Strigolactones and their role in arbuscular mycorrhizal symbiosis

Abstract

Molecular signals are exchanged between arbuscular mycorrhizal (AM) fungi and their host plants during the pre-symbiotic stage, and help mutual recognition prior to any contact between the two partners. In particular, root exudates from host plants are known to trigger a switch in fungal development and metabolism, committing the fungus towards the establishment of the symbiosis. Strigolactones, a group of carotenoid-derived metabolites exuded by plant roots, are major contributors to this effect. Their importance in the normal development of mycorrhizae has been established through the analysis of strigolactone-deficient mutants. Interestingly, strigolactones were previously known as germination stimulants of the parasitic plants Striga and Orobanche. In addition, our group and others recently proposed that strigolactones or related compounds are novel hormones regulating shoot branching in monocots and dicots. The activity of strigolactones on three different types of organisms has stimulated progress in the understanding of their functions. This chapter reviews the current knowledge of strigolactone structural features, and recent advances and prospects in the elucidation of their biosynthetic pathway and of their mode of action.