Résumé
Flavonoids are secondary metabolites that fulfil a multitude of functions during the plant life cycle. In Arabidopsisproanthocyanidins (PAs) are flavonoids that specifically accumulate in the innermost integuments of the seedtesta (i.e. endothelium), as well as in the chalaza and micropyle areas, and play a vital role in protecting the embryoagainst various biotic and abiotic stresses. PAs accumulation in the endothelium requires the activity of the MADSbox transcription factor TRANSPARENT TESTA (TT) 16 (ARABIDOPSIS B-SISTER/AGAMOUS-LIKE 32) and the UDPglycosyltransferaseTT15 (UGT80B1). Interestingly tt16 and tt15 mutants display a very similar flavonoid profiles andpatterns of PA accumulation. By using a combination of genetic, molecular, biochemical, and histochemical methods,we showed that both TT16 and TT15 act upstream the PA biosynthetic pathway, but through two distinct geneticroutes. We also demonstrated that the activity of TT16 in regulating cell fate determination and PA accumulation in theendothelium is required in the chalaza prior to the globular stage of embryo development. Finally this study providesnew insight showing that TT16 and TT15 functions extend beyond PA biosynthesis in the inner integuments of theArabidopsis seed coat.