Ornithine-δ-aminotransferase is essential for Arginine Catabolism but not for Proline Biosynthesis

By D. Funck, Bettina Stadelhofer, Wolfgang Koch. BMC Plant Biology, 2008

208 citations recorded by the source corpus.

BackgroundLike many other plant species, Arabidopsis uses arginine (Arg) as a storage and transport form of nitrogen, and proline (Pro) as a compatible solute in the defence against abiotic stresses causing water deprivation. Arg catabolism produces ornithine (Orn) inside mitochondria, which was discussed controversially as a precursor for Pro biosynthesis, alternative to glutamate (Glu).ResultsWe show here that ornithine-δ-aminotransferase (δOAT, At5g46180), the enzyme converting Orn to pyrroline-5-carboxylate (P5C), is localised in mitochondria and is essential for Arg catabolism. Wildtype plants could readily catabolise supplied Arg and Orn and were able to use these amino acids as the only nitrogen source. Deletion mutants of δOAT, however, accumulated urea cycle intermediates when fed with Arg or Orn and were not able to utilize nitrogen provided as Arg or Orn. Utilisation of urea and stress induced Pro accumulation were not affected in T-DNA insertion mutants with a complete loss of δOAT expression.ConclusionOur findings indicate that δOAT feeds P5C exclusively into the catabolic branch of Pro metabolism, which yields Glu as an end product. Conversion of Orn to Glu is an essential route for recovery of nitrogen stored or transported as Arg. Pro biosynthesis occurs predominantly or exclusively via the Glu pathway in Arabidopsis and does not depend on Glu produced by Arg and Orn catabolism.

Subfields: Molecular Biology, Plant Science

View Paper: https://www.semanticscholar.org/paper/e215bf7556107bb2420b3a57ca89fdf096bd35b9

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Citations in the corpus

Proline Mechanisms of Stress Survival (2013, background): “Glutamate appears to be the main precursor in stressinduced proline accumulation in plants, as the ornithine pathway mainly facilitates nitrogen recycling from arginine to glutamate (41, 123).”
Proline: a key player in plant abiotic stress tolerance (2015, background): “Abbreviations: ABA - abscisic acid; APX - ascorbate peroxidase; CAT - catalase; GR - glutathione reductase; GSA - glutamate semialdehyde; H2O2 - hydrogen peroxide; O2- - superoxide; OH• - hydroxyl radical; OAT - ornithine aminotransferase; PPP - pentose phosphate pathway; P5C - pyrroline-5-carboxyla”
Amino Acid Catabolism in Plants. (2015, background): “…degradation of arginine proceeds by transamination of ornithine to 1-pyrroline-5-carboxylate (P5C; reaction 7) and subsequent oxidation to glutamate via glutamic semialdehyde by NAD(P)+dependent 1-pyrroline-5-carboxylate dehydrogenase (reaction 9) in the mitochondrial matrix (Funck et al., 2008).”
Metabolic and molecular-genetic regulation of proline signaling and itscross-talk with major effectors mediates abiotic stress tolerance in plants (2015, background): “This prevents the direct utilization of the δOAT-generated P5C by P5CR, due to the localization of the latter in the cytosol or plastids (Funck et al., 2008).”
Proline Metabolism and Its Implications for Plant-Environment Interaction (2010, background): “However, Funck et al. (2008) showed localization of GFP-tagged OAT in the mitochondria, consistent with earlier reports of mitochondrial localization sequences in OAT (Delauney et al., 1993; Roosens et al., 1998).”
Drought, salt, and temperature stress-induced metabolic rearrangements and regulatory networks (2012, background): “…to enhance proline levels and to increase the stress tolerance of rice and tobacco (Roosens et al., 2002; Qu et al., 2005) even though Arabidopsis plants deficient in d-OAT accumulated proline in response to stress and showed a salt stress tolerance similar to the wild type (Funck et al., 2008).”
Non-protein amino acids: plant, soil and ecosystem interactions (2011, background): “Ornithine is converted by ornithine-δaminotransferase (δOAT) in mitochondria to pyrroline-5-carboxylate (P5C) (Funck et al. 2008).”