TRANSPARENT TESTA GLABRA 1-Dependent Regulation of Flavonoid Biosynthesis

Abstract

The flavonoid composition of various tissues throughout plant development is of biological relevance and particular interest for breeding. Arabidopsis thaliana TRANSPARENT TESTA GLABRA 1 (AtTTG1) is an essential regulator of late structural genes in flavonoid biosynthesis. Here, we provide a review of the regulation of the pathway’s core enzymes through AtTTG1-containing R2R3-MYELOBLASTOSIS-basic HELIX-LOOP-HELIX-WD40 repeat (MBW(AtTTG1)) complexes embedded in an evolutionary context. We present a comprehensive collection of A. thaliana ttg1 mutants and AtTTG1 orthologs. A plethora of MBW(AtTTG1) mechanisms in regulating the five major TTG1-dependent traits is highlighted.

Novel TTG1 Mutants Modify Root-Hair Pattern Formation in Arabidopsis

“…Our finding that the ttg1-23 and ttg1-24 mutations enhance the cpc-1 phenotype (i.e., increase the production of non-hair cells) was unexpected, because previous studies have shown that ttg1 mutants produce more root-hair cells and thus TTG1 is likely involved in non-hair cell specification (Galway et al, 1994). To investigate this discrepancy, we examined additional mutant alleles of the TTG1 gene which have not been analyzed in detail for their root-hair phenotypes (Zhang and Schrader, 2017). We selected three previously described ttg1 mutant lines: ttg1-1, ttg1-9, and ttg1-13.…”

“…In addition to root-hair patterning, the TTG1 gene is involved in several other developmental and biochemical pathways in Arabidopsis including trichome patterning, anthocyanin accumulation, seed coat pigmentation, and seed mucilage production (Walker et al, 1999;Miller et al, 2016). For each pathway, TTG1 appears to participate via a MBW complex, although different MYB and bHLH components are used for the five pathways (Zhang and Schrader, 2017). In trichome patterning, GLABROUS1 (GL1) is functionally equivalent to WER and forms a GL1-GL3/EGL3-TTG1 complex to promote trichome differentiation (Larkin et al, 1999;Kirik et al, 2005).…”

“…The TTG1 gene encodes a protein of 341 amino acid residues with four WD40 repeats (Walker et al, 1999), and many ttg1 alleles have been identified, such as ttg1-1 (Q317stop) (Koornneef, 1981), ttg1-9 (S282F) (Larkin et al, 1994b), ttg1-10 (G→A in 5'UTR) (Larkin et al, 1994a), and ttg1-13 (deletion) (Larkin et al, 1999). These mutant lines exhibit pleiotropic phenotypes, including excessive (ectopic) root hairs, glabrous leaves, and yellow seed coat, although the severity of the mutant alleles varies (Bouyer et al, 2008;Zhang and Schrader, 2017).…”

Genome-wide transcriptome profiling of transgenic hop (Humulus lupulus L.) constitutively overexpressing HlWRKY1 and HlWDR1 transcription factors

“…The Hl WRKY1 and Hl WDR1 transcription factors are preferentially expressed in lupulin glands, function as a master regulator to drive the PF and BA biosynthesis pathways [ 18 , 19 ]. The homologs of these two transcription factors have multifunctional roles [ 21 , 22 ]. In this context, it was imperative to understand whether constitutive expression of these two transcription factors could serve as an important strategy to enhance the PF and BA content by analyzing overall impact over the morphological, developmental attributes and other related pathways of hop.…”

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“…PRR5 recruits TTG1 to subnuclear foci and bHLH92 nuclear enrichment is counteracted by TTG1. In its role as a regulator of early (accessible) developmental traits, TTG1 acts through differential complex composition, in competitive scenarios and is for example trapped by the bHLH factor GL3 in the nucleus of developing trichomes (Balkunde et al 2011;Bouyer et al 2008;Pesch et al 2015;Wester et al 2009;Zhang et al 2019;Zhang & Schrader 2017;Zhao et al 2008). All these scenarios occur at the protein level in dependence of its interactors.…”