Broad connections in the Arabidopsis seed metabolic network revealed by metabolite profiling of an amino acid catabolism mutant.

An Arabidopsis thaliana mutant was identified as having increases in 12 of 20 free proteogenic amino acids in seeds. Because these metabolites are produced from multiple, seemingly unrelated biosynthetic networks, it was not possible to use a candidate gene approach to discover the enzyme defect responsible for this complex syndrome. Complementary metabolite profiling analyses revealed increased seed homomethionine and isovaleroyloxypropyl-glucosinolate, along with reduced 3-benzoyloxypropyl-glucosinolate. These data led to the discovery of impaired branched chain amino acid catabolic enzyme isovaleryl-CoA dehydrogenase (encoded by gene At3g45300 or atIVD) as the cause of this metabolic syndrome. These results indicate that catabolism plays an important role in regulating levels of branched chain amino acids in seeds. The diverse set of metabolites affected in the ivd1 mutants suggests the existence of a more complex network regulating seed amino acid accumulation than previously observed. This combined targeted and non-targeted metabolite profiling approach is broadly applicable to the characterization of metabolic mutants, human disease studies and crop germplasm.