Genetic variations within the hop promoter genes for bitter acid and flavonoid biosynthesis partly explain phenotypic cultivar diversity

Pauline Seeburger is a BSc student at the University of Hohenheim in Stuttgart, Germany. Her research examines the role of regulatory elements of biosynthesis genes for the production of secondary metabolites in hop plants. The hop plant is rich in secondary metabolites of which the bitter acids are essential for the characteristic taste of beer. Bitter acids are produced in the glands of the female hop flower (cone) through the bitter acid biosynthesis pathway. The biosynthesis relies on three key enzymes: valerophenone synthase, prenyltransferase 1, and prenyltransferase 2. Prenyltransferase 1 has a double function and is a key element of the biosynthesis of the pharmacologically interesting hop flavonoids, xanthohumol and 8-prenylnaringenin. The study aims to examine the genes and gene regulation of these important enzymes. Transcription factors have a known regulatory function for genes when binding to promoter elements. Thus, variations in the promoter elements alter the gene expression, and might be associated with the bitter acid concentration in the hop cone. Promoter elements of the bitter acid biosynthesis genes and related pathways have been sequenced. Variations within these elements evoke different concentrations of bitter acids, especially the alpha acid, among hop varieties. The results showed that knowledge-based targeted sequencing is suitable for the identification of associations between variants in the genotype and phenotypic traits. Significant gene-trait associations were found in promoters of both prenyltransferase genes, and surprisingly, in a gene promotor from anthocyanin biosynthesis. In the long-term, the study of these promotors could be the basis for developing molecular markers to improve hop breeding strategies to reduce the time and cost to create new varieties with high alpha acid content.

Pauline Seeburger won the ISHS Prof. Jens Wünsche Young Minds Award for the best oral presentation at the V International Humulus Symposium, which was held virtually in Germany in March 2021.

Pauline Seeburger, Department of Crop Physiology of Specialty Crops, University of Hohenheim, Emil-Wolff-Straße 23, 70599 Stuttgart, Germany, e-mail: pauline.seeburger@uni-hohenheim.de

The article is available in Chronica Horticulturae