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Evolution of flux control in the glucosinolate pathway in Arabidopsis thaliana.

ABSTRACT: Network characteristics of biochemical pathways are believed to influence the rate of evolutionary change in constituent enzymes. One characteristic that may affect rate heterogeneity is control of the amount of product produced by a biochemical pathway or flux control. In particular, theoretical analyses suggest that adaptive substitutions should be concentrated in the enzyme(s) that exert the greatest control over flux. Although a handful of studies have found a correlation between position in a pathway and evolutionary rate, these investigations have not examined the relationship between evolutionary rate and flux control. Given that genes with greater control will experience stronger selection and that the probability of fixation is proportional to the selective advantage, we ask the following: 1) do upstream enzymes have majority flux control, 2) do enzymes with majority flux control accumulate adaptive substitutions, and 3) are upstream enzymes under higher selective constraint? First, by perturbing the enzymes in the aliphatic glucosinolate pathway in Arabidopsis thaliana with gene insertion lines, we show that flux control is focused in the first enzyme in the pathway. Next, by analyzing several sequence signatures of selection, we also show that this enzyme is the only one in the pathway that shows convincing evidence of selection. Our results support the hypothesis that natural selection preferentially acts on enzymes with high flux control.

SUBMITTER: Olson-Manning CF

PROVIDER: S-EPMC3525143 | biostudies-literature | 2013 Jan

REPOSITORIES: biostudies-literature

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Evolution of flux control in the glucosinolate pathway in Arabidopsis thaliana.

Olson-Manning Carrie F CF Lee Cheng-Ruei CR Rausher Mark D MD Mitchell-Olds Thomas T

Molecular biology and evolution 20120825 1

Network characteristics of biochemical pathways are believed to influence the rate of evolutionary change in constituent enzymes. One characteristic that may affect rate heterogeneity is control of the amount of product produced by a biochemical pathway or flux control. In particular, theoretical analyses suggest that adaptive substitutions should be concentrated in the enzyme(s) that exert the greatest control over flux. Although a handful of studies have found a correlation between position in ...[more]

PMID: 22923463

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Project description:Glucosinolates are plant secondary metabolites present in Brassicaceae plants such as the model plant Arabidopsis thaliana. Intact glucosinolates are believed to be biologically inactive, whereas degradation products after hydrolysis have multiple roles in growth regulation and defense. The degradation of glucosinolates is catalyzed by thioglucosidases called myrosinases and leads by default to the formation of isothiocyanates. The interaction of a protein called epithiospecifier protein (ESP) with myrosinase diverts the reaction toward the production of epithionitriles or nitriles depending on the glucosinolate structure. Here we report the identification of a new group of nitrile-specifier proteins (AtNSPs) in A. thaliana able to generate nitriles in conjunction with myrosinase and a more detailed characterization of one member (AtNSP2). Recombinant AtNSP2 expressed in Escherichia coli was used to test its impact on the outcome of glucosinolate hydrolysis using a gas chromatography-mass spectrometry approach. AtNSP proteins share 30-45% sequence homology with A. thaliana ESP. Although AtESP and AtNSP proteins can switch myrosinase-catalyzed degradation of 2-propenylglucosinolate from isothiocyanate to nitrile, only AtESP generates the corresponding epithionitrile. Using the aromatic benzylglucosinolate, recombinant AtNSP2 is also able to direct product formation to the nitrile. Analysis of glucosinolate hydrolysis profiles of transgenic A. thaliana plants overexpressing AtNSP2 confirms its nitrile-specifier activity in planta. In silico expression analysis reveals distinctive expression patterns of AtNSPs, which supports a biological role for these proteins. In conclusion, we show that AtNSPs belonging to a new family of A. thaliana proteins structurally related to AtESP divert product formation from myrosinase-catalyzed glucosinolate hydrolysis and, thereby, likely affect the biological consequences of glucosinolate degradation. We discuss similarities and properties of AtNSPs and related proteins and the biological implications.

Dataset Information

Evolution of flux control in the glucosinolate pathway in Arabidopsis thaliana.

Publications

Evolution of flux control in the glucosinolate pathway in Arabidopsis thaliana.

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