Belowground Defence Strategies Against Sedentary Nematodes

Abstract

Plant parasitic nematodes (PPN) represent a major threat to agriculture as they produce high economic losses. Among them, the sedentary endoparasites (root-knot nematodes, RKNs, and cyst nematodes) complete their life cycle inside the host roots where they induce a special feeding site for nutrient uptake, namely, giant cells for RKNs and syncytia for cyst nematodes. The root system represents the first physical barrier for nematode penetration. Cell wall hardening strategies used against many pathogens are not very effective against them, as they use a robust stylet during penetration or migration to apply mechanical force and/or to secrete a mixture of cell wall degrading enzymes from the subventral esophageal glands. Plant defences against endoparasitic nematodes include mechanisms as pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), the last one leading to the hypersensitive response. The development of sensitive “omics” techniques, sometimes combined with feeding cell isolation, allowed global analysis of gene expression during this interaction. Hence, transcriptional changes associated to compatible and incompatible interactions of different plant species such as Arabidopsis, soybean, tomato, Medicago, etc. with different species of either cyst or RKN nematodes brought up a vast amount of genes induced or repressed during both interactions. Some of them will be useful for future applications on nematode control, as functional studies indicated their role in nematode resistance. Information on the molecular effectors used by nematodes during the cross talk with susceptible or resistant plants leading to plant defence responses is continuously increasing. Furthermore, in the recent years, some effectors that suppress plant defences were described, increasing the complexity of this particular plant-pathogen interaction.