Comparative evolutionary analysis of methylthioalkylmalate synthase genes and enzymes in the Capparales
JÜRGEN KROYMANN
Université Paris-Sud
Laboratoire d'Ecologie Systématique et Evolution
CNRS UMR 8079
Bâtiment 360
91405 Orsay Cedex
Frankreich
D-07743 Jena
juergen.kroymann@u-psud.fr
http://www.u-psud.fr/
Glucosinolates (mustard oil glycosides) are a diverse group of plant secondary compounds found in the order Capparales. Glucosinolates contribute to plant resistance against herbivorous insects and other pests, but they also influence the quality of agriculturally important crops.
The biosynthesis of aliphatic glucosinolates occurs in three independent stages, (i) carbon chain elongation of the precursor amino acid methionine, (ii) formation of the glucosinolate core structure, and (iii) carbon chain modification. Methylthioalkylmalate synthase (MAM) enzymes encoded at the MAM locus are responsible for the committed step in glucosinolate chain elongation, the condensation of a 2-oxo acid derived from methionine homologues with acetyl-CoA. The carbon chain lengths of aliphatic glucosinolates are highly variable in two families of the Capparales, the Brassicaceae and the Capparaceae.
We investigate the genetic and biochemical basis of variation in glucosinolate chain elongation in the Capparales. Experiments involve sequencing of bacterial artificial chromosomes harboring the MAM locus from a variety of crucifers, and biochemical characterization of MAM proteins encoded at this locus.
Our results show that the MAM locus evolves dynamically. MAM gene duplication events, biochemical neofunctionalization, and positive selection account for functional diversification in plant secondary metabolism1, while gene deletion, gene conversion, and balancing selection help maintaining metabolic diversity within species2,3.
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