Trends in Plant Science
ReviewBiosynthesis of glucosinolates – gene discovery and beyond
Section snippets
Expanding the glucosinolate gene inventory
Glucosinolates are secondary metabolites well-known for their role in plant resistance to insects and pathogens and for their cancer-preventive properties. They are largely found in the order Brassicales which includes the economically and nutritionally important Brassica crops, such as oilseed rape (Brassica napus), cabbage (Brassica oleracea) and the model plant Arabidopsis (Arabidopsis thaliana) [1].
Glucosinolates have obtained status as ‘model’ secondary metabolites, and scientists in the
Biosynthesis overview
Glucosinolates are derived from amino acids and can thus be divided into three groups according to their amino acid precursor: aliphatic glucosinolates, derived from Ala, Leu, Ile, Val, and Met; benzenic glucosinolates, derived from Phe or Tyr; and indolic glucosinolates, derived from Trp. Biosynthesis proceeds through three independent stages: (i) chain elongation of selected precursor amino acids (only Met and Phe), (ii) formation of the core glucosinolate structure, and (iii) secondary
Side-chain elongation of Met – the resemblance to Leu biosynthesis
Before entering the core structure pathway, Met undergoes chain elongation (Figure 1a) in a process similar to the conversion of the branched-chain amino acid Val to its chain-elongated homolog Leu. The process starts with a deamination by a branched-chain amino acid aminotransferase (BCAT), which gives rise to a 2-oxo acid (Figure 1, step 1 to 2). The 2-oxo acid then enters a cycle of three successive transformations: condensation with acetyl-CoA by a methylthioalkylmalate synthase (MAM) (
Compartmentalization – the need for transport of intermediates
BCAT4 catalyzes the first reaction in the chain elongation process, and is localized in the cytosol [19], whereas the remaining enzymes involved in chain elongation are localized in the chloroplast 6, 10, 20, 30, 33, 34. This indicates the need for import of 2-oxo acids into the chloroplast and for export of chain-elongated amino acids into the cytosol, where biosynthesis of the core glucosinolate structure is believed to take place [1]. The chloroplast-localized bile acid transporter BAT5 was
Constructing the glucosinolate core – the importance of sulfur incorporation
The formation of the glucosinolate core structure seemed almost completely elucidated by 2006, where 13 enzymes representing five different biochemical steps had already been characterized 1, 35. Briefly, precursor amino acids are converted to aldoximes by cytochromes P450 of the CYP79 family (Figure 1, step 6 to 7). CYP79B2 and CYP79B3 both metabolize Trp 36, 37, CYP79A2 uses Phe as a substrate [38], CYP79F1 converts all chain-elongated Met derivatives, and CYP79F2 only converts the
Secondary modifications – the decoration that creates structural biodiversity
The biological activity of glucosinolates is to a large extent determined by the structure of the side chain [21], which makes secondary modifications particularly interesting from an application perspective. For aliphatic glucosinolates, secondary modifications include oxygenations, hydroxylations, alkenylations and benzoylations (Figure 1c). Indolic glucosinolates, in turn, can undergo hydroxylations and methoxylations (Figure 1c).
What is beyond gene discovery?
With the near-complete inventory of glucosinolate biosynthetic genes, one of the next goals in glucosinolate research is to understand the channeling of intermediates to the final product, which may be enabled by the presence of a biosynthetic multi-enzyme complex, also termed ‘metabolon’ [64]. Furthermore, virtually nothing is known about the transport of glucosinolates from their production site to the proper storage site. Regulation of flux through the pathway might be affected by
Acknowledgements
This work was supported by the Villum Kann Rasmussen (VKR) Foundation grant to VKR Research Centre for Pro-Active Plants.
References (72)
Elucidation of gene-to-gene and metabolite-to-gene networks in Arabidopsis by integration of metabolomics and transcriptomics
J. Biol. Chem.
(2005)Forward genetics and map-based cloning approaches
Trends Plant Sci.
(2003)- et al.
Genomics tools for QTL analysis and gene discovery
Curr. Opin. Plant Biol.
(2004) The chemical diversity and distribution of glucosinolates and isothiocyanates among plants
Phytochemistry
(2001)Glucosinolate biosynthesis: demonstration and characterization of the condensing enzyme of the chain elongation cycle in Eruca sativa
Phytochemistry
(2004)- et al.
Glucosinolate metabolism and its control
Trends Plant Sci.
(2006) Cytochrome P450 CYP79B2 from Arabidopsis catalyzes the conversion of tryptophan to indole-3-acetaldoxime, a precursor of indole glucosinolates and indole-3-acetic acid
J. Biol. Chem.
(2000)- et al.
Cytochrome P450 CYP79A2 from Arabidopsis thaliana L. catalyzes the conversion of L-phenylalanine to phenylacetaldoxime in the biosynthesis of benzylglucosinolate
J. Biol. Chem.
(2000) Cytochrome p450 CYP79F1 from Arabidopsis catalyzes the conversion of dihomomethionine and trihomomethionine to the corresponding aldoximes in the biosynthesis of aliphatic glucosinolates
J. Biol. Chem.
(2001)CYP83b1 is the oxime-metabolizing enzyme in the glucosinolate pathway in Arabidopsis
J. Biol. Chem.
(2001)
Desulfoglucosinolate sulfotransferases from Arabidopsis thaliana catalyze the final step in the biosynthesis of the glucosinolate core structure
J. Biol. Chem.
The biosynthesis of benzoic acid glucosinolate esters in Arabidopsis thaliana
Phytochemistry
Variation of glucosinolate accumulation among different organs and developmental stages of Arabidopsis thaliana
Phytochemistry
Purification and specificity of the C-S lyase of Albizzia lophanta
Biochem. Biophys. Acta
Roles for glutathione transferases in plant secondary metabolism
Phytochemistry
Biology and biochemistry of glucosinolates
Annu. Rev. Plant Biol.
Transcriptional co-regulation of secondary metabolism enzymes in Arabidopsis: functional and evolutionary implications
Plant Mol. Biol.
Omics-based identification of Arabidopsis Myb transcription factors regulating aliphatic glucosinolate biosynthesis
Proc. Natl. Acad. Sci. U. S. A.
A systems biology approach identifies a R2R3 MYB gene subfamily with distinct and overlapping functions in regulation of aliphatic glucosinolates
PLoS ONE.
Omics-based approaches to methionine side-chain elongation in Arabidopsis: characterization of the genes encoding methylthioalkylmalate isomerase and methylthioalkylmalate dehydrogenase
Plant Cell Physiol.
Arabidopsis bile acid: sodium symporter family protein 5 is involved in methionine-derived glucosinolate biosynthesis
Plant Cell Physiol.
Glucosinolate engineering identifies a gamma-glutamyl peptidase
Nat. Chem. Biol.
Arabidopsis branched-chain aminotransferase 3 functions in both amino acid and glucosinolate biosynthesis
Plant Physiol.
A redox-active isopropylmalate dehydrogenase functions in the biosynthesis of glucosinolates and leucine in Arabidopsis
Plant J.
Glucosinolate metabolites required for an Arabidopsis innate immune response
Science
Identification of a flavin monoxygenase as the S-oxygenating enzyme in aliphatic glucosinolate biosynthesis in Arabidopsis
Plant J.
A gene controlling variation in Arabidopsis glucosinolate composition is part of the methionine chain elongation pathway
Plant Physiol.
The gene controlling the indole glucosinolate modifier1 quantitative trait locus alters indole glucosinolate structures and aphid resistance in Arabidopsis
Plant Cell
Gene duplication in the diversification of secondary metabolism: tandem 2-oxoglutarate-dependent dioxygenases control glucosinolate biosynthesis in Arabidopsis
Plant Cell
A novel 2-oxoacid-dependent dioxygenase involved in the formation of the goiterogenic 2-hydroxybut-3-enyl glucosinolate and generalist insect resistance in Arabidopsis
Plant Physiol.
BRANCHED-CHAIN AMINOTRANSFERASE4 is part of the chain elongation pathway in the biosynthesis of methionine-derived glucosinolates in Arabidopsis
Plant Cell
Arabidopsis thaliana encodes a bacterial-type heterodimeric isopropylmalate isomerase involved in both Leu biosynthesis and the Met chain elongation pathway of glucosinolate formation
Plant Mol. Biol.
Role of glucosinolates in insect-plant relationships and multitrophic interactions
Annu. Rev. Entomol.
Molecular basis for chemoprevention by sulforaphane: a comprehensive review
Cell Mol. Life Sci.
Glucosinolates, isothiocyanates and human health
Phytochem. Rev.
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