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Haustorium initiation in the obligate parasitic plant Phelipanche ramosa involves a host-exudated cytokinin signal
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Edité par CCSD ; Oxford University Press (OUP) -
International audience. The heterotrophic lifestyle of parasitic plants relies on the development of the haustorium, a specific infectious organrequired for attachment to host roots. While haustorium development is initiated upon chemodetection of host-derivedmolecules in hemiparasitic plants, the induction of haustorium formation remains largely unknown in holoparasiticspecies such as Phelipanche ramosa. This work demonstrates that the root exudates of the host plant Brassica napuscontain allelochemicals displaying haustorium-inducing activity on P. ramosa germinating seeds, which increasesthe parasite aggressiveness. A de novo assembled transcriptome and microarray approach with P. ramosa duringearly haustorium formation upon treatment with B. napus root exudates allowed the identification of differentiallyexpressed genes involved in hormone signaling. Bioassays using exogenous cytokinins and the specific cytokininreceptor inhibitor PI-55 showed that cytokinins induced haustorium formation and increased parasite aggressiveness.Root exudates triggered the expression of cytokinin-responsive genes during early haustorium developmentin germinated seeds, and bio-guided UPLC-ESI(+)-/MS/MS analysis showed that these exudates contain a cytokininwith dihydrozeatin characteristics. These results suggest that cytokinins constitutively exudated from host roots playa major role in haustorium formation and aggressiveness in P. ramosa.
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