Two Arabidopsis threonine aldolases are nonredundant and compete with threonine deaminase for a common substrate pool

Plant Cell. 2006 Dec;18(12):3564-75. doi: 10.1105/tpc.106.044958. Epub 2006 Dec 15.

Abstract

Amino acids are not only fundamental protein constituents but also serve as precursors for many essential plant metabolites. Although amino acid biosynthetic pathways in plants have been identified, pathway regulation, catabolism, and downstream metabolite partitioning remain relatively uninvestigated. Conversion of Thr to Gly and acetaldehyde by Thr aldolase (EC 4.1.2.5) was only recently shown to play a role in plant amino acid metabolism. Whereas one Arabidopsis thaliana Thr aldolase (THA1) is expressed primarily in seeds and seedlings, the other (THA2) is expressed in vascular tissue throughout the plant. Metabolite profiling of tha1 mutants identified a >50-fold increase in the seed Thr content, a 50% decrease in seedling Gly content, and few other significant metabolic changes. By contrast, homozygous tha2 mutations cause a lethal albino phenotype. Rescue of tha2 mutants and tha1 tha2 double mutants by overproduction of feedback-insensitive Thr deaminase (OMR1) shows that Gly formation by THA1 and THA2 is not essential in Arabidopsis. Seed-specific expression of feedback-insensitive Thr deaminase in both tha1 and tha2 Thr aldolase mutants greatly increases seed Ile content, suggesting that these two Thr catabolic enzymes compete for a common substrate pool.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aldehyde-Lyases / genetics
  • Aldehyde-Lyases / metabolism*
  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Cloning, Molecular
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Plant
  • Genes, Essential
  • Genes, Recessive
  • Glucuronidase / metabolism
  • Glycine Hydroxymethyltransferase / genetics
  • Glycine Hydroxymethyltransferase / metabolism*
  • Isoleucine / metabolism
  • Mutation / genetics
  • Phenotype
  • Seedlings / enzymology
  • Seeds / enzymology
  • Substrate Specificity
  • Threonine / chemistry
  • Threonine / metabolism
  • Threonine Dehydratase / metabolism*
  • Yeasts / cytology

Substances

  • Arabidopsis Proteins
  • Isoleucine
  • Threonine
  • Glycine Hydroxymethyltransferase
  • Glucuronidase
  • Aldehyde-Lyases
  • THA1 protein, Arabidopsis
  • THA2 protein, Arabidopsis
  • Threonine Dehydratase