title: Induction of the AOX1D isoform of alternative oxidase in A. thaliana T-DNA insertion lines lacking isoform AOX1A is insufficient to optimize photosynthesis when treated with antimycin A.
abstract: Plant respiration is characterized by two pathways for electron transfer to O(2), namely the cytochrome pathway (CP) that is linked to ATP production, and the alternative pathway (AP), where electrons from ubiquinol are directly transferred to O(2) via an alternative oxidase (AOX) without concomitant ATP production. This latter pathway is well suited to dispose of excess electrons in the light, leading to optimized photosynthetic performance. We have characterized T-DNA-insertion mutant lines of Arabidopsis thaliana that do not express the major isoform, AOX1A. In standard growth conditions, these plants did not show any phenotype, but restriction of electron flow through CP by antimycin A, which induces AOX1A expression in the wild-type, led to an increased expression of AOX1D in leaves of the aox1a-knockout mutant. Despite the increased presence of the AOX1D isoform in the mutant, antimycin A caused inhibition of photosynthesis, increased ROS, and ultimately resulted in amplified membrane leakage and necrosis when compared to the wild-type, which was only marginally affected by the inhibitor. It thus appears that AOX1D was unable to fully compensate for the loss of AOX1A when electron flow via the CP is restricted. A combination of inhibition studies, coupled to metabolite profiling and targeted expression analysis of the P-protein of glycine decarboxylase complex (GDC), suggests that the aox1a mutants attempt to increase their capacity for photorespiration. However, given their deficiency, it is intriguing that increase in expression neither of AOX1D nor of GDC could fully compensate for the lack of AOX1A to optimize photosynthesis when treated with antimycin A. We suggest that the aox1a mutants can further be used to substantiate the current models concerning the influence of mitochondrial redox on photosynthetic performance and gene expression.
authors.affiliation: Department of Plant Physiology, FB5, University of Osnabrueck, 49069 Osnabrueck, Germany.
authors.forename: Inga
authors.initials: I
authors.lastname: Strodtkötter
authors.forename: Kollipara
authors.initials: K
authors.lastname: Padmasree
authors.forename: Challabathula
authors.initials: C
authors.lastname: Dinakar
authors.forename: Birgit
authors.initials: B
authors.lastname: Speth
authors.forename: Pamela S
authors.initials: PS
authors.lastname: Niazi
authors.forename: Joanna
authors.initials: J
authors.lastname: Wojtera
authors.forename: Ingo
authors.initials: I
authors.lastname: Voss
authors.forename: Phuc Thi
authors.initials: PT
authors.lastname: Do
authors.forename: Adriano
authors.initials: A
authors.lastname: Nunes-Nesi
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
authors.forename: Vera
authors.initials: V
authors.lastname: Linke
authors.forename: Agepati S
authors.initials: AS
authors.lastname: Raghavendra
authors.forename: Renate
authors.initials: R
authors.lastname: Scheibe
mesh_terms: D000968:Antimycin A / Q000494:pharmacology*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D017931:DNA Primers; D004269:DNA, Bacterial; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D024101:Mitochondrial Proteins; D010088:Oxidoreductases / Q000096:biosynthesis* / Q000235:genetics; D010788:Photosynthesis / Q000187:drug effects*; D010940:Plant Proteins; D012333:RNA, Messenger / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099188:Alternative Oxidase
chemical_list: D000968:Antimycin A; D017931:DNA Primers; D004269:DNA, Bacterial; D007527:Isoenzymes; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D000099188:Alternative Oxidase; C036483:T-DNA