Journal Article

Combinatorial analysis of lupulin gland transcription factors from R2R3Myb, bHLH and WDR families indicates a complex regulation of chs _(H)1 genes essential for prenylflavonoid biosynthesis in hop

Matou?ek, Jaroslav, Patzak, Josef, Procházková, Jitka, Füssy, Zoltán, Heyerick, Arne, Kocábek, Tomá?

2012

Overview

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_(H)1 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. 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_(H)1 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_(H)1 gene driven by the 35S promoter of CaMV, while M3B2W1 resulted in 30% of the 35S:chs_(H)1 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_(H)1-activating TFs. Comparative analyses of hop and A. thaliana TFs revealed a complex activation of Pchs_(H)1 and Pchs4 in combinatorial or independent manners. 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_(H)1 gene that depends on variable activation by combinations of R2R3Myb, bHLH and WDR TF homologues and inhibition by a Myb repressor.

• Publisher: BioMed Central Ltd,BioMed Central,BMC
• Subject: Metabolites / Physiological aspects / Transcription factors