Can the plant immune system be activated against animal parasites such as nematodes?

Plants have an immune system that can be exerted by every cell against a vast array of pathogens and parasites. This immune system has several levels of specialisation. A first level induces a general basal defence, after which specific pathogenassociated molecular patterns (PAMPs) are recognised by plant receptors. Normally, this basal defence is overcome by specialised pests by secreting specific effectors that suppress this first line of defence. Plant-parasitic nematodes have been found to secrete several such effectors through amphid and cuticle secretions or directly into the cells through their stylets. Many studies carried out on endoparasitic sedentary nematodes (ESN), in particular, reported the suppression of plant defence, especially in terms of down-regulation of the genes involved in salicylic acid (SA)-mediated defence, in the very first stages of plant-nematode interaction. However, plants can be immunised or primed against nematode attacks. Immunised plants respond to nematode infection more rapidly and efficiently and let a minor number of invasive juveniles become sedentary, develop to gravid females and reproduce. Immunisation of plants can be achieved by pre-treatments with chemicals that are functional analogues of the phytohormones that mediate defence reactions, such as salicylic acid (SA). Moreover, plants provided with the beneficial microorganisms commonly present in a healthy rhizosphere, such as arbuscular mycorrhizal fungi or opportunistic symbiotic fungi, have been found to be immunised against ESN. Immunisation is mainly mediated by up-regulation of SA-dependent defence genes, such as pathogenesis-related genes (PR-genes). Immunisation is systemic and can also work against herbivorous insects.