Planta Med 2010; 76 - P025
DOI: 10.1055/s-0030-1264323

Evolution and function of progesterone 5β-reductase genes in angiosperms

J Munkert 1, P Bauer 1, M Brydziun 1, F Müller-Uri 1, W Kreis 1
  • 1Pharmazeutische Biologie, Biologie, Staudtstraße 5, 91058 Erlangen, Germany

About 60 genera of the angiosperms have been described to contain 5β-cardenolides [1, 2, 3]. They occur in monocots, basal eudicots, rosids and asterids. The unpredictable occurrence of 5β-cardenolides in the angiosperms raises the question whether this trait has evolved only once or several times during evolution. The analysis of genes suggested to be involved in cardenolide biosynthesis may help to address this question. Progesterone 5β-reductases (P5βR, P5βR2) are thought to catalyse a step in the 5β-cardenolide biosynthesis, namely the conversion of progesterone to 5β-pregnane-3,20-dione. Therefore we isolated 11 new P5βRs orthologues from several 5β-cardenolide-free and 5β-cardenolide-producing plant species. All sequences were analysed in silico and were shown to be highly conserved. They contain certain motifs that qualify them as members of a class of stereo-selective enone reductases. Phylogenetic analysis shows that in the angiosperms P5βRs form two separate clusters. The cladogramme generated from protein sequences showed that one cluster (Cluster II) of P5βRs correlated nicely with the assumed phylogenetic relationship of the species in the cluster. This implied that these genes have evolved from a common ancestral gene. A second cluster contained p5βr-genes of Populus, Vitis and D. purpurea. All three genera also contained paralogues in cluster II. In this group only the D. purpurea P5βR2 was recently described to encode a functional P5βR that can be induced by stress [4]. The occurrence of these closely related functional P5βRs in 5β-cardenolide-free and 5β-cardenolide-containig plants let us presume that cluster II P5βRs are involved in more than just 5β-cardenolide biosynthesis.

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3. Kreis, W., Müller-Uri, F. (2010), Biochemistry of sterols, cardiac glycosides, brassinosteroids, phytoecdysteroids and steroid saponins. In: Wink M. (Ed.) Biochemistry of Plant Secondary Metabolism. Volume 40, 2nd Ed. 304–363, CRC Press, Sheffield.

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