Ectopic Expression of the Coleus R2R3 MYB-Type Proanthocyanidin Regulator Gene SsMYB3 Alters the Flower Color in Transgenic Tobacco

Abstract

Proanthocyanidins (PAs) play an important role in plant disease defense and have beneficial effects on human health. We isolated and characterized a novel R2R3 MYB-type PA-regulator SsMYB3 from a well-known ornamental plant, coleus (Solenostemon scutellarioides), to study the molecular regulation of PAs and to engineer PAs biosynthesis. The expression level of SsMYB3 was correlated with condensed tannins contents in various coleus tissues and was induced by wounding and light. A complementation test in the Arabidopsis tt2 mutant showed that SsMYB3 could restore the PA-deficient seed coat phenotype and activated expression of the PA-specific gene ANR and two related genes, DFR and ANS. In yeast two-hybrid assays, SsMYB3 interacted with the Arabidopsis AtTT8 and AtTTG1 to reform the ternary transcriptional complex, and also interacted with two tobacco bHLH proteins (NtAn1a and NtJAF13-1) and a WD40 protein, NtAn11-1. Ectopic overexpression of SsMYB3 in transgenic tobacco led to almost-white flowers by greatly reducing anthocyanin levels and enhancing accumulation of condensed tannins. This overexpression of SsMYB3 upregulated the key PA genes (NtLAR and NtANR) and late anthocyanin structural genes (NtDFR and NtANS), but downregulated the expression of the final anthocyanin gene NtUFGT. The formative SsMYB3-complex represses anthocyanin accumulation by directly suppressing the expression of the final anthocyanin structural gene NtUFGT, through competitive inhibition or destabilization of the endogenous NtAn2-complex formation. These results suggested that SsMYB3 may form a transcription activation complex to regulate PA biosynthesis in the Arabidopsis tt2 mutant and transgenic tobacco. Our findings suggest that SsMYB3 is involved in the regulation of PA biosynthesis in coleus and has the potential as a molecular tool for manipulating biosynthesis of PAs in fruits and other crops using metabolic engineering.

The Analysis of Physiological Variations in M2 Generation of Solanum melongena L. Mutagenized by Ethyl Methane Sulfonate

“…Several results indicated that MYB and bHLH transcriptional factor families play a vital role in the regulation of tissue color (Umemura et al, 2013; Zhu et al, 2015). Gisbert et al (2016) showed that the regulatory genes ( MybC, Myc, and Wd ) was significantly decreased in the green color mutant in comparison with the WT eggplant.…”

Benefits of Condensed Tannins in Forage Legumes Fed to Ruminants: Importance of Structure, Concentration, and Diet Composition

“…The benefits of CTs have been demonstrated in only support the primary plant metabolism (Haslam, 1981). It is now well established that CT synthesis is under genetic control (Szczyglowski and Stougaard, 2008;Scioneaux et al, 2011;Cheynier et al, 2013;Escaray et al, 2014) and that expression depends on the plant species and plant parts (Larkin et al, 1997;Gebrehiwot et al, 2002;Abeynayake et al, 2012;Ferreyra et al, 2012;Hancock et al, 2012;Verdier et al, 2012;Cheynier et al, 2013;Harding et al, 2013;Mouradov and Spangenberg, 2014;Pérez-Díaz et al, 2014;Zhou et al, 2015;Zhu et al, 2015;Chezem and Clay, 2016).…”

“…All enzymes involved in the biosynthesis of the CT building blocks (i.e., flavan-3-ols) have been identified, apart from the elusive final condensing enzyme(s) (Harding et al, 2013). Two genes and several myeloblastosis (MYB) transcription factors (i.e., proteins with myeloblastosis DNAbinding domains that regulate CT synthesis) are responsible for the production of two of the flavan-3-ols (i.e., catechin and epicatechin; Ferreyra et al, 2012;Cheynier et al, 2013;Zhu et al, 2015;Chezem and Clay, 2016), but the genes and transcription factors for the other flavan-3-ols await identification. The MYB transcription factors from barrelclover (Medicago truncatula Gaertn.)…”

Why Are There so Many Plant Species That Transiently Flush Young Leaves Red in the Tropics?

“…The relative concentration of anthocyanins was determined following Christie et al (1994) and Zhu et al (2015) with minor modifications. Pulverized leaf blade tissue (1.0 g fresh weight) was homogenized in 12 ml of methanol containing 0.1 N HCL and maintained at 4°C for 4 h. Three repetitions were performed for each taxon.…”