Gene Duplication in the Diversification of Secondary Metabolism: Tandem 2-Oxoglutarate–Dependent Dioxygenases Control Glucosinolate Biosynthesis in Arabidopsis

Abstract

Secondary metabolites are a diverse set of plant compounds believed to have numerous functions in plant-environment interactions. The large chemical diversity of secondary metabolites undoubtedly arises from an equally diverse set of enzymes responsible for their biosynthesis. However, little is known about the evolution of enzymes involved in secondary metabolism. We are studying the biosynthesis of glucosinolates, a large group of secondary metabolites, in Arabidopsis to investigate the evolution of enzymes involved in secondary metabolism. Arabidopsis contains natural variations in the presence of methylsulfinylalkyl, alkenyl, and hydroxyalkyl glucosinolates. In this article, we report the identification of genes encoding two 2-oxoglutarate-dependent dioxygenases that are responsible for this variation. These genes, AOP2 and AOP3 , which map to the same position on chromosome IV, result from an apparent gene duplication and control the conversion of methylsulfinylalkyl glucosinolate to either the alkenyl or the hydroxyalkyl form. By heterologous expression in Escherichia and the correlation of gene expression patterns to the glucosinolate phenotype, we show that AOP2 catalyzes the conversion of methylsulfinylalkyl glucosinolates to alkenyl glucosinolates. Conversely, AOP3 directs the formation of hydroxyalkyl glucosinolates from methylsulfinylalkyl glucosinolates. No ecotype coexpressed both genes. Furthermore, the absence of functional AOP2 and AOP3 leads to the accumulation of the precursor methylsulfinylalkyl glucosinolates. A third member of this gene family, AOP1 , is present in at least two forms and found in all ecotypes examined. However, its catalytic role is still uncertain.

Glucosinolates inBrassicavegetables: The influence of the food supply chain on intake, bioavailability and human health

“…Some of these modification genes have been characterised as 2-oxogluturate dependent dioxygenases [53,54] but other types of genes are also involved [55].…”

Plant SET domain-containing proteins: Structure, function and regulation

“…This is best exemplified by the diversification of genes involve in plant secondary metabolism through gene duplication [152,153]. Such gene duplication events offer a great opportunity for studying gene evolution [154,155].…”

Variations in CYP74B2 (Hydroperoxide Lyase) Gene Expression Differentially Affect Hexenal Signaling in the Columbia and Landsberg erecta Ecotypes of Arabidopsis

“…Together with the higher expression levels of CYP74B2 (HPL) transcripts and volatiles produced, these data suggest that the levels of JAs are also elevated in Ler leaves compared to Col leaves. Also interesting among the set more highly expressed in the Ler ecotype are several loci in aliphatic glucosinolate synthesis, including CYP79F1, which exists upstream of CYP83A1 (Hansen et al, 2001;Reintanz et al, 2001;Chen et al, 2003), CYP83A1 itself, and 2-oxoglutarate-dependent dioxygenase (AOP3), which exists downstream of CYP83A1 (Kliebenstein et al, 2001b); Trp synthetase (TSB2; Last et al, 1991) also potentially impacts aliphatic glucosinolate synthesis because it is postulated to feed substrates into the aliphatic glucosinolate pathway via CYP79B2 and CYP79B3 . Contrasting with these glucosinolate synthetic enzymes that are more highly expressed in the Ler ecotype, one locus more highly expressed in the Col ecotype codes for thioglycosyl hydrolase (TGG2, myrosinase), which degrades glucosinolates to release toxic derivatives (Xue et al, 1995).…”