ABSTRACT
Amino acid and glucosinolate biosynthesis are two interdependent pathways; amino acid synthesis as a part of primary metabolism provides the precursors for glucosinolate biosynthesis in secondary metabolism. In our previous studies, the combination of coexpression analysis and metabolite profiling led to the identification of genes and key regulators involved in glucosinolate biosynthesis. Moreover, the integration of transcriptome and metabolome data of sulphur-deprived Arabidopsis plants revealed coordinate changes in the expression profiles of genes involved in glucosinolate and amino acid metabolism.This review provides an overview of our recent studies involving Arabidopsis mutant plants that exhibit impairment in the side-chain elongation process occurring during aliphatic glucosinolate biosynthesis by means of coexpression analysis and a novel metabolite profiling approach based on ultra-performance liquid chromatography coupled with tandem quadrupole mass spectrometry (UPLC-TQMS) (Sawada et al. 2009a). Thus, this review highlights the advantages of the omics-based approach in identifying genes involved in glucosinolate biosynthesis.
Subject(s)
Amino Acids/biosynthesis , Arabidopsis/genetics , Arabidopsis/metabolism , Glucosinolates/biosynthesis , Metabolomics , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Biosynthetic Pathways/genetics , Fatty Acids , Gene Expression Profiling , Gene Expression Regulation, Plant , Gene Knockout Techniques , Metabolic Networks and Pathways , Plants , Thioglucosides , Transcription FactorsABSTRACT
Glucosinolates (GSLs) are a group of plant secondary metabolites that have repellent activity against herbivore insects and pathogens, and anti-carcinogenic activity in humans. They are produced in plants of the Brassicaceae and other related families. Biosynthesis of GSLs from precursor amino acids takes place in two subcellular compartments; amino acid biosynthesis and side chain elongation occur mainly in the chloroplast, whereas the following core structure synthesis takes place in the cytosol. Although the genes encoding biosynthetic enzymes of GSLs are well known in Arabidopsis thaliana, the transporter genes responsible for translocation of biosynthetic intermediates between the chloroplast and cytosol are as yet unidentified. In this study, we identified the bile acid:sodium symporter family protein 5 (BASS5) gene in Arabidopsis as a candidate transporter gene involved in methionine-derived GSL (Met-GSL) biosynthesis by means of transcriptome co-expression analysis. Knocking out BASS5 resulted in a decrease of Met-GSLs and concomitant increase of methionine. A transient assay using fluorescence fusion proteins indicated a chloroplastic localization of BASS5. These results supported the idea that BASS5 plays a role in translocation across the chloroplast membranes of the biosynthetic intermediates of Met-GSLs.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/genetics , Glucosinolates/biosynthesis , Symporters/metabolism , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Chloroplasts/metabolism , DNA, Bacterial/genetics , Gene Expression Profiling , Gene Expression Regulation, Plant , Genes, Plant , Genotype , Metabolome , Mutagenesis, Insertional , RNA, Plant/genetics , Symporters/geneticsABSTRACT
Glucosinolates (GSLs) are secondary metabolites in Brassicaceae plants synthesized from amino acids. Methionine-derived GSLs (Met-GSLs) with diverse side chains of various lengths are the major GSLs in Arabidopsis. Methionine chain elongation enzymes are responsible for variations in chain length in Met-GSL biosynthesis. The genes encoding methionine chain elongation enzymes are considered to have been recruited from the leucine biosynthetic pathway in the course of evolution. Among them, the genes encoding methylthioalkylmalate synthases and aminotransferases have been identified; however, the remaining genes that encode methylthioalkylmalate isomerase (MAM-I) and methylthioalkylmalate dehydro-genase (MAM-D) remain to be identified. In a previous study based on transcriptome co-expression analysis, we identified candidate genes for the large subunit of MAM-I and MAM-D. In this study, we confirmed their predicted functions by targeted GSL analysis of the knockout mutants, and named the respective genes MAM-IL1/AtleuC1 and MAM-D1/AtIMD1. Metabolic profiling of the knockout mutants of methionine chain elongation enzymes, conducted by means of widely targeted metabolomics, implied that these enzymes have roles in controlling metabolism from methionine to primary and methionine-related secondary metabolites. As shown here, an omics-based approach is an efficient strategy for the functional elucidation of genes involved in metabolism.
