Ethylene Suppression of Sugar-Induced Anthocyanin Pigmentation in Arabidopsis

Abstract

Anthocyanin accumulation is regulated negatively by ethylene signaling and positively by sugar and light signaling. However, the antagonistic interactions underlying these signalings remain to be elucidated fully. We show that ethylene inhibits anthocyanin accumulation induced by sucrose (Suc) and light by suppressing the expression of transcription factors that positively regulate anthocyanin biosynthesis, including GLABRA3, TRANSPARENT TESTA8, and PRODUCTION OF AN-THOCYANIN PIGMENT1, while stimulating the concomitant expression of the negative R3-MYB regulator MYBL2. Genetic analyses show that the ethylene-mediated suppression of anthocyanin accumulation is dependent upon ethylene signaling components responsible for the triple response. Furthermore, these positive and negative signaling pathways appear to be under photosynthetic control. Suc and light induction of anthocyanin accumulation was almost fully inhibited in wild-type Arabidopsis (Arabidopsis thaliana) ecotype Columbia and ethylene (ethylene response1 [etr1-1]) and light (long hypocotyl1 [hy1], cryptochrome1/2, and hy5) signaling mutants treated with the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The transcript level of the sugar transporter gene SUC1 was enhanced in ecotype Columbia treated with the ethylene-binding inhibitor silver and in etr1-1, ethylene insensitive2 (ein2-1), and ein3 ein3-like1 mutants. In contrast, 3-(3,4-dichlorophenyl)-1,1-dimethylurea treatment reduced SUC1 expression, which indicates strongly that SUC1 represents an integrator for signals provided by sugar, light, and ethylene. SUC1 mutations lowered accumulations of anthocyanin pigment, soluble sugar content, and ethylene production in response to Suc and light signals. These data demonstrate that the suppression of SUC1 expression by ethylene inhibits Suc-induced anthocyanin accumulation in the presence of light and, hence, fine-tunes anthocyanin homeostasis.Anthocyanins play key roles in many plant physiological processes; for instance, they form photoprotective screens in vegetative tissue, act as visual attractors to aid pollination and seed dispersal, and function as antimicrobial agents and feeding deterrents in the defense response (Winkel-Shirley, 2001;Steyn et al., 2002). The anthocyanin biosynthetic pathway is well described in plants. In Arabidopsis (Arabidopsis thaliana) and other plants, including Antirrhinum majus (snapdragon) and Petunia hybrida (petunia), early biosynthesis genes (EBGs) such as chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), and flavonoid 3#-hydroxylase (F3#H), which are common to different flavonoid subpathways, are induced prior to late biosynthesis genes (LBGs) such as dihydroflavonol 4-reductase (DFR), leucoanthocyanidin oxygenase (LDOX), anthocyanidin reductase (ANR), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UF3GT; Pelletier et al., 1997). EBGs and LBGs are transcriptionally activated by R2R3-MYBs, such as PRODUCTION OF ANTHOCYANIN PIG-MENT1 (PAP1) a...

Sugar-Hormone Cross-Talk in Anthocyanin Biosynthesis

“…Furthermore, SUC1 expression and anthocyanin accumulation differ with respect to sugar specificity; anthocyanin synthesis is preferentially induced by the metabolizable disaccharides Suc and Mal, while SUC1 expression can be induced effectively by monosaccharide sugars such as Glc and Fru in addition to Suc and Mal (Jeong et al, 2010). There are no apparent differences between the induction of SUC1 expression by sugars and the osmoticums mannitol and palatinose (Jeong et al, 2010), indicating that SUC1 expression requires the presence of an osmotic sensor rather than membrane or intracellular receptors. AtSUC1 seems to play a role in Suc uptake rather than acting as a sugar sensor for anthocyanin production.…”

“…Exogenous Suc increased the transcript levels of the LBGs DFR, LDOX and UF3GT by several hundred-fold, while the transcripts levels of EBGs acting upstream of the DFR in anthocyanin biosynthesis, including CHI, CHS, and C4H, showed lower induction by Suc. This Suc effect on the induction of anthocyanin biosynthetic genes may be attributed to the greater than 2-fold upregulation of positive TFs such as GL3, TT8 and PAP1 concurrent with the 3.3-fold downregulation of the negative transcription factor MYBL2 (Jeong et al, 2010). Under these conditions, the active MBW complex would be dominant over the negative L2BW complex.…”

“…This view was supported by a recent report showing that suc1-defective mutants grown in 3% but not in 5% Suc-containing growth medium had diminished anthocyanin accumulation (Sivitz et al, 2008). However, SUC1 expression and anthocyanin accumulation are spatially separated; SUC1 is expressed preferentially in the roots (Sivitz et al, 2008), while anthocyanin accumulates predominantly in the sub-epidermal cell layers of leaves (Jeong et al, 2010;Kubo et al, 1999). Furthermore, SUC1 expression and anthocyanin accumulation differ with respect to sugar specificity; anthocyanin synthesis is preferentially induced by the metabolizable disaccharides Suc and Mal, while SUC1 expression can be induced effectively by monosaccharide sugars such as Glc and Fru in addition to Suc and Mal (Jeong et al, 2010).…”

“…However, SUC1 expression and anthocyanin accumulation are spatially separated; SUC1 is expressed preferentially in the roots (Sivitz et al, 2008), while anthocyanin accumulates predominantly in the sub-epidermal cell layers of leaves (Jeong et al, 2010;Kubo et al, 1999). Furthermore, SUC1 expression and anthocyanin accumulation differ with respect to sugar specificity; anthocyanin synthesis is preferentially induced by the metabolizable disaccharides Suc and Mal, while SUC1 expression can be induced effectively by monosaccharide sugars such as Glc and Fru in addition to Suc and Mal (Jeong et al, 2010). There are no apparent differences between the induction of SUC1 expression by sugars and the osmoticums mannitol and palatinose (Jeong et al, 2010), indicating that SUC1 expression requires the presence of an osmotic sensor rather than membrane or intracellular receptors.…”

“…However, the signaling pathways triggered by sugars, hormones and light and the interactions between these signals, if any, are not well understood. A recent finding that the photosynthetic electron transport (PET) chain, in addition to the well-characterized HY5-dependent signaling, plays an important role in light signaling pathways in green, vegetative leaf tissues (Das et al, 2011;Jeong et al, 2010) demonstrates the complexity of the cross-talk between various pathways. Sugar-induced anthocyanin biosynthesis is apparently modulated by the heterotrimeric M(L2)BW complexes that are under the regulation of hormones (Das et al, 2012;Jeong et al, 2010;Loreti et al, 2008;Shan et al, 2009), Fig.…”