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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: 6.82). 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.

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    • "Flds can be used as biotechnological tools to engineer tolerance to oxidative stress. Transgenic tobacco plants that constitutively express a cyanobacterial Fld exhibit enhanced tolerance to a broad range of stresses that provoke oxidative damage (Tognetti et al. 2006, 2007a,b; Blanco et al. 2011; Ceccoli et al. 2011), while tolerance of nitrogen-fixing activity to salinity is enhanced in transgenic Medicago truncatula plants expressing Fld (Coba de la Pe~ na et al. 2010). Moreover, overexpression of flavodoxin in the heterotrophic bacterium Ensifer meliloti protects free-living bacteria against cadmium stress (Shvaleva et al. 2010), while expression of a heterologous Fld in symbiotic forms of E. meliloti ameliorates the oxidative balance, thus delaying natural nodule senescence (Redondo et al. 2009) and enhancing the tolerance of alfalfa nodules to cadmium (Shvaleva et al. 2010) and saline stress (Redondo et al. 2012). "
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    • "Flavodoxin can replace ferredoxin in the photosynthetic electron transport from photosystem I to NADP ? and in nitrogenase reduction (Sandmann et al. 1990). Blanco et al. (2011) have shown that cyanobacterial flavodoxin expression can complement ferredoxin deficiency in transgenic ferredoxindeficient tobacco lines. In alfalfa nodules, flavodoxin might increase effectiveness of the nitrogenase complex by compensating the ferredoxin decline that occurs under osmotic stress (Zimmermann et al. 2004; Tognetti et al. 2006). "
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    • "The decline in Fd amounts leads to overreduction of the PETC due to shortage of electron acceptors. Under such circumstances the electron surplus could be passed straight to oxygen resulting in ROS generation [39] [40] [41]. Iron–sulfur centers are vulnerable to ROS attack to various extents , depending on solvent exposure and the polypeptide environment surrounding the cluster. "
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