Résumé
Species of the genus Coffea accumulate diterpenes of the ent-kaurane family in the endosperm of their seeds, of which cafestol and kahweol are the most abundant (ca. 1-2% DW). In contrast to the numerous studies on their effects on human health and therapeutic applications, nothing was previously known about their biological and ecological role in planta. The antifungal and anti-insect activity of cafestol was thus investigated in this study. Cafestol significantly affected the mycelial growth of five of the six phytopathogenic fungi tested. It also greatly reduced the percentage of pupation of larvae and the pupae and adult masses of one of the two fruit flies tested. Using confocal imaging and oil body isolation and analysis, we showed that diterpenes are localized in endosperm oil bodies. Diterpene measurements in all organs of seedlings recovered from whole seed germination or embryos isolated from the endosperm showed that diterpenes are transferred from the endosperm to the cotyledons during seedling growth and then distributed to all organs, including the hypocotyl and the root. Collectively, our findings show that coffee diterpenes are broad-spectrum defence compounds that protect not only the seed on the mother plant and in the soil, but also the seedling after germination. Furthermore, the genes and enzymes involved in the biosynthesis of cafestol and kahweol remain unknown. Phylogenetic analyses were first performed to identify and classify all terpene synthases and cytochromes P450 (CYPs) in the coffee genome. Then, using a large transcriptome dataset (14 species and 5 seed developmental stages per species) and genes coding for the enzymes that catalyze the synthesis of ent-kaurenoic acid as guide genes, seven candidate CYP genes were identified through gene coexpression network analysis. Their role in cafestol and kahweol biosynthesis is currently investigated using heterologous expression in yeast and tobacco in combination with GC- and LC-MS analysis.