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‘Molecular evolution of a plant defence system and its interactions exemplified with the PAs’

This project focuses on the evolutionary origin of PA-biosynthesis. Plants that are able to produce PAs occur scattered in some unrelated families of the angiosperms. Where do the enzymes involved in PA-biosynthesis come from? How they were recruited? How these enzymes were successfully integrated into a complete pathway? Where the regulatory elements came from?

 

Molecular origin of homospermidine synthase (HSS), key-enzyme in PA-biosynthesis

Our recent studies showed that the gene for HSS, the entry enzyme in PA-biosynthesis was recruited by gene duplication of the gene coding for deoxyhypusine synthase (DHS). DHS is an enzyme of primary metabolism ubiquitous within eukaryotes and archaea. It is involved in the posttranslational activation of a regulatory protein, the eukaryotic initiation factor 5A (eIF5A). We intend to get a more detailed knowledge about the evolutionary mechanisms involved in the gene recruition process by analyzing:

 

  • kinetic properties of the enzymes
  • gene expression patterns
  • tissue specific localization
  • promotor analysis
  • site-specific mutagenesis
  • genome structure

 

Publications

Ober D, Hartmann T (1999) Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. Proc Natl Acad Sci USA 96, 14777-14782

Ober D, Hartmann T (1999) Deoxyhypusine synthase from tobacco: cDNA isolation, characterization, and bacterial expression of an enzyme with extended substrate specificity. J Biol Chem 274, 32040-32047

Ober D, Harms R, Hartmann T (2000) Cloning and expression of homospermidine synthase from Senecio vulgaris: a revision. Phytochemistry 55, 305-309

Ober D, Hartmann T (2000) Phylogenetic origin of a secondary pathway: the case of pyrrolizidine alkaloids. Plant Mol Biol 44, 445-450

Moll S, Anke S, Kahmann U, Hänsch R, Hartmann T, Ober D (2002) Cell specific expression of homospermidine synthase, the entry enzyme of the pyrrolizidine alkaloids in Senecio vernalis in comparison to its ancestor deoxyhypusine synthase. Plant Physiol 130, 47-57

Ober D, Harms R, Witte L, Hartmann T (2003) Molecular evolution by change of function: alkaloid-specific homospermidine synthase is a deoxyhypusine synthase which lost its ability to bind the eIF5A precursor protein. J Biol Chem 278, 12805-12812

 

Is the PA-biosynthesis of mono- or polyphyletic origin?

In this part of the project we try to find an explanation for the isolated occurrence of PAs within the angiosperms. Was the ability to produce PAs established very early in angiosperm evolution and was followed by independent losses in several lineages or is the isolated occurrence of this pathway the result of convergent evolution, that means it was recruited several times independently? In the latter case we have to postulate not only the establishment of a single enzyme but of the whole pathway leading to essentially identical PA structures. As a first step we intend to answer this question for homospermidine synthase. Of this enzyme cDNA sequences of PA-producing species of different angiosperm families will be identified and compared to the respective cDNA sequences of DHS.

 

Publication

Ober D, Hartmann T (2000) Phylogenetic origin of a secondary pathway: the case of pyrrolizidine alkaloids. Plant Mol Biol 44, 445-450

 

Identification of further enzymes involved in PA biosynthesis

To improve our understanding of the evolutionary origin of PA biosynthesis, further enzymes involved in the pathway will be identified and characterized. The focus will be on the evolutionary origin as well as on the regulatory integration into a metabolic pathway.


 
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