title: Two alanine aminotranferases link mitochondrial glycolate oxidation to the major photorespiratory pathway in Arabidopsis and rice.
abstract: The major photorespiratory pathway in higher plants is distributed over chloroplasts, mitochondria, and peroxisomes. In this pathway, glycolate oxidation takes place in peroxisomes. It was previously suggested that a mitochondrial glycolate dehydrogenase (GlcDH) that was conserved from green algae lacking leaf-type peroxisomes contributes to photorespiration in Arabidopsis thaliana. Here, the identification of two Arabidopsis mitochondrial alanine:glyoxylate aminotransferases (ALAATs) that link glycolate oxidation to glycine formation are described. By this reaction, the mitochondrial side pathway produces glycine from glyoxylate that can be used in the glycine decarboxylase (GCD) reaction of the major pathway. RNA interference (RNAi) suppression of mitochondrial ALAAT did not result in major changes in metabolite pools under standard conditions or enhanced photorespiratroy flux, respectively. However, RNAi lines showed reduced photorespiratory CO(2) release and a lower CO(2) compensation point. Mitochondria isolated from RNAi lines are incapable of converting glycolate to CO(2), whereas simultaneous overexpression of GlcDH and ALAATs in transiently transformed tobacco leaves enhances glycolate conversion. Furthermore, analyses of rice mitochondria suggest that the side pathway for glycolate oxidation and glycine formation is conserved in monocotyledoneous plants. It is concluded that the photorespiratory pathway from green algae has been functionally conserved in higher plants.
authors.affiliation: Leibniz University Hannover, Institute of Botany, D-30419 Hannover, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Niessen
authors.forename: Katrin
authors.initials: K
authors.lastname: Krause
authors.forename: Ina
authors.initials: I
authors.lastname: Horst
authors.forename: Norma
authors.initials: N
authors.lastname: Staebler
authors.forename: Stephanie
authors.initials: S
authors.lastname: Klaus
authors.forename: Stefanie
authors.initials: S
authors.lastname: Gaertner
authors.forename: Rashad
authors.initials: R
authors.lastname: Kebeish
authors.forename: Wagner L
authors.initials: WL
authors.lastname: Araujo
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
authors.forename: Christoph
authors.initials: C
authors.lastname: Peterhansel
mesh_terms: D000410:Alanine Transaminase / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D006016:Glycolates / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D006016:Glycolates; D010940:Plant Proteins; C031149:glycolic acid; D002245:Carbon Dioxide; D010088:Oxidoreductases; D000410:Alanine Transaminase; D005998:Glycine