The Arabidopsis TT2 Gene Encodes an R2R3 MYB Domain Protein That Acts as a Key Determinant for Proanthocyanidin Accumulation in Developing Seed

Abstract

In Arabidopsis, proanthocyanidins specifically accumulate in the endothelium during early seed development. At least three TRANSPARENT TESTA (TT) genes, TT2 , TT8 , and TTG1 , are necessary for the normal expression of several flavonoid structural genes in immature seed, such as DIHYDROFLAVONOL-4-REDUCTASE and BANYULS (BAN). TT8 and TTG1 were characterized recently and found to code for a basic helix-loop-helix domain transcription factor and a WDrepeat-containing protein, respectively. Here the molecular cloning of the TT2 gene was achieved by T-DNA tagging. TT2 encoded an R2R3 MYB domain protein with high similarity to the rice OsMYB3 protein and the maize COLORLESS1 factor. A TT2-green fluorescent protein fusion protein was located mostly in the nucleus, in agreement with the regulatory function of the native TT2 protein. TT2 expression was restricted to the seed during early embryogenesis, consistent with BAN expression and the proanthocyanidin deposition profile. Finally, in gain-of-function experiments, TT2 was able to induce ectopic expression of BAN in young seedlings and roots in the presence of a functional TT8 protein. Therefore, our results strongly suggest that stringent spatial and temporal BAN expression, and thus proanthocyanidin accumulation, are determined at least partially by TT2.

De Novo transcriptome characterization of Dracaena cambodiana and analysis of genes involved in flavonoid accumulation during formation of dragon’s blood

“…Moreover, TFs also control the regulation of flavonoid transport. For example, AtTT2 regulates the expression of the MATE transporter gene TT12 to control the flavonoids transport41, and the maize ABC transporter ZmMRP3 involved in anthocyanin transport is regulated by the R (bHLH family) and C1 (R2R3-MYB) TFs35; and anthocyanin-related glutathione S-transferase gene LcGST4 was activated by LcMYB1, a key R2R3-MYB transcription factor that regulates anthocyanin biosynthesis in litchi35. Most of TFs are positive regulators in flavonoid biosynthesis, whereas a few of them have been identified as repressors in flavonoid pathway42.…”

Genome-Wide Survey of Flavonoid Biosynthesis Genes and Gene Expression Analysis between Black- and Yellow-Seeded Brassica napus

“…and Late Biosynthetic Genes ( BAN, DFR , and TTG1 , etc.) (Nesi et al, 2000, 2001; Winkel-Shirley, 2001; Lepiniec et al, 2006). Homologs of some of these genes, named TT –type genes, have also been identified and shown to be involved in the flavonoid biosynthetic pathway.…”

“…In plant kingdom, flavonoid biosynthesis pathway play important roles in the coloration of fruits, flowers, and seeds, and numerous evidences had showed that TT -type genes and their homologs are crucial for the accumulation of flavonoids and their derivatives (Nesi et al, 2001; Winkel-Shirley, 2002; Xie et al, 2003; Baudry et al, 2004; Hoffmann et al, 2006; Lepiniec et al, 2006; Kasai et al, 2007). In the model plant Arabidopsis thaliana , the formation of transparent and colorless testa (seed coat) were associated with tt loci that are disrupted the flavonoid synthesis pathway in the loss-of-function mutations (Wan et al, 2002; Winkel-Shirley, 2002; Baudry et al, 2004; Lepiniec et al, 2006).…”

“…In the model plant Arabidopsis thaliana , the formation of transparent and colorless testa (seed coat) were associated with tt loci that are disrupted the flavonoid synthesis pathway in the loss-of-function mutations (Wan et al, 2002; Winkel-Shirley, 2002; Baudry et al, 2004; Lepiniec et al, 2006). To date, 17 genes involved in this pathway have been cloned and functionally characterized, including eight structural genes (i.e., TT3, TT4, TT5, TT6, TT7, FLS1, LDOX , and BAN ; Albert et al, 1997; Devic et al, 1999; Xie et al, 2003; Routaboul et al, 2006; Chiu et al, 2010), six regulatory genes ( TT1, TT2, TT8, TTG1, TTG2 , and TT16 ; Nesi et al, 2000, 2001; Baudry et al, 2006; Routaboul et al, 2006), and three encoding transfer proteins ( TT12, TT19 , and AHA10 ; Debeaujon et al, 2001; Baxter et al, 2005), which were also classified as Early Biosynthetic Genes ( CHS, CHI , and F3H etc.) and Late Biosynthetic Genes ( BAN, DFR , and TTG1 , etc.)…”

AthaMap web tools for database-assisted identification of combinatorial cis-regulatory elements and the display of highly conserved transcription factor binding sites in Arabidopsis thaliana

“…Hence, annotated bZIP sites were employed for the identification of MYC-binding sites in combinatorial elements. The identification of functional MYC/MYB-binding sites by employing bZIP sites can be shown for the gene encoding BANYULS that is induced by the interacting TFs TT8 (MYC) and TT2 (MYB) (16,22,23). When the Arabidopsis genome identification number of the Banyuls gene (AT1G61720.1) is used for a search in the AthaMap database, a putative MYC/MYB combinatorial element is detected upstream of the TATA-box (data not shown).…”