MBE Advance Access published online on July 24, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn161
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Research Article |
Evolutionary diversification in polyamine biosynthesis
* Instituto de Biología Molecular y Celular de Plantas (UPV – CSIC) Universidad Politécnica de Valencia 46022 Valencia (Spain)
Departamento de Genómica y Proteómica Instituto de Biomedicina de Valencia (CSIC) and CIBERER 46010 Valencia (Spain)
Corresponding author: Miguel A. Blázquez IBMCP (UPV-CSIC) Universidad Politécnica de Valencia Avda de los Naranjos s/n 46022 Valencia (Spain) Phone nr.: +34 963877886 Fax nr.: +34 963877859 e-mail: mblazquez{at}ibmcp.upv.es
Received for publication May 14, 2008. Revision received July 13, 2008. Accepted for publication July 15, 2008.
Polyamine biosynthesis is an ancient metabolic pathway present in all organisms. Aminopropyltransferases are key enzymes that mediate the synthesis of spermidine, spermine, and thermospermine. The relatively high sequence similarity between aminopropyltransferases, and their similarity with putrescine N-methyltransferases (PMT) raises the question of whether they share a common ancestor or have evolved by convergence. Here we show that aminopropyltransferases and PMT are phylogenetically interconnected and the different activities have been generated by unusually frequent events of diversification of existing functions. While all spermidine synthases derive from a common ancestor preceding the separation between prokaryotes and eukaryotes, they have been the origin of a variety of new activities. Among those, spermine synthases represent a novelty independently arisen at least three times, in Animals, Fungi and Plants. The most parsimonious mechanism would involve the duplication and change of function of preexisting spermidine synthase genes in each phylum. Although spermine is not essential for life, the repeated invention of spermine synthase and its conservation strongly argues for an evolutionary advantage derived from its presence. Moreover, the appearance of thermospermine synthase in several genera of Archaea and Bacteria was accompanied by a loss of spermidine synthase, suggesting that the new activity originated as a change of function of this enzyme. Surprisingly, thermospermine synthase was later acquired by Plants at an early stage of evolution by horizontal gene transfer, and has proven to be essential for vascular development in tracheophytes. Finally, the synthesis of nicotine and tropane alkaloids in Solanales was favored by the origination of a new activity, putrescine N-methyltransferase, as a duplication and change of function from spermidine synthase.
Key Words: aminopropyl transferases • polyamine • putrescine • spermidine • spermine • evolution
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