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The development of unisexual flowers in maize and other plants proceeds through selective elimination of floral organs in an initially bisexual floral meristem. The essential character of the tasselseed 2 gene (TS2) in this cell-death pathway has been established previously. Molecular cloning of TS2 reveals membership to the evolutionarily conserved superfamily of short-chain dehydrogenases/reductases, but its substrate specificity remained unknown. Recombinant TS2 protein was produced in Escherichia coli, and purified to apparent homogeneity. Analytical ultracentrifugation and gel filtration experiments show that TS2 is a tetrameric enzyme. Thermal denaturation followed by circular dichroism spectroscopy reveals that TS2 binds NAD(H) and NAD(P)(H). Substrate screening demonstrates that TS2 converts steroids with specificities found at positions 3 and 17, and several dicarbonyl and quinone compounds, thus establishing TS2 as a plant 3beta/17beta-hydroxysteroid dehydrogenase and carbonyl/quinone reductase. Taken together, the genetic data and the substrate specificities determined suggest that TS2 converts specific plant compounds and acts as a prereceptor control mechanism, in a manner similar to that of mammalian hydroxysteroid dehydrogenases.

Original publication

DOI

10.1111/j.1742-4658.2007.05642.x

Type

Journal

FEBS J

Publication Date

03/2007

Volume

274

Pages

1172 - 1182

Keywords

Amino Acid Sequence, Cloning, Molecular, Escherichia coli, Hydrogen-Ion Concentration, Hydroxysteroid Dehydrogenases, Kinetics, Ligands, Molecular Sequence Data, NAD, NADP, Plant Proteins, Plants, Protein Denaturation, Protein Structure, Quaternary, Recombinant Proteins, Sequence Analysis, Protein, Sequence Homology, Amino Acid, Substrate Specificity, Temperature