The strawberry FaMYB1 transcription factor suppresses anthocyanin and flavonol accumulation in transgenic tobacco

Abstract

SummaryFruit ripening is characterized by dramatic changes in gene expression, enzymatic activities and metabolism. Although the process of ripening has been studied extensively, we still lack valuable information on how the numerous metabolic pathways are regulated and co-ordinated. In this paper we describe the characterization of FaMYB1, a ripening regulated strawberry gene member of the MYB family of transcription factors. Flowers of transgenic tobacco lines overexpressing FaMYB1 showed a severe reduction in pigmentation. A reduction in the level of cyanidin 3-rutinoside (an anthocyanin) and of quercetin-glycosides (¯avonols) was observed. Expression of late¯avonoid biosynthesis genes and their enzyme activities were aversely affected by FaMYB1 overexpression. Two-hybrid assays in yeast showed that FaMYB1 could interact with other known anthocyanin regulators, but it does not act as a transcriptional activator. Interestingly, the C-terminus of FaMYB1 contains the motif pdLNL D / E Lxi G / S . This motif is contained in a region recently proposed to be involved in the repression of transcription by AtMYB4, an Arabidopsis MYB protein. Our results suggest that FaMYB1 may play a key role in regulating the biosynthesis of anthocyanins and¯avonols in strawberry. It may act to repress transcription in order to balance the levels of anthocyanin pigments produced at the latter stages of strawberry fruit maturation, and/or to regulate metabolite levels in various branches of the¯avonoid biosynthetic pathway.

The MYB182 Protein Down-Regulates Proanthocyanidin and Anthocyanin Biosynthesis in Poplar by Repressing Both Structural and Regulatory Flavonoid Genes

“…As expected, clades for known anthocyanin, flavonol, and two types of PA activators (TT2 and MYBPA1 types) were clearly defined with strong bootstrap support. The new poplar repressor MYBs grouped together with the previously characterized anthocyanin repressors FaMYB1 and PhMYB27 from strawberry and petunia and the PA repressor VvMYBC2-L1 from grapevine (Aharoni et al, 2001;Albert et al, 2014;Huang et al, 2014). This subclade was separated from the second major group of R2R3 repressor MYBs that comprises the general phenylpropanoid and lignin repressors from a variety of plants, including monocots.…”

“…These include strawberry FaMYB1 and FcMYB1 (for Fragaria chiloensis) and petunia PhMYB27 (Aharoni et al, 2001;Salvatierra et al, 2013;Albert et al, 2014). Overexpression of FaMYB1 causes the suppression of anthocyanin synthesis in tobacco (Nicotiana tabacum), and suppression of FcMYB1 by transient RNA interference in strawberry fruit increased the accumulation of anthocyanin.…”

“…Likewise, RNA interference suppression of PhMYB27 increases the accumulation of anthocyanin in petunia flowers and vegetative tissues (Albert et al, 2014). In phylogenies, these flavonoid R2R3 repressor MYBs all cluster together within MYB subgroup 4 (Stracke et al, 2001), and all share the C2 motif (pfLNLD/ ELxiG/S) with a core consensus sequence of LxLxL or DLNxxP (Aharoni et al, 2001;Dubos et al, 2010). These consensus sequences are the signature patterns of the EAR (for ethylene-responsive factor [ERF]-associated amphiphilic repression) motif, the predominant form of transcriptional repressor motif identified in plants ( Kagale and Rozwadowski, 2011).…”

“…For example, FaMYB1 suppresses anthocyanin biosynthetic genes when overexpressed in tobacco, including ANS and UGT (Aharoni et al, 2001), and MYBL2 targets CHS, chalcone isomerase (CHI), F3H, DFR, ANS, and TT8 (Dubos et al, 2008;Matsui et al, 2008). However, when overexpressed in Lotus corniculatus, FaMYB1 also reduces PA biosynthesis (Paolocci et al, 2011), and AtMYBL2 suppresses ANR expression in the seed coat (Dubos et al, 2008).…”

Cloning and characterization of a glucosyltransferase that reacts on 7-hydroxyl group of flavonol and 3-hydroxyl group of coumarin from tobacco cells

“…Considering the fact that NTGT2 is very similar to A5GT in terms of the primary structure (Fig 1), we tested its activity against cyanidin and cyanidin-3-O-glucoside, which are naturally occurring anthocyanins (about > 90%) in tobacco flowers [26]. The rNTGT2 enzyme hardly reacted on the compounds under conditions that would be favorable for other A5GTs.…”