Résumé
Cafestol and kahweol are the two main diterpenes present in coffee beans. Various effects of these compounds have been shown or hypothesized on human health (cholesterol raising, anticarcinogenic compounds...). Despite their importance, little information is available on the genetic and molecular bases of their metabolism. The objectives of this study were multiple: i) evaluate inter and intraspecific diversity for a few species of the Coffea genus for cafestol, kawheol and 16OMC, ii) analyse the patterns of accumulation/degradation of cafestol and kahweol during coffee fruit development, iii) study the expression of the three genes controlling the initial steps of diterpenes biosynthesis (CPS, KO, KS) during coffee fruit development. Phenotypic analyses of coffee beans from different species (with several genotypes per species) allowed the observation of significant variability for cafestol, kahweol and 16OMC. In addition, intraspecific analysis (with several clones or open pollinated progenies by genotypes) also revealed significant level of variability stressing the potential to modify diterpenes contents using conventional breeding for the species analyzed. Evaluation of cafestol and kawheol concentrations in the different fruit tissues (pericarp, perisperm and endosperm) during fruit maturation revealed diverging patterns of accumulation/degradation depending on the diterpene/tissue considered. For both diterpenes, pericarp concentration was extremely low. In perisperm, accumulation of cafestol until 123 Days After Flowering (DAF) was then followed by a slight diminution until the last developmental stage possible to analyse (178 DAF). Concerning kahweol, perisperm concentration reached a maximum between 90-120 DAF and then presented a steep decline until the 178 DAF. In endosperm, progressive accumulations of both diterpenes were observed from 90 DAF to 212 DAF with slight decreases in the two last weeks of development (226 DAF). In-silico analysis of Coffea EST allowed the identification of partial Coffea cDNA corresponding to CPS, KO, KS. Analysis of these genes during fruit development was performed by quantitative PCR in separated tissues. Expression results were normalized according to the expression patterns obtained with 5 housekeeping genes. Expression results will be discussed regarding their interest towards the identification of the genes potentially involved in cafestol / kahweol concentration regulation. (Texte intégral)