The TT8 Gene Encodes a Basic Helix-Loop-Helix Domain Protein Required for Expression of DFR and BAN Genes in Arabidopsis Siliques

Abstract

The TRANSPARENT TESTA8 (TT8) locus is involved in the regulation of flavonoid biosynthesis in Arabidopsis. The tt8-3 allele was isolated from a T-DNA-mutagenized Arabidopsis collection and found to be tagged by an integrative molecule, thus permitting the cloning and sequencing of the TT8 gene. TT8 identity was confirmed by complementation of tt8-3 and sequence analysis of an additional allele. The TT8 gene encodes a protein that displays a basic helix-loop-helix at its C terminus and represents an Arabidopsis ortholog of the maize R transcription factors. The TT8 transcript is present in developing siliques and in young seedlings. The TT8 protein is required for normal expression of two flavonoid late biosynthetic genes, namely, DIHYDROFLAVONOL 4-REDUCTASE (DFR) and BANYULS (BAN), in Arabidopsis siliques. Interestingly, TRANSPARENT TESTA GLABRA1 (TTG1) and TT2 genes also control the expression of DFR and BAN genes. Our results suggest that the TT8, TTG1, and TT2 proteins may interact to control flavonoid metabolism in the Arabidopsis seed coat.

On plant defense signaling networks and early land plant evolution

“…A 1969 study by Markham and Porter [155] reported on the presence of flavonoids in the charophyceae Nitella , highlighting the need to further investigate streptophyte algae with regard to the presence of these metabolites. It is noteworthy that Van de Poel and colleagues [115] found ET-dependent regulation of a homolog of TRANSPARENT TESTA 8 ( TT8 ) in the Zygnematophyceae Spirogyra pratensis ; TT8 is a known regulator of flavonoid biosynthesis [156]. A TT8 ortholog is also present in the dataset for the Coleochaetophyceae Coleochaete scutata [114], where it is induced by high light stress.…”

Sugar-Hormone Cross-Talk in Anthocyanin Biosynthesis

“…Transcription factors from the R2R3-MYB, bHLH and WD40 classes interact to form MBW regulatory complexes (Borevitz et al, 2000;Gonzalez et al, 2008;Tohge et al, 2005;Zhang et al, 2003). For instance, TRANSPARENT TESTA 2 (TT2; MYB123) requires the cofactors TT8 (bHLH42) and TTG1 (WD40-repeat protein) to form a ternary MBW complex that regulates the expression of the DFR and ANR genes, which are involved in the accumulation of proanthocyanidins in the seed coat (Baudry et al, 2004;Nesi et al, 2000;. Similarly, MYB75/PAP1 (PRODUCTION OF ANTHOCYANIN PIGMENT1) and MYB90/PAP2, which are members of the R2R3-MYB family, are responsible for bHLH co-factor-dependent transcriptional activation of phenylalanine-ammonia lyase (PAL), CHS, DFR and glutathione-S-transferase (GST), which are key enzymes of the anthocyanin biosynthesis pathway (Hichri et al, 2011).…”

Characterization of EMU, the Arabidopsis homolog of the yeast THO complex member HPR1

“…The gene-specific primers used were 5g09860-FW4 (59-AGCATATACTGGAGCGCG-39) and 5g09860-RV2 (59-AGCTAGCAGATTTGCACTC-39) for EMU. Primers for SR genes, EF1aA4, and TUB2 were previously described (Lee et al 2000;Nesi et al 2000;Palusa et al 2007). The PCR program started at 94°C for 2 min, followed by the optimum number of cycles of 30 sec at 94°C, 30 sec at 56°C, and 1 min at 68°C.…”