Screening for genes involved in the biosynthesis of prenylated chalcones in hops (Humulus lupulus L.)

Important secondary metabolites, present in hops (Humulus lupulus L.), include a-acids and beta-acids, which are essential for the brewing of beer, as well as the prenylated chalcones, xanthohumol, and desmethylxanthohumol, which exhibit interesting bioactive properties. Their formation and accumulation in the three selected hop varieties, `Admiral', `Wye Challenger', and `Whitbread Golding Variety', were quantitatively monitored by high-performance liquid chromatography using UV detection. All target compounds were present from the onset of flowering, not only in female cones, but also in leaves of fully grown hops as well. During development from inflorescences to cones, levels gradually increased. Each hop variety exhibited individual accumulation rates and proper choice of a particular hop variety may be quite important as to the presence of bioactive hop-derived compounds in beer. From this viewpoint, the three hop varieties studied were screened for genes that determine the biosynthesis of prenylated chalcones. The approach involved cDNA-AFLP screening of female inflorescences of three varieties at different developmental stages. Full cDNA-AFLP analysis (256 primer combinations) should give insight into differential gene expression of genes involved in the biosynthesis of important secondary metabolites. Full gene sequences can then be isolated from genomic DNA and cDNA libraries. In the near future, cDNA-AFLP fragments displaying differential expression will also be screened for the presence of sequences homologous with respect to known O-Me-transferases, prenyltransferases, chalcone synthases and MYB regulatory factors. Selected cDNA-AFLP fragments will be sequenced and cloned thereby providing an entry into detailed examination of protein products.