title: Alternative oxidases (AOX1a and AOX2) can functionally substitute for plastid terminal oxidase in Arabidopsis chloroplasts.
abstract: The immutans (im) variegation mutant of Arabidopsis thaliana is caused by an absence of PTOX, a plastid terminal oxidase bearing similarity to mitochondrial alternative oxidase (AOX). In an activation tagging screen for suppressors of im, we identified one suppression line caused by overexpression of AOX2. AOX2 rescued the im defect by replacing the activity of PTOX in the desaturation steps of carotenogenesis. Similar results were obtained when AOX1a was reengineered to target the plastid. Chloroplast-localized AOX2 formed monomers and dimers, reminiscent of AOX regulation in mitochondria. Both AOX2 and AOX1a were present in higher molecular weight complexes in plastid membranes. The presence of these proteins did not generally affect steady state photosynthesis, aside from causing enhanced nonphotochemical quenching in both lines. Because AOX2 was imported into chloroplasts using its own transpeptide, we propose that AOX2 is able to function in chloroplasts to supplement PTOX activity during early events in chloroplast biogenesis. We conclude that the ability of AOX1a and AOX2 to substitute for PTOX in the correct physiological and developmental contexts is a striking example of the capacity of a mitochondrial protein to replace the function of a chloroplast protein and illustrates the plasticity of the photosynthetic apparatus.
authors.affiliation: Department of Genetics, Development, and Cell Biology, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Aigen
authors.initials: A
authors.lastname: Fu
authors.forename: Huiying
authors.initials: H
authors.lastname: Liu
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.forename: Sekhar
authors.initials: S
authors.lastname: Kambakam
authors.forename: Sheng
authors.initials: S
authors.lastname: Luan
authors.forename: Steve
authors.initials: S
authors.lastname: Rodermel
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002338:Carotenoids / Q000096:biosynthesis; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation; D057075:Enzyme Assays; D005091:Exons / Q000235:genetics; D005453:Fluorescence; D016153:Genes, Suppressor; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D018087:Plastids / Q000201:enzymology*; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000201:enzymology; D013489:Suppression, Genetic; D000099188:Alternative Oxidase
chemical_list: D029681:Arabidopsis Proteins; D002338:Carotenoids; D002734:Chlorophyll; D000077194:Chlorophyll A; D049452:Green Fluorescent Proteins; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D000099188:Alternative Oxidase; C405742:IM protein, Arabidopsis