Molecular background and networking putatively involved in regulation of lupulin gland metabolome-Results and prospects

Ongoing research on the field of molecular genetics of hop is based on intensive work of various models like A. thaliana and non-model plants, where some progress has been reached especially within last fifteen years in the field of gene regulation: e.g. functional architecture of chromatin, new classes of transcription factors (TFs) and the regulatory role of small RNAs in gene silencing. In particular, TFs interconnections organized in network and the functions of micro RNAs in regulation of TFs sketch in the complicated back loops during standard development or within pathogenesis and stressful conditions. Genetic background co-determining levels and composition of hop metabolome in the lupulin glands, and in particular Xanthohumol (X) production includes this complex regulation. According to our recent knowledge about the biosynthetic pathway leading to X and desmethylxanthohumol (DMX) in lupulin glands, last steps of the pathway are controlled by the chalcone synthase CHS_H1, prenyltransferase and O-methyltransferase 1. Despite relative simplicity of this pathway, quantitative character of inheritance of X and also bitter acids suggests a complexity of regulatory factors controlling the biosynthesis of these metabolites of lupulin. These genetic data are in accordance with our recent results on the involvement of several key transcription factors from Myb (M), bHLH (B) and WDR (W) families in the regulation of chs_H1 and omt1 gene by WRKY, W1 and silencing suppressors (unpublished). We have identified lupulin specific ternary MBW complexes (Hls-M3B2W1; M2B2W1) strongly activating chs_H1. In addition, the results show that some TFs act in binary (Hls-M3B2; M2B2; B2W; M1W1; WRKY1W1) interactions and that such complexes are quite selective for different promoters of chs-related genes. Moreover, we demonstrated the ability of some of TFs either to moderate (HlbZip1 and 2) or to inhibit (HlM7) transcription from chs_H1 and omt1 genes in heterologous systems. Therefore, new challenging task is to analyze regulatory network and regulatory functions of lupulin-specific TFs using transient and ectopic expression systems.

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We acknowledge the use of research infrastructure that has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 316304.