Fig 1.
A model for molecular interactions between a parasitic plant and a potential host.
An obligate parasitic plant, such as Striga spp., is represented on the left side of the figure and a potential host root on the right. The upper box shows the parasitic plant developmental stages (A, B, C, and D) associated with the corresponding molecular exchanges that can occur during a compatible interaction. The lower box shows the host-invading stage in which parasitic plant molecules likely trigger immunity in the host (E), leading to an incompatible interaction and arrest of parasitism. A: The strigolactones (SLs) perception by SL receptors triggers the germination of some parasitic plants, such as Striga and Orobanche species. B: Oxidoreduction processes enable the production of haustorium-inducing factors (HIFs) from precursors of HIFs (pre-HIFs), in some cases. The perception of active HIFs by HIF receptors activates formation of the haustorium, a globular invading organ. C: The haustorial hairs and the haustorial growth enable the attachment of the parasitic plant to the host root. D: Further growth of the haustorium and probable secretion of unknown virulence factors (i.e., small compounds) and/or effector proteins participate in the instalment of the parasite inside the host root. A vascular connection is finally established with the host root for nutrients uptake. E: Parasitic plant-derived molecules, such as pathogen-associated molecular patterns (PAMPs) and effectors, may activate PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI) through their recognition by PAMP recognition receptors (PRRs) and by nucleotide-binding domain and leucine-rich repeat-containing (NLR) receptors, respectively.