title: Superoxide generated from the glutathione-mediated reduction of selenite damages the iron-sulfur cluster of chloroplastic ferredoxin.
abstract: Selenium assimilation in plants is facilitated by several enzymes that participate in the transport and assimilation of sulfate. Manipulation of genes that function in sulfur metabolism dramatically affects selenium toxicity and accumulation. However, it has been proposed that selenite is not reduced by sulfite reductase. Instead, selenite can be non-enzymatically reduced by glutathione, generating selenodiglutathione and superoxide. The damaging effects of superoxide on iron-sulfur clusters in cytosolic and mitochondrial proteins are well known. However, it is unknown if superoxide damages chloroplastic iron-sulfur proteins. The goals of this study were twofold: to determine whether decreased activity of sulfite reductase impacts selenium tolerance in Arabidopsis, and to determine if superoxide generated from the glutathione-mediated reduction of selenite damages the iron-sulfur cluster of ferredoxin. Our data demonstrate that knockdown of sulfite reductase in Arabidopsis does not affect selenite tolerance or selenium accumulation. Additionally, we provide in vitro evidence that the non-enzymatic reduction of selenite damages the iron-sulfur cluster of ferredoxin, a plastidial protein that is an essential component of the photosynthetic light reactions. Damage to ferredoxin's iron-sulfur cluster was associated with formation of apo-ferredoxin and impaired activity. We conclude that if superoxide damages iron-sulfur clusters of ferredoxin in planta, then it might contribute to photosynthetic impairment often associated with abiotic stress, including toxic levels of selenium.
authors.affiliation: Coastal Carolina University, Biology Department, Conway, SC, 29526, USA. Electronic address: bjfisher@g.coastal.edu.
authors.forename: Brian
authors.initials: B
authors.lastname: Fisher
authors.affiliation: Ben-Gurion University, Blaustein Institutes for Desert Research, Beer Sheva, Israel. Electronic address: dmitry.yarmolinsky@ut.ee.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Yarmolinsky
authors.affiliation: Colorado State University, Biology Department, Fort Collins, CO, 80523, USA. Electronic address: salahghany@gmail.com.
authors.forename: Salah
authors.initials: S
authors.lastname: Abdel-Ghany
authors.affiliation: Colorado State University, Biology Department, Fort Collins, CO, 80523, USA. Electronic address: pilon@colostate.edu.
authors.forename: Marinus
authors.initials: M
authors.lastname: Pilon
authors.affiliation: Colorado State University, Biology Department, Fort Collins, CO, 80523, USA. Electronic address: epsmits@colostate.edu.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Pilon-Smits
authors.affiliation: Ben-Gurion University, Blaustein Institutes for Desert Research, Beer Sheva, Israel. Electronic address: gizi@bgu.ac.il.
authors.forename: Moshe
authors.initials: M
authors.lastname: Sagi
authors.affiliation: Coastal Carolina University, Biology Department, Conway, SC, 29526, USA. Electronic address: dougvh@coastal.edu.
authors.forename: Doug
authors.initials: D
authors.lastname: Van Hoewyk
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005287:Ferredoxin-NADP Reductase / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D005978:Glutathione / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D020887:Selenious Acid / Q000633:toxicity*; D013057:Spectrum Analysis; D050889:Sulfite Reductase (Ferredoxin); D013481:Superoxides / Q000378:metabolism*
chemical_list: D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D013481:Superoxides; D009249:NADP; D045304:Cytochromes c; D005287:Ferredoxin-NADP Reductase; D050889:Sulfite Reductase (Ferredoxin); D020887:Selenious Acid; D005978:Glutathione
keywords: Ferredoxin; Iron-sulfur cluster; Oxidative stress; Selenium; Superoxide