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

Abstract

MtPAR (Medicago truncatula proanthocyanidin regulator) is an MYB family transcription factor that functions as a key regulator of proanthocyanidin (PA) biosynthesis in the model legume Medicago truncatula. MtPAR expression is confined to the seed coat, the site of PA accumulation. Loss-of-function par mutants contained substantially less PA in the seed coat than the wild type, whereas levels of anthocyanin and other specialized metabolites were normal in the mutants. In contrast, massive accumulation of PAs occurred when MtPAR was expressed ectopically in transformed hairy roots of Medicago. Transcriptome analysis of par mutants and MtPAR-expressing hairy roots, coupled with yeast one-hybrid analysis, revealed that MtPAR positively regulates genes encoding enzymes of the flavonoid-PA pathway via a probable activation of WD40-1. Expression of MtPAR in the forage legume alfalfa (Medicago sativa) resulted in detectable levels of PA in shoots, highlighting the potential of this gene for biotechnological strategies to increase PAs in forage legumes for reduction of pasture bloat in ruminant animals.condensed tannin | forage quality | metabolic engineering

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

“…and alfalfa, consistent with our result that MtMYB14 is able to promote PA accumulation in M. truncatula hairy roots. MtPAR, another TT2-related MYB transcription factor in M. truncatula, also promotes PA accumulation in M. truncatula hairy roots and alfalfa plants (Verdier et al, 2012). PA accumulation is also induced by strong expression of Arabidopsis TT2 in M. truncatula hairy roots (Pang et al, 2008).…”

“…Recently, we discovered that another M. truncatula MYB transcription factor, PAR, also regulates PA biosynthesis in the M. truncatula seed coat (Verdier et al, 2012). Unlike loss of function of MYB5 and MYB14, the par mutant exhibits a lighter seed coat color than the wild type, indicating that PAR either regulates both anthocyanin and PA biosynthesis or does not negatively regulate the anthocyanin pathway.…”

“…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).…”

“…The M. truncatula WD40-1 promoter reporter yeast (Saccharomyces cerevisiae) strain was generated as described by Verdier et al (2012). A cDNA library was constructed from RNAs of 10-DAP seeds of M. truncatula A17 using the CloneMiner II cDNA Library Construction Kit (Invitrogen).…”

MYB transcription factor genes as regulators for plant responses: an overview

“…Stracke et al (2007) found that AtMYB11/PFG1, AtMYB12/PFG1 and AtMYB111/PFG3 controled flavones biosynthesis in all tissues while AtMYB75/ PAP1, AtMYB90/PAP2, AtMYB113 and AtMYB114 regulated anthocyanin biosynthesis in vegetative tissues (Gonzalez et al 2008) while AtMYB123/TT2 controlled the biosynthesis of proanthocyanidins (PAs) in the seed coat of Arabidopsis (Lepiniec et al 2006). Verdier et al (2012). Found that MtPAR (Medicago truncatula proanthocyanidin regulator) was a MYB family transcription factor that functioned as a key regulator of proanthocyanidin (PA) biosynthesis in the model legume Medicago truncatula and could be of great potential for biotechnological strategies to increase PAs in forage legumes for reduction of pasture bloat in ruminant animals.…”