Dehydrocostus lactone is exuded from sunflower roots and stimulates germination of the root parasite Orobanche cumana

Dehydrocostus lactone (DCL) is released in minute quantities from sunflower roots to the rhizosphere. This was discovered after identifying its role as germination stimulant for the tiny seeds of the root parasitic weed Orobanche cumana. We hypothesize that DCL represents a family of compounds that also interact with other organisms in soil. [Display omitted] ► Dehydrocostus lactone is exuded by sunflower roots. ► This guaianolide sesquiterpene lactone acts as interspecific chemical signal. ► Like strigolactones, it stimulates germination of root parasitic weeds. ► Its biosynthesis is inhibited by mevastatin and not by fluridone. ► Phosphate starvation reduces its production. The germination of the obligate root parasites of the Orobanchaceae depends on the perception of chemical stimuli from host roots. Several compounds, collectively termed strigolactones, stimulate the germination of the various Orobanche species, but do not significantly elicit germination of Orobanche cumana, a specific parasite of sunflower. Phosphate starvation markedly decreased the stimulatory activity of sunflower root exudates toward O. cumana, and fluridone – an inhibitor of the carotenoid biosynthesis pathway – did not inhibit the production of the germination stimulant in both shoots and roots of young sunflower plants, indicating that the stimulant is not a strigolactone. We identified the natural germination stimulant from sunflower root exudates by bioassay-driven purification. Its chemical structure was elucidated as the guaianolide sesquiterpene lactone dehydrocostus lactone (DCL). Low DCL concentrations effectively stimulate the germination of O. cumana seeds but not of Phelipanche aegyptiaca (syn. Orobanche aegyptiaca). DCL and other sesquiterpene lactones were found in various plant organs, but were previously not known to be exuded to the rhizosphere where they can interact with other organisms.