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INTRODUCTION
Plant parasitic nematodes occur globally and have a severe economic impact on agriculture through the infestation of agronomically important crops. Current methods of control, such as nematicides or crop rotations are inadequate and can have adverse environmental or economic effects (Lilley et al. 2011). The most economically important species are the sedentary endoparasites of the genus Meloidogyne (root-knot nematodes) and the cyst nematodes Heterodera and Globodera. Sedentary endoparasitic nematodes induce the formation of specialised feeding sites in plant roots, which support the development and reproduction of nematodes throughout the life cycle (Davis et al. 2004). The syncytia induced by cyst nematodes and giant cells formed by root-knot nematodes have a shared function in nutrient supply, but differ in their structure and the mechanism of their establishment. Syncytia are initiated by second stage juvenile nematodes (J2) from a single procambial, pericycle, endodermal or cortical parenchyma cell and expand into or along the vascular cylinder through the dissolution of adjacent cell walls. This results in the formation of a single hypertrophied multinuclear cell complex, which can contain up to 200 cells and is in close contact with xylem and phloem elements (Sobczak and Golinowski, 2009). In contrast, J2 of Meloidogyne spp. select up to 12 parenchymal cells within the stele that are induced to undergo mitosis without concomitant cytokinesis to form large, multinucleate giant cells from which the nematode feeds in turn (Berg et al. 2009). The formation of syncytia and giant cells requires substantial re-programming of root cell development, which arises from extensive changes in host gene expression (Gheysen and Fenoll, 2002). This process is triggered by secretions from the nematode pharyngeal gland cells that are introduced into the initial feeding cells via the nematode stylet. The establishment and maintenance of feeding sites are fundamental to the survival of endoparasitic nematodes. This makes them an obvious target of interest for novel control strategies and much research in the field of plant nematology is directed towards understanding the basis for their induction and development. A number of molecular approaches have elucidated some of the processes occurring during feeding site development (Gheysen and Mitchum, 2009) and the nematode effector proteins that may play a role in this...