Molecular Evolution of Pyrrolizidine Alkaloid Biosynthesis in the Tribe Crotalarieae (Fabaceae)

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Pyrrolizidine alkaloids (PAs) are a group of toxins that are produced as part of the plants chemical defense against herbivores. They occur in various unrelated families of the Angiosperms. Studies on the first specific enzyme of PA biosynthesis, homospermidine synthase (HSS), suggest that PA biosynthesis evolved several times independently during angiosperm evolution. One of these lineages is the legume family (Fabaceae), the third largest family of flowering plants, in which only two genera are described to contain PA-producing species: Crotalaria and Lotononis. Recently, we have been able to show that PA biosynthesis is, at least in Crotalaria, dependent on symbiosis with Rhizobia. Therefore, Crotalaria and related species are a unique system to study the physiology and evolution of this link between nodulation and alkaloid biosynthesis. In this project we will study the localization and regulation of PA biosynthesis and will compare this data with that of related plants producing quinolizidine alkaloids (QAs). Analyses of alkaloid profiles and sequences encoding HSS and its paralogue deoxyhypusine synthase will shed light in the evolution of PA biosynthesis in the Crotalarieae, a trait that most likely has its origin in QA-producing ancestors.