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Ornithine-delta-aminotransferase is essential for arginine catabolism but not for proline biosynthesis.

Funck D, Stadelhofer B, Koch W - BMC Plant Biol. (2008)

Bottom Line: Our findings indicate that deltaOAT 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Plant Physiology and Biochemistry, Biology Section, University of Konstanz, Universitätsstrasse 10, 78464 Konstanz, Germany. dietmar.funck@uni-konstanz.de

ABSTRACT

Background: Like 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).

Results: We show here that ornithine-delta-aminotransferase (deltaOAT, 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 deltaOAT, 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 deltaOAT expression.

Conclusion: Our findings indicate that deltaOAT 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.

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Related in: MedlinePlus

oat mutants display the same salt stress responses as wildtype plants. A: Col-0 wildtype, oat1 and oat3 were grown for three weeks in sterile culture on MS medium supplemented with 60 mM sucrose and increasing amounts of NaCl. B: Free Pro levels in 3-week-old plants. C: Fw/Dw ratios of plants cultivated under the same conditions. Columns represent the average of 3 (C) or at least 4 (B) independent biological replicates, error bars indicate SD.
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Figure 3: oat mutants display the same salt stress responses as wildtype plants. A: Col-0 wildtype, oat1 and oat3 were grown for three weeks in sterile culture on MS medium supplemented with 60 mM sucrose and increasing amounts of NaCl. B: Free Pro levels in 3-week-old plants. C: Fw/Dw ratios of plants cultivated under the same conditions. Columns represent the average of 3 (C) or at least 4 (B) independent biological replicates, error bars indicate SD.

Mentions: To investigate a potential function of δOAT in stress-induced Pro accumulation, we cultivated wildtype, oat1 and oat3 in sterile culture on media containing increasing amounts of NaCl (Fig. 3A). The mutants displayed similar sensitivity towards NaCl as the wildtype and seedling establishment was almost completely blocked in all three genotypes by the addition of more than 100 mM NaCl. Quantification of free Pro content in 3-week-old plants revealed no significant differences between wildtype and oat mutants, neither under control conditions nor after salt stress (Fig. 3B). In all three genotypes the content of free Pro was increased approximately 3-fold by the addition of 100 mM NaCl. Similar Fw/Dw ratios in wildtype and oat mutants under all salt concentrations further supported an equal stress tolerance in both genotypes (Fig. 3C). These findings indicate that δOAT does not contribute significantly to stress-induced Pro biosynthesis in vivo during salt stress. Additional evidence against a direct entry of Orn-derived P5C into Pro biosynthesis was derived from public microarray-expression data analysed with the BAR e-northern web-tool [28,29]. Over a large set of stress experiments, δOAT mRNA levels are in much closer correlation to P5CDH mRNA than to P5CR mRNA (data not shown).


Ornithine-delta-aminotransferase is essential for arginine catabolism but not for proline biosynthesis.

Funck D, Stadelhofer B, Koch W - BMC Plant Biol. (2008)

oat mutants display the same salt stress responses as wildtype plants. A: Col-0 wildtype, oat1 and oat3 were grown for three weeks in sterile culture on MS medium supplemented with 60 mM sucrose and increasing amounts of NaCl. B: Free Pro levels in 3-week-old plants. C: Fw/Dw ratios of plants cultivated under the same conditions. Columns represent the average of 3 (C) or at least 4 (B) independent biological replicates, error bars indicate SD.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2377265&req=5

Figure 3: oat mutants display the same salt stress responses as wildtype plants. A: Col-0 wildtype, oat1 and oat3 were grown for three weeks in sterile culture on MS medium supplemented with 60 mM sucrose and increasing amounts of NaCl. B: Free Pro levels in 3-week-old plants. C: Fw/Dw ratios of plants cultivated under the same conditions. Columns represent the average of 3 (C) or at least 4 (B) independent biological replicates, error bars indicate SD.
Mentions: To investigate a potential function of δOAT in stress-induced Pro accumulation, we cultivated wildtype, oat1 and oat3 in sterile culture on media containing increasing amounts of NaCl (Fig. 3A). The mutants displayed similar sensitivity towards NaCl as the wildtype and seedling establishment was almost completely blocked in all three genotypes by the addition of more than 100 mM NaCl. Quantification of free Pro content in 3-week-old plants revealed no significant differences between wildtype and oat mutants, neither under control conditions nor after salt stress (Fig. 3B). In all three genotypes the content of free Pro was increased approximately 3-fold by the addition of 100 mM NaCl. Similar Fw/Dw ratios in wildtype and oat mutants under all salt concentrations further supported an equal stress tolerance in both genotypes (Fig. 3C). These findings indicate that δOAT does not contribute significantly to stress-induced Pro biosynthesis in vivo during salt stress. Additional evidence against a direct entry of Orn-derived P5C into Pro biosynthesis was derived from public microarray-expression data analysed with the BAR e-northern web-tool [28,29]. Over a large set of stress experiments, δOAT mRNA levels are in much closer correlation to P5CDH mRNA than to P5CR mRNA (data not shown).

Bottom Line: Our findings indicate that deltaOAT 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Plant Physiology and Biochemistry, Biology Section, University of Konstanz, Universitätsstrasse 10, 78464 Konstanz, Germany. dietmar.funck@uni-konstanz.de

ABSTRACT

Background: Like 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).

Results: We show here that ornithine-delta-aminotransferase (deltaOAT, 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 deltaOAT, 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 deltaOAT expression.

Conclusion: Our findings indicate that deltaOAT 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.

Show MeSH
Related in: MedlinePlus