title: PTOX Mediates Novel Pathways of Electron Transport in Etioplasts of Arabidopsis.
abstract: The immutans (im) variegation mutant of Arabidopsis defines the gene for PTOX (plastid terminal oxidase), a versatile plastoquinol oxidase in chloroplast membranes. In this report we used im to gain insight into the function of PTOX in etioplasts of dark-grown seedlings. We discovered that PTOX helps control the redox state of the plastoquinone (PQ) pool in these organelles, and that it plays an essential role in etioplast metabolism by participating in the desaturation reactions of carotenogenesis and in one or more redox pathways mediated by PGR5 (PROTON GRADIENT REGULATION 5) and NDH (NAD(P)H dehydrogenase), both of which are central players in cyclic electron transport. We propose that these elements couple PTOX with electron flow from NAD(P)H to oxygen, and by analogy to chlororespiration (in chloroplasts) and chromorespiration (in chromoplasts), we suggest that they define a respiratory process in etioplasts that we have termed "etiorespiration". We further show that the redox state of the PQ pool in etioplasts might control chlorophyll biosynthesis, perhaps by participating in mechanisms of retrograde (plastid-to-nucleus) signaling that coordinate biosynthetic and photoprotective activities required to poise the etioplast for light development. We conclude that PTOX is an important component of metabolism and redox sensing in etioplasts.
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, 445 Bessey Hall, Ames, IA 50011, USA.
authors.forename: Sekhar
authors.initials: S
authors.lastname: Kambakam
authors.affiliation: Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
authors.forename: Ujjal
authors.initials: U
authors.lastname: Bhattacharjee
authors.affiliation: Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Petrich
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, 445 Bessey Hall, Ames, IA 50011, USA. Electronic address: rodermel@iastate.edu.
authors.forename: Steve
authors.initials: S
authors.lastname: Rodermel
mesh_terms: D017360:Arabidopsis / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism / Q000502:physiology; D004579:Electron Transport / Q000502:physiology; D010084:Oxidation-Reduction; D010971:Plastoquinone / Q000031:analogs & derivatives / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D002338:Carotenoids; C003165:plastoquinol; C100185:(all-E) phytoene; D010971:Plastoquinone
keywords: PTOX; etiorespiration; immutans; phytoene; prochlorophyllide; retrograde singnaling