Over-expression of the transcription factor HlMYB3 in transgenic hop (Humulus lupulus L. cv. Tettnanger) modulates the expression of genes involved in the biosynthesis of flavonoids and phloroglucinols

Genes belonging to the R2R3 MYB transcription factor family play an important role in the regulation of the expression of structural genes involved in the biosynthesis of flavonoids. In this study, the regulatory gene s-HlMYB3 under the control of the CaMV 35S promoter was genetically transformed into hop cv. Tettnanger. This work was aimed at investigating the effect of s-HlMYB3 on the expression of genes involved in the biosynthesis of flavonoids and phloroglucinols. The transgene s-HlMYB3 was stably integrated and expressed in transgenic plants. Quantitative real-time PCR indicated that HlMYB3 was highly over-expressed in transgenic events compared to wildtype plants. The effect of the over-expressed transgene on the expression rate of structural genes of flavonoid and phloroglucinol biosynthesis, such as PAL, C4H, 4CL, CHS_H1, CHI, F3H, F3'H, FLS, F3'5'H, OMT1, HlPT1, and VPS, as well as on regulatory genes of hop like, HlMYB1, HlMYB2, HlMYB7, HlbZip1, HlbZip2, HlbHLH2, and WDR1 was examined. Transgenic events with an elevated expression of genes of flavonoids and phloroglucinols were identified. Chemical analysis revealed higher levels of cohumulone and colupulone in transgenic plants. In hop, flavonoids and phloroglucinols play an important role as flavoring compounds of beer. Moreover, prenylated chalcones (e.g. xanthohumol and desmethylxanthohumol) have received considerable attention because of their pharmacological properties. Metabolic engineering using genes of homologous MYB transcription factors may open the possibility for increasing the production of important secondary metabolites in hop.