Analysis of the chalcone synthase from Humulus lupulus L. and biotechnology aspects of medicinal hops

The complete sequence hop gene, which corresponds to true chalcone synthase (EC 2.3.1.74), was amplified using a combination of PCR, RT PCR and inverse PCR methods and cloned from Czech Osvald's clone 72. The gene designated chs_H1 was found to be specifically expressed on glandular trichomes, whereas negligible level of specific mRNA was found in leaves. Thus, chs_H1 may co-determine biosynthesis of prenylated chalcones, compounds valuable as anticancer and antiproliferative components of lupulin. It was shown by the comparative analyses and by the structure modelling that the true hop chalcone synthase differs from previously described CHS-like protein, phlorisovalerophenone synthase, which is involved in biosynthesis of bitter acids. Several hop cultivars were analysed for the presence of genes homologous to chs_H1 using chs_H1 cDNA as probe. 2-4 HindIII specific genomic fragments were detected by Southern blots, depending on cultivar. More detailed analysis revealed at least six homologous genes in Osvald's 72 hop, suggesting a great potential of this hop also as a genetic source for modern biotechnology. High level of xanthohumol in some Osvald's 72-derived hybrid cultivars like cv. Sládek, as well as a comparatively high level of prenylated flavonoids in some comprehensive hops, suggest also the presence of additional, regulatory genes co-determining levels of prenylated flavonoids valuable for medicinal hops.