A WD40 Repeat Protein fromMedicago truncatulaIs Necessary for Tissue-Specific Anthocyanin and Proanthocyanidin Biosynthesis But Not for Trichome Development    

Abstract

WD40 repeat proteins regulate biosynthesis of anthocyanins, proanthocyanidins (PAs), and mucilage in the seed and the development of trichomes and root hairs. We have cloned and characterized a WD40 repeat protein gene from Medicago truncatula (MtWD40-1) via a retrotransposon-tagging approach. Deficiency of MtWD40-1 expression blocks accumulation of mucilage and a range of phenolic compounds, including PAs, epicatechin, other flavonoids, and benzoic acids, in the seed, reduces epicatechin levels without corresponding effects on other flavonoids in flowers, reduces isoflavone levels in roots, but does not impair trichome or root hair development. MtWD40-1 is expressed constitutively, with highest expression in the seed coat, where its transcript profile temporally parallels those of PA biosynthetic genes. Transcript profile analysis revealed that many genes of flavonoid biosynthesis were down-regulated in a tissue-specific manner in M. truncatula lines harboring retrotransposon insertions in the MtWD40-1 gene. MtWD40-1 complemented the anthocyanin, PA, and trichome phenotypes of the Arabidopsis (Arabidopsis thaliana) transparent testa glabrous1 mutant. We discuss the function of MtWD40-1 in natural product formation in M. truncatula and the potential use of the gene for engineering PAs in the forage legume alfalfa (Medicago sativa).

MtPAR MYB transcription factor acts as an on switch for proanthocyanidin biosynthesis in Medicago truncatula

“…Previously, a WD40 repeat protein, orthologous to Arabidopsis TTG1, was identified in M. truncatula and called MtWD40-1 (15). M. truncatula wd40-1 mutants display a drastic decrease of soluble and insoluble PA (15). However, overexpression of MtWD40-1 in M. truncatula hairy roots results in an increase of anthocyanin concentration without affecting PA concentration.…”

“…Previously, a WD40 repeat protein, orthologous to Arabidopsis TTG1, was identified in M. truncatula and called MtWD40-1 (15). M. truncatula wd40-1 mutants display a drastic decrease of soluble and insoluble PA (15).…”

“…However, relatively little is known about the regulation of PA biosynthesis in M. truncatula and other legumes; only a WD40-repeat TF has been implicated as a positive regulator of PA biosynthesis in M. truncatula seeds (15).…”

MYB5 and MYB14 Play Pivotal Roles in Seed Coat Polymer Biosynthesis in Medicago truncatula

“…A WD-40 protein is a key component of the transcriptional complex that activates PA biosynthetic genes (Lepiniec et al, 2006;Pang et al, 2009), and we recently reported that the MYB transcription factor MtPAR (for proanthocyanidin regulator) can activate the promoter of M. truncatula WD40-1 in yeast (Saccharomyces cerevisiae; Verdier et al, 2012). To search for new positive regulators of WD40-1, which may also play a role in PA biosynthesis, we performed a yeast one-hybrid (Y1H) screen against a complementary DNA (cDNA) library of young seeds harvested at 10 d after pollination (DAP).…”

Functional genomics to study stress responses in crop legumes: progress and prospects

“…affymetrix.com/estore/browse/products.jsp?productId=131507 #1_1, accessed 29 May 2013). Several studies in model legumes have employed these GeneChip Genome Arrays for research into developmental or metabolic pathways (Pang et al 2009;Verdier et al 2013). In the case of soybean, the GeneChip Soybean Genome Array permitted the characterisation of genome-wide expression patterns, and identified drought-responsive candidate genes.…”