Tissue specific expression and genomic organization of bitter sesquiterpene lactone biosynthesis in Cichorium intybus L. (Asteraceae)

Chicory (Cichorium intybus L.) produces bitter sesquiterpene lactones (STLs). Some enzymes in the biosynthetic pathway towards these compounds have been characterized. However, the genomic organization and tissue specificity of their biosynthesis is largely unknown. Concentrations of two sesquiterpene lactones and expression of genes involved in the first dedicated biosynthetic step were measured in different chicory tissues. BAC clones containing different genes encoding germacrene A synthase were sequenced, and revealed several tightly linked paralogs. Promoters of genes encoding two germacrene A synthases were fused to GFP and expressed in plants regenerated from transformed chicory hairy root cultures. Highest expression was observed in the epidermis of leaves and external root tissue. This work opens the possibility to select for chicory germplasm diversified in STL content, and to study their role in chicory in defence and physiology.