Unraveling the mechanism underlying the suppression and activation of R gene mediated resistance to potato cyst nematodes by highly similar effectors

Since the final withdrawal in 2008 of most of the pesticides to control the soil-borne potato cyst nematodes in Europe, farmers have relied on the cultivation of resistant potato cultivars. This strategy is seriously threatened by outbreaks of resistance-breaking potato cyst nematodes. Preliminary data shows that potato cyst nematodes secrete elicitors of R gene mediated resistance, but also suppressors that may allow them to overcome nematode resistance in potato. Remarkably, the suppressors and elicitors of resistance genes are members of the same SPRYSEC effector gene family and the difference between them can be as little as a single amino acid polymorphism. The SPRYSEC effectors show high similarity to Ran-binding proteins that are involved in RanGTP-regulated nuclear import in eukaryotic cells. Nuclear import is essential for the functioning of several plant immune receptors. The objective of this proposal is to investigate whether the SPRYSEC effectors of potato cyst nematodes disrupt the nuclear import of plant immune receptors to suppress R gene mediated resistance. The presence of suppressors of specific resistance genes in potato cyst nematodes implicates that the classical gene-for-gene model for virulence in pathogens and resistance in plants does not apply to nematode-plant interactions. Consequently, the potato breeders cannot use conventional effector-based approaches to select for durable nematode resistance genes in potato. Instead, breeding nematode resistance in potato will have to change from finding resistance genes that recognise specific effectors to finding resistances for which no suppressors are present in natural nematode populations in potato growing areas