A Gene Controlling Variation in Arabidopsis Glucosinolate Composition Is Part of the Methionine Chain Elongation Pathway

Abstract

Arabidopsis and other Brassicaceae produce an enormous diversity of aliphatic glucosinolates, a group of methionine (Met)-derived plant secondary compounds containing a-thio-glucose moiety, a sulfonated oxime, and a variable side chain. We fine-scale mapped GSL-ELONG, a locus controlling variation in the side-chain length of aliphatic glucosinolates. Within this locus, a polymorphic gene was identified that determines whether Met is extended predominantly by either one or by two methylene groups to produce aliphatic glucosinolates with either three-or four-carbon side chains. Two allelic mutants deficient in four-carbon side-chain glucosinolates were shown to contain independent missense mutations within this gene. In cell-free enzyme assays, a heterologously expressed cDNA from this locus was capable of condensing 2-oxo-4-methylthiobutanoic acid with acetyl-coenzyme A, the initial reaction in Met chain elongation. The gene methylthioalkylmalate synthase1 (MAM1) is a member of a gene family sharing approximately 60% amino acid sequence similarity with 2-isopropylmalate synthase, an enzyme of leucine biosynthesis that condenses 2-oxo-3-methylbutanoate with acetyl-coenzyme A.

Genetic variation in leaf and stem glucosinolates in resynthesized lines of winter rapeseed (Brassica napus L.)

“…An assumption is that a difference in gene action causes this methionine side chain elongation. This makes it possible to further investigate gene controlled variation in leaves within Brassica napus L. (Kroymann et al 2000). In leaves of Brassica napus L., this is expressed in significant correlated levels of PRO and GNA (Gland et al 1981).…”

Evolution of plant resistance at the molecular level: ecological context of species interactions

“…Glucosinolates and their breakdown products are genetically variable in Arabidopsis and Brassica, and experience natural selection due to their biological effects on generalist and specialist herbivores (Mauricio and Rausher, 1997;Raybould and Moyes, 2001;Kliebenstein et al, 2002b). High levels of nucleotide polymorphism are maintained by balancing selection at the Arabidopsis GSelong locus (Kroymann and Mitchell-Olds, unpublished), which encodes a glucosinolate biosynthetic enzyme (Kroymann et al, 2001). Evolutionary forces influencing families of metabolites have also been investigated.…”

“…Current data reveal no tendency for the recognition or deployment phases of plant defense to evolve preferentially via trench warfare versus an evolutionary arms race (Stahl et al, 1999;Bergelson et al, 2001b;Kroymann et al, 2001;Stranger 2002;Zhang et al, 2002). Rather, balancing selection maintains ancient nucleotide polymorphisms at resistance loci encoding LRR recognition proteins and secondary metabolic enzymes (eg, Rpm1, Rps5, Rps2, GSelong).…”

A robust omics-based approach for the identification of glucosinolate biosynthetic genes

“…The reactions involved in Met side-chain elongation are similar to those involved in Leu biosynthesis; moreover, the enzymes involved in Met side-chain elongation and Leu biosynthesis are presumably encoded by homologous genes belonging to the same gene families. In fact, MAM genes and IPMS (isopropylmalate synthase) genes, which are responsible for Met side-chain elongation and Leu synthesis, respectively, share sequence similarity with each other and with bacterial IPMS (de Kraker et al 2007;Field et al 2004;Kroymann et al 2001). All of the above-mentioned candidate genes are under the transcriptional regulation involving Myb28 (Hirai et al 2007).…”

“…ATTED-II analysis using a whole dataset showed weak correlation between ESM1 and ESP (Epithiospecifier protein, At1g54040) (data not shown). MAM genes that encode one of the Met side-chain elongation enzymes were also identified and characterized on the basis of the QTL analysis (Field et al 2004;Textor et al 2004;Kroymann et al 2001Kroymann et al , 2003. To my knowledge, however, some other genes that are involved in Met side-chain elongation process, namely, MAM-I (coding for methylthioalkylmalate isomerase) and MAM-D (coding for methylthioalkylmalate dehydrogenase) have not been identified by QTL analysis, presumably because natural variation of these genes does not result in metabolic natural variation.…”