Plant age-dependent dynamics of annatto pigment (bixin) biosynthesis inBixa orellanaL.

Abstract

SummaryAge affects the production of secondary metabolites, but how developmental cues regulate secondary metabolism remains poorly understood. Annatto(Bixa orellanaL.) is a source of bixin, an apocarotenoid used in the world’s food industry worldwide. Understanding how age-dependent mechanisms control bixin biosynthesis is of great interest for plant biology and for pharmaceutical, cosmetic, and textile industries. Here, we used genetic and molecular tools to unravel the role of the annatto age regulated miRNA156 (miR156) targetedSQUAMOSA PROMOTER BINDING PROTEIN LIKE (BoSPL)genes in secondary metabolism. Low expression of severalBoSPLgenes in miR156 overexpressing annatto plants (OE::156) impacted leaf ontogeny, reducing bixin production and increasing abscisic acid (ABA) levels. Modulation ofBoCCD4;4andBoCCD1expression, key genes in lycopene cleavage, was associated with diverting the carbon flux from bixin to ABA, whereas upregulation oflycopene β cyclasegenes implies the xanthophyll biosynthetic pathway acted as a carbon sink in OE::156 plants. Proteomic analyses revealed low accumulation of most secondary metabolite-related enzymes in OE::156 plants, suggesting that miR156 targetedBoSPLsare required to activate several annatto secondary metabolic pathways. Our findings suggest that carbon flux inB. orellanaOE::156 leaves was redirected from bixin to ABA production, indicating an age-dependent leaf dynamics of bixin biosynthesis. Importantly, our study opened a new venue to future annatto breeding programs aiming to improve bixin output.