title: Environmental selection pressures related to iron utilization are involved in the loss of the flavodoxin gene from the plant genome.
abstract: Oxidative stress and iron limitation represent the grim side of life in an oxygen-rich atmosphere. The versatile electron transfer shuttle ferredoxin, an iron-sulfur protein, is particularly sensitive to these hardships, and its downregulation under adverse conditions severely compromises survival of phototrophs. Replacement of ferredoxin by a stress-resistant isofunctional carrier, flavin-containing flavodoxin, is a widespread strategy employed by photosynthetic microorganisms to overcome environmental adversities. The flavodoxin gene was lost in the course of plant evolution, but its reintroduction in transgenic plants confers increased tolerance to environmental stress and iron starvation, raising the question as to why a genetic asset with obvious adaptive value was not kept by natural selection. Phylogenetic analyses reveal that the evolutionary history of flavodoxin is intricate, with several horizontal gene transfer events between distant organisms, including Eukarya, Bacteria, and Archaea. The flavodoxin gene is unevenly distributed in most algal lineages, with flavodoxin-containing species being overrepresented in iron-limited regions and scarce or absent in iron-rich environments. Evaluation of cyanobacterial genomic and metagenomic data yielded essentially the same results, indicating that there was little selection pressure to retain flavodoxin in iron-rich coastal/freshwater phototrophs. Our results show a highly dynamic evolution pattern of flavodoxin tightly connected to the bioavailability of iron. Evidence presented here also indicates that the high concentration of iron in coastal and freshwater habitats may have facilitated the loss of flavodoxin in the freshwater ancestor of modern plants during the transition of photosynthetic organisms from the open oceans to the firm land.
authors: Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET-Universidad Nacional de Rosario, Ocampo y Esmeralda, Rosario, Argentina.
authors: Juan J
authors: JJ
authors: Pierella Karlusich
authors: Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET-Universidad Nacional de Rosario, Ocampo y Esmeralda, Rosario, Argentina Present address: Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario; CONICET, Rosario, Argentina.
authors: Romina D
authors: RD
authors: Ceccoli
authors: Unidad de Bioinformática, Institut Pasteur Montevideo, Uruguay.
authors: Martín
authors: M
authors: Graña
authors: Departamento de Ecología y Evolución, Facultad de Ciencias/CURE, Universidad de la República, Montevideo, Uruguay eletor@fcien.edu.uy carrillo@ibr-conicet.gov.ar.
authors: Héctor
authors: H
authors: Romero
authors: Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET-Universidad Nacional de Rosario, Ocampo y Esmeralda, Rosario, Argentina eletor@fcien.edu.uy carrillo@ibr-conicet.gov.ar.
authors: Néstor
authors: N
authors: Carrillo
mesh_terms: D000458:Cyanobacteria / Q000235:genetics; D004777:Environment; D019143:Evolution, Molecular; D005418:Flavodoxin / Q000145:classification / Q000235:genetics*; D017343:Genes, Plant; D018745:Genome, Plant; D007501:Iron / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000235:genetics; D052817:Phototrophic Processes / Q000235:genetics; D010802:Phylogeny
chemical_list: D005418:Flavodoxin; D045332:Photosystem II Protein Complex; C054266:photosystem II manganese-stabilizing protein; D007501:Iron
keywords: algae; cyanobacteria; ferredoxin; flavodoxin; iron; photosynthesis