Repeated evolution of the pyrrolizidine alkaloid-mediated defense system in separate angiosperm lineages.
Species of several unrelated families within the angiosperms are able to constitutively produce pyrrolizidine alkaloids as a defense against herbivores. In pyrrolizidine alkaloid (PA) biosynthesis, homospermidine synthase (HSS) catalyzes the first specific step. HSS was recruited during angiosperm evolution from deoxyhypusine synthase (DHS), an enzyme involved in the posttranslational activation of eukaryotic initiation factor 5A. Phylogenetic analysis of 23 cDNA sequences coding for HSS and DHS of various angiosperm species revealed at least four independent recruitments of HSS from DHS: one within the Boraginaceae, one within the monocots, and two within the Asteraceae family. Furthermore, sequence analyses indicated elevated substitution rates within HSS-coding sequences after each gene duplication, with an increased level of nonsynonymous mutations. However, the contradiction between the polyphyletic origin of the first enzyme in PA biosynthesis and the structural identity of the final biosynthetic PA products needs clarification.
Institut für Pharmazeutische Biologie der Technischen Universität, 38106 Braunschweig, Germany.
Andreas
A
Reimann
Niknik
N
Nurhayati
Anita
A
Backenköhler
Dietrich
D
Ober
D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D017931:DNA Primers; D018076:DNA, Complementary; D019143:Evolution, Molecular; D019684:Magnoliopsida / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D011763:Pyrrolizidine Alkaloids / Q000378:metabolism*
D017931:DNA Primers; D018076:DNA, Complementary; D011763:Pyrrolizidine Alkaloids; D000587:Oxidoreductases Acting on CH-NH Group Donors; C063507:deoxyhypusine synthase; D019883:Alkyl and Aryl Transferases; C028376:homospermidine synthetase