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.


Available from: Michael Melzer, Sep 15, 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: Iron is an essential element for plant growth and development, playing important roles in a variety of cellular activities including cell respiration, chlorophyll biosynthesis, and DNA synthesis. In chloroplasts, iron is essential for photosynthetic electron transport and functions as a cofactor for superoxide dismutases. Thus, iron homeostasis is critical for chloroplast and plant development. To better understand the mechanisms by which iron is transported into chloroplasts, we cloned and characterized the Nicotiana tabacum homolog of AtPIC1, which is a chloroplast iron transporter in Arabidopsis thaliana. NtPIC1 was expressed in many tissues of the tobacco plant, and the encoded protein was localized to the chloroplast envelope. Southern blotting indicated that there is a single copy of NtPIC1 in the tobacco genome. Moreover, yeast complementation assays suggested that NtPIC1 transports iron. We used RNA interference to downregulate NtPIC1 in transgenic plants, which resulted in albinism, dwarfism, iron-deficient chloroplasts, and chloroplast that exhibited ultrastructural defects. NtPIC1 overexpression resulted in deep-green leaves, elevated levels of chlorophyll, more densely packed chloroplasts, and the accumulation of iron and starch grains within chloroplasts. In addition, NtPIC1 influenced the expression of genes involved in iron transport, iron storage, iron oxidative stress, and the biogenesis of iron-sulfur proteins. These results suggest that NtPIC1 transports iron into chloroplasts, regulates iron homeostasis, and influences plant development.
    Plant Molecular Biology Reporter 06/2014; 33(3). DOI:10.1007/s11105-014-0758-5 · 2.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This chapter is intended as a background on natural photosynthesis for those interested in artificial photosynthesis. It describes how light is used for creating positive and negative charges, and how these charges are transferred through the molecular assemblies in the membranes. Next, the chapter also describes how the charge transport leads to creation of a pH difference across the photosynthetic membrane, and how charge and pH differences lead to the production of high-energy phosphate that can be used in chemical synthesis. The chapter overviews photophosphorylation in chromatophores of photosynthetic bacteria and, discusses carbon dioxide assimilation systems in oxygenic organisms. Finally, it describes how the type of photosynthesis present today has evolved over billions of years, and what can we expect of the future that we are ourselves able to influence. In addition, in the end, the chapter considers some interesting photosynthesis-related questions relevant to whole land and aquatic plants.
    Natural and Artificial Photosynthesis: Solar Power as an Energy Source, Edited by R. Razeghifard, 09/2013: chapter Oxygenic Photosynthesis: pages 13-63; John Wiley & Sons Inc.., ISBN: 9781118160060
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Reactive oxygen species (ROS) produced by plants in adverse environments can cause damage to organelles and trigger cell death. Removal of excess ROS can be achieved through the ascorbate scavenger pathway to prevent plant cell death. The amount of this scavenger can be regulated by ferredoxin (FDX). Chloroplastic FDXs are electron transfer proteins that perform in distributing photosynthetic reducing power. In this study, we demonstrate that overexpression of the endogenous photosynthetic FDX gene, PETF, in Chlamydomonas reinhardtii could raise the level of reduced ascorbate and diminish H2O2 levels under normal growth conditions. Furthermore, the overexpressing PETF transgenic Chlamydomonas lines produced low levels of H2O2 and exhibited protective effects that were observed through decreased chlorophyll degradation and increased cell survival under heat-stress conditions. The findings of this study suggest that overexpression of PETF can increase the efficiency of ROS scavenging in chloroplasts to confer heat tolerance. The roles of PETF in the downregulation of the ROS level offer a method for potentially improving the tolerance of crops against heat stress.
    International Journal of Molecular Sciences 10/2013; 14(10):20913-29. DOI:10.3390/ijms141020913 · 2.34 Impact Factor