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.