leaf chlorosis and decreased CO(2) assimilation. Chlorophyll fluorescence measurements indicated impaired photochemistry, over-reduction of the photosynthetic electron transport chain and enhanced non-photochemical quenching. Expression of flavodoxin from the nuclear or plastid genome restored growth, pigment contents and photosynthetic capacity, and relieved the electron pressure on the electron transport chain. Tolerance to oxidative stress also recovered. In the absence of flavodoxin, ferredoxin could not be decreased below 45% of physiological content without fatally compromising plant survival, but in its presence, lines with only 12% remaining ferredoxin could grow autotrophically, with almost wild-type phenotypes. The results indicate that the stress tolerance conferred by flavodoxin expression in plants stems largely from functional complementation of endogenous ferredoxin by the cyanobacterial flavoprotein.

0 Bookmarks
 · 
69 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Salinity is one of the major environmental limiting factors that affects growth and productivity of rice (Oryza sativa L.) worldwide. Rice is among the most sensitive crops to salinity, especially at early vegetative stages. In order to get a better understanding of molecular pathways affected in rice mutants showing contrasting responses to salinity, we exploited the power of 2-DE based proteomics to explore the proteome changes associated with salt stress response. Our physiological observations showed that standard evaluation system (SES) scores, Na(+) and K(+) concentrations in shoots and Na(+)/K(+) ratio were significantly different in contrasting mutants under salt stress condition. Proteomics analysis showed that, out of 854 protein spots which were reproducibly detected, 67 protein spots showed significant responses to salt stress. The tandem mass spectrometry analysis of these significantly differentially accumulated proteins resulted in identification of 34 unique proteins. These proteins are involved in various molecular processes including defense to oxidative stresses, metabolisms, photosynthesis, protein synthesis and processing, signal transduction. Several of the identified proteins were emerged as key participants in salt stress tolerance. The possible implication of salt responsive proteins in plant adaptation to salt stress is discussed.
    Journal of plant physiology 10/2013; · 2.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: AIM: To determine whether expression of a cyanobacterial flavodoxin in soil bacteria of agronomic interest confers protection against the widely used herbicides paraquat and atrazine. METHODS AND RESULTS: The model bacterium Escherichia coli, the symbiotic nitrogen-fixing bacterium Ensifer meliloti and the plant growth-promoting rhizobacterium Pseudomonas fluorescens Aur6 were transformed with expression vectors containing the flavodoxin gene of Anabaena variabilis. Expression of the cyanobacterial protein was confirmed by Western blot. Bacterial tolerance to oxidative stress was tested in solid medium supplemented with hydrogen peroxide, paraquat or atrazine. In all three bacterial strains, flavodoxin expression enhanced tolerance to the oxidative stress provoked by hydrogen peroxide and by the ROS-inducing herbicides, witnessed by the enhanced survival of the transformed bacteria in the presence of these oxidizing agents. CONCLUSIONS: Flavodoxin overexpression in beneficial soil bacteria confers tolerance to oxidative stress and improves their survival in the presence of the herbicides paraquat and atrazine. Flavodoxin could be considered as a general antioxidant resource to face oxidative challenges in different microorganisms. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of plant growth-promoting rhizobacteria or nitrogen-fixing bacteria with enhanced tolerance to oxidative stress in contaminated soils is of significant agronomic interest. The enhanced tolerance of flavodoxin-expressing bacteria to atrazine and paraquat points to potential applications in herbicide-treated soils. This article is protected by copyright. All rights reserved.
    Journal of Applied Microbiology 04/2013; · 2.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Photosynthetic electron transport is the major energy source for cellular metabolism in plants, and it also has the potential to generate excess reactive oxygen species that cause irreversible damage to photosynthetic apparatus under adversities. Ferredoxins (Fds), as the electron distributing hub in the chloroplast, contribute to redox regulation and antioxidant defenses. However, the steady state levels of photosynthetic Fd decline in plants when they are exposed to environmental stress conditions. To understand the effect of Fd downregulation on plant growth, we characterized the plants lacking Fd2 (Fd2-KO) in Arabidopsis thaliana under long-term high light (HL) conditions. Unexpectedly, Fd2-KO plants exhibited efficient photosynthetic capacity and stable thylakoid protein complexes. At the transcriptional level, photoprotection-related genes were upregulated more in the mutant plants, suggesting that knockout Fd2 lines possess a relatively effective photoacclimatory responses involving enhanced plastid redox signaling. Contrary to the physiological characterization of Fd2-KO under short-term HL, during extended HL the PQ pool returned to a relatively balanced redox state via elevated PGR5-dependent cyclic electron flow. fd2pgr5 double mutant plants displayed severely impaired photosynthetic capacity under HL treatment, further supporting a role for PGR5 in adaptation to HL in the Fd2-KO plants. These results suggest potential benefits in reducing Fd levels in plants grown under long-term HL conditions. This article is protected by copyright. All rights reserved.
    The Plant Journal 10/2013; · 6.58 Impact Factor

Full-text

View
0 Downloads