Accumulation of azafrin in the root apoplast of the medicinal plant Escobedia grandiflora might play a role in parasitism

Societal Impact Statement: Escobedia grandiflora is a medicinal hemiparasite that occurs naturally in non-forested communities in Central and South America. Parasitic plants accumulate high levels of a water-soluble orange pigment in roots that was once among the most important food dyes in the Andean region. We conclusively address the chemical identification of this pigment and provide molecular and cellular insights on its biosynthesis and possible function. Summary: The herbaceous hemiparasite Escobedia grandiflora (Orobanchaceae) is used in traditional medicine in the Andean region. Escobedia roots accumulate high levels of an orange pigment with a significant relevance as a cooking dye that exhibits antioxidant and cardioprotective properties. Here, we aimed to confirm the chemical identity of the pigment and investigate its biosynthesis and function in Escobedia roots. We combined metabolic and cytological analyses with de novo transcriptome assembly, gene expression studies, and phylogenetic analyses. The pigment was conclusively shown to be azafrin, an apocarotenoid likely derived from the cleavage of β-carotene. RNA-seq supported by multispecies comparative transcriptome analysis and qRT-PCR allowed to propose candidate genes for the production of azafrin in Escobedia roots. We also showed that azafrin is delivered to the root apoplast and that it accumulates in the area where the Escobedia haustorium contacts the host's root. Our data suggest that azafrin production might rely on a carotenoid cleavage dioxygenase (CCD) different from CCD7 and that this apocarotenoid might function in the parasitism process. Together, our work represents an unprecedented step forward in our understanding of the Escobedia parasitization system.