title: Combinatorial analysis of lupulin gland transcription factors from R2R3Myb, bHLH and WDR families indicates a complex regulation of chs_H1 genes essential for prenylflavonoid biosynthesis in hop (Humulus Lupulus L.).
abstract: BACKGROUND
  Lupulin glands of hop produce a specific metabolome including hop bitter acids valuable for the brewing process and prenylflavonoids with promising health-beneficial activities. The detailed analysis of the transcription factor (TF)-mediated regulation of the oligofamily of one of the key enzymes, i.e., chalcone synthase CHS_H1 that efficiently catalyzes the production of naringenin chalcone, a direct precursor of prenylflavonoids in hop, constitutes an important part of the dissection of the biosynthetic pathways leading to the accumulation of these compounds.
  
  
  RESULTS
  Homologues of flavonoid-regulating TFs HlMyb2 (M2), HlbHLH2 (B2) and HlWDR1 (W1) from hop were cloned using a lupulin gland-specific cDNA library from the hop variety Osvald's 72. Using a "combinatorial" transient GUS expression system it was shown that these unique lupulin-gland-associated TFs significantly activated the promoter (P) of chs_H1 in ternary combinations of B2, W1 and either M2 or the previously characterized HlMyb3 (M3). The promoter activation was strongly dependent on the Myb-P binding box TCCTACC having a core sequence CCWACC positioned on its 5' end region and it seems that the complexity of the promoter plays an important role. M2B2W1-mediated activation significantly exceeded the strength of expression of native chs_H1 gene driven by the 35S promoter of CaMV, while M3B2W1 resulted in 30% of the 35S:chs_H1 expression level, as quantified by real-time PCR. Another newly cloned hop TF, HlMyb7, containing a transcriptional repressor-like motif pdLNLD/ELxiG/S (PDLNLELRIS), was identified as an efficient inhibitor of chs_H1-activating TFs. Comparative analyses of hop and A. thaliana TFs revealed a complex activation of Pchs_H1 and Pchs4 in combinatorial or independent manners.
  
  
  CONCLUSIONS
  This study on the sequences and functions of various lupulin gland-specific transcription factors provides insight into the complex character of the regulation of the chs_H1 gene that depends on variable activation by combinations of R2R3Myb, bHLH and WDR TF homologues and inhibition by a Myb repressor.
authors.affiliation: Biology Centre ASCR vvi, Institute of Plant Molecular Biology, Branišovská 31, 370 05 České Budějovice, Czech Republic. jmat@umbr.cas.cz
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Matoušek
authors.forename: Tomáš
authors.initials: T
authors.lastname: Kocábek
authors.forename: Josef
authors.initials: J
authors.lastname: Patzak
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Füssy
authors.forename: Jitka
authors.initials: J
authors.lastname: Procházková
authors.forename: Arne
authors.initials: A
authors.lastname: Heyerick
mesh_terms: D005419:Flavonoids / Q000096:biosynthesis*; D027582:Humulus / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D005419:Flavonoids; D010940:Plant Proteins; D014157:Transcription Factors