Abstract
Sedentary endoparasitic nematodes are obligate biotrophs that modify host root tissues, using a suite of effector proteins to create and maintain a feeding site that is their sole source of nutrition. Using assumptions about the characteristics of genes involved in plant-nematode biotrophic interactions to inform the identification strategy, we provide a description and characterisation of a novel group of hyper-variable extracellular effectors termed HYP, from the potato cyst nematode Globodera pallida. HYP effectors comprise a large gene family, with a modular structure, and have unparalleled diversity between individuals of the same population: no two nematodes tested had the same genetic complement of HYP effectors. Individuals vary in the number, size, and type of effector subfamilies. HYP effectors are expressed throughout the biotrophic stages in large secretory cells associated with the amphids of parasitic stage nematodes as confirmed by in situ hybridisation. The encoded proteins are secreted into the host roots where they are detectable by immunochemistry in the apoplasm, between the anterior end of the nematode and the feeding site. We have identified HYP effectors in three genera of plant parasitic nematodes capable of infecting a broad range of mono- and dicotyledon crop species. In planta RNAi targeted to all members of the effector family causes a reduction in successful parasitism.
Highlights
Plant parasitism by nematodes is a major threat to global food security, with at least one nematode species targeting each of the world’s most economically important crops [1]
The nematode secretes a suite of proteins, termed ‘effector proteins’ that are responsible for initiating and maintaining the feeding site
We describe a diverse and variable effector gene family (HYP), the products of which are secreted into the plant by the nematode and are required for successful infection
Summary
Plant parasitism by nematodes is a major threat to global food security, with at least one nematode species targeting each of the world’s most economically important crops [1]. The most complex, well-adapted, economically important, and most widely studied are the sedentary endoparasites, including the root-knot and cyst nematodes of Clade 12 of the phylum Nematoda [3]. These biotrophic pathogens invade the host roots as second stage juveniles (J2) and migrate to cells near the vascular cylinder. At the time of induction of the feeding site the nematode becomes sedentary, losing the ability to move. Like other biotrophic plant pathogens, have evolved the ability to suppress host defences (reviewed in [5,6])
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