Strigolactones and sesquiterpene lactones induce Orobanche cumana germination via KAI2d receptors through distinct processes

Orobanche cumana is an obligate parasitic weed belonging to the Orobanchaceae family and represents the most important biotic constraint to sunflower seed production in all the regions where sunflower is cultivated, except in North and South America. O. cumana seeds compensate for their limited reserves by having strict requirements for germination, which involve the detection of specific allelochemicals exuded by sunflower roots, known as germination stimulants (GS). To date, these stimulants have been identified as strigolactones (SLs) and sesquiterpene lactones (SqTLs). In this study, we characterized nine KAI2d receptors of O. cumana with respect to their ability to perceive GS. We demonstrated that at least four OcuKAI2d proteins function as receptors for both canonical and non-canonical SLs. In addition, we showed that these paralogs interact with the sunflower-derived SqTL, (-)-DCL, through a mechanism distinct from their interaction with SLs: they form a covalent adduct on a histidine residue within the binding pocket, adjacent to the serine of the catalytic triad. Our findings expand current knowledge on GS perception in O. cumana and offer promising perspectives for the development of sustainable and effective strategies for controlling this parasitic weed.