Strigolactones in chemical ecology: waste products or vital allelochemicals?

Parasitic weeds of the genera Striga, Orobanche and Alectra are responsible for large-scale crop devastation in much of the world's most marginal agricultural land. Germination of the parasite seeds is critically dependent on the secretion of carotenoid-derived metabolites known as strigolactones from the roots of the host crops. Recent research into the origins and function of strigolactones has begun to elucidate the strigolactone biosynthetic pathway. The possibility that this pathway might be universally present in the angiosperms and that strigolactones may fulfil other crucial ecological roles has led to a renewed interest in the isolation and characterisation of these compounds. Biochemical and ecological studies on the mode of action of strigolactones also require support from the synthetic chemist. For this purpose several efficient stereocontrolled synthetic schemes have been devised, both for natural strigolactones and for a wide range of analogues. This review surveys the existing literature on the occurrence, isolation, biosynthetic origins and mode of action of strigolactones, and the methods for their synthesis. Knowledge of their origin and properties is expected to contribute significantly towards the science of crop protection in the 21st century, giving this largely overlooked class of metabolites a pivotal position in the effort towards poverty relief in the developing world.