Evolution of pathogen effectors to carry out novel functions in planta

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The British Potato Council estimates the UK potato production, processing and retail markets to be worth around £3 billion per annum. The potato cyst nematodes Globodera rostochiensis and G. pallida, commonly known as eel worms, are important soil pests that cause major economic losses to potato growers. Globodera pallida is the most prevalent species in the UK and its control is the most problematic. A lack of commercially favoured resistant potato varieties and concerns surrounding the use of chemical control measures have resulted in G. pallida being an intractable problem to farmers both in the UK and in many other countries. G. pallida lives as a parasite and must complete the majority of its life-cycle in potato roots. It has a complex interaction with its plant host. Juvenile nematodes are microscopic worms that hatch from eggs in the soil upon detecting a host plant growing nearby, then locate and subsequently invade the roots of the host. The nematode migrates inside the root and selects a single root cell that it transforms into a large specialised feeding cell. Profound changes in plant cell structure and gene expression are induced by the nematode in establishing the feeding cell. These changes are mediated by proteins from the nematode, called 'effectors', directly injected into the host plant through a needle-like mouthpart.Surprisingly little is known about the majority of these effectors; most have no ascribed function and no similarity to other proteins. Furthermore, even those with similarity to proteins of known function appear to have diversified. Recently we have accumulated strong evidence that a group of proteins, similar to glutathione synthetase (GS), have evolved to carry out a new function, and are deployed as effectors by potato cyst nematodes. Given that these appear to be specific to this lineage of plant-parasitic nematodes, we aim to characterise their new function in the hope that they will lead to a new target, specific to these pests.In the first instance, we will determine how important these "GS-like effectors" are to the nematode, by utilising a highly targeted technique, known as RNA-interference. This will knock-down all these genes simultaneously and stop the proteins being delivered to the plant, allowing us to determine what large-scale effect these GS-like effectors have on the ability of the animal to parasitise the plant. Secondly, to gain insights into their function we will determine exactly which GS-like effectors are injected into the plant and where using a combination of antibody recognition and protein purification techniques. These data will allow us to focus on the most abundant GS-like effectors, and determine whether or not the expression of those genes in the plant alters the physiology of the plant and its ability to sustain a nematode infection, i.e. harbour more or less nematodes than control plants. Finally, we will use a range of techniques to elucidate the novel enzymatic process catalysed in plants by the G. pallida glutathione synthetase-like effectors so providing insight into their evolved role. The characterisation of a novel enzyme activity unique to plant parasitic nematodes, which is essential for their success as a parasite, may provide a foundation for the rational design of a chemical inhibitor that will afford control of these economically important parasites, without the off-target effects common to many pesticides.