Arabidopsis thalianaG2‐LIKE FLAVONOID REGULATOR and BRASSINOSTEROID ENHANCED EXPRESSION1 are low‐temperature regulators of flavonoid accumulation

Abstract

Summary Flavonoid synthesis is predominantly regulated at the transcriptional level through the MYB−basic helix‐loop‐helix (bHLH)−WD40 (MBW) (MYB: transcription factor of the myeloblastosis protein family, WD40: tanscription factor with a short structural motif of 40 amino acids which terminates in an aspartic acid–tryptophan dipeptide) complex, and responds to both environmental and developmental stimuli. Although the developmental regulation of flavonoid accumulation in Arabidopsis thaliana has been examined in great detail, the response of the flavonoid synthesis pathway to abiotic stress (particularly low temperature) remains unclear. A screen of a Dissociation element (Ds) transposon‐induced mutation collection identified two lines which exhibited an altered profile of phenylpropanoid accumulation following exposure to low‐temperature stress. One of the mutated genes (BRASSINOSTEROID ENHANCED EXPRESSION1 (BEE1)) encoded a brassinosteroid enhanced expression transcription factor, while the other (G2‐LIKE FLAVONOID REGULATOR (GFR)) encoded a G2‐like flavonoid regulator. Phenylpropanoid‐targeted analysis was performed using high‐performance LC‐MS, and gene expression analysis using quantitative reverse transcription−PCR. In both mutants, the accumulation of quercetins and scopolin was reduced under low‐temperature growing conditions, whereas that of anthocyanin was increased. BEE1 and GFR were both shown to negatively regulate anthocyanin accumulation by inhibiting anthocyanin synthesis genes via the suppression of the bHLH (TRANSPARENT TESTA8 (TT8) and GLABROUS3 (GL3)) and/or the MYB (PRODUCTION OF ANTHOCYANIN PIGMENTS2 (PAP2)) components of the MBW complex. Our results provide new insight into the regulatory control of phenylpropanoid metabolism at low temperatures, and reveal that BEE1 and GFR act as important components of the signal transduction chain.

Accumulation of the coumarin scopolin under abiotic stress conditions is mediated by the Arabidopsis thaliana THO/TREX complex

“…The exposure of wild type plants to 10°C for 1 week induced an altered content in ~300 compounds in leaves; most prominent among these (apart from scopolin) were kaempferol and quercetin derivatives, sinapoyl glucose and a number of nitrogen‐ and sulphur‐containing compounds (Petridis et al ., ). A comparison between wild type and the two independent tho1 mutants identified only four compounds (in addition to scopolin) of 4000 extracted and aligned features that were altered in tho1 (Col‐0) and tho1 (Ws) in a similar fashion; all of these were sulphur‐containing compounds with low signal intensities.…”

“…LC‐MS was carried out as described previously (Petridis et al ., ). In short, samples were separated on an Acquity UPLC ® BEH Phenyl Column (130Å, 2.1 × 100 mm, 1.7 μm) with an Acquity UPLC ® BEH Phenyl VanGuard precolumn (130Å, 2.1 × 5 mm, 1.7 μm; Waters, Eschborn, Germany).…”

“…Antagonistic roles of the TFs MYB12 and MYB4 in scopolin production upon different types of stress have been described (Schenke et al ., ). An indirect effect on scopolin accumulation was proposed for the TFs BRASSINOSTEROID ENHANCED EXPRESSION1 (BEE1) and G2‐LIKE FLAVONOID REGULATOR (GFR), while suppressing TFs for anthocyanin biosynthesis (Petridis et al ., ).…”

Epigenetic regulation of anthocyanin biosynthesis by an antagonistic interaction between H2A.Z and H3K4me3

“…The expression of the genes involved in the late stages of anthocyanin biosynthesis, including ANTHOCYANIDIN SYNTHASE ( ANS ), DIHYDROFLAVONOL REDUCTASE ( DFR ), FLAVONOIN 3′‐HYDROXYLASE ( F3′H ), LEUCOANTHOCYANIN DIOXYGENASE ( LDOX ), UDP‐GLUCOSYLTRANSFERASE78D2 ( UGT78D2 ) and UDP‐GLUCOSYLTRANSFERASE75C1 ( UGT75C1 ), is positively regulated by the MBW complex, a transcriptional activation complex composed of basic helix‐loop‐helix (bHLH), R2R3‐MYB and WD‐repeat (WDR) proteins (Baudry et al ., ; Hartmann et al ., ; Ramsay & Glover, ; Gonzalez et al ., ). Many negative regulators of anthocyanin biosynthesis have also been identified, such as MYBL2 and MYB27 (in Petunia ), and LATERAL ORGAN BOUNDARY DOMAIN (LBD37, LBD38 and LBD39), SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE9 (SPL9), BRASSINOSTEROID ENHANCED EXPRESSION1 (BEE1) and G2‐LIKE FLAVONOID REGULATOR (GFR) (in Arabidopsis ) (Dubos et al ., ; Matsui et al ., ; Rubin et al ., ; Gou et al ., ; Albert et al ., ; Petridis et al ., ).…”

“…2004; Hartmann et al, 2005;Ramsay & Glover, 2005;Gonzalez et al, 2008). Many negative regulators of anthocyanin biosynthesis have also been identified, such as MYBL2 and MYB27 (in Petunia), and LATERAL ORGAN BOUNDARY DOMAIN (LBD37, LBD38 and LBD39), SQUAMOSA PROMOTER BINDING PROTEIN-LIKE9 (SPL9), BRASSINOSTEROID ENHANCED EXPRESSION1 (BEE1) and G2-LIKE FLAVONOID REGULATOR (GFR) (in Arabidopsis) (Dubos et al, 2008;Matsui et al, 2008;Rubin et al, 2009;Gou et al, 2011;Albert et al, 2014;Petridis et al, 2016).…”