Root-knot Nematodes and giant cells
Jones, M.G.K. and Goto, D.B. (2011) Root-knot Nematodes and giant cells. In: Jones, J., Gheysen, G. and Fenoll, C., (eds.) Genomics and Molecular Genetics of Plant-Nematode Interactions. Springer Netherlands, pp. 83-100.
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Of all the economically important plant parasitic nematodes, root-knot nematodes (Meloidogyne species) are amongst the most widespread, the best recognized and most widely studied. This is partly because infected roots develop galls where the nematodes feed, which with severe infection give roots a ‘knotted’ appearance. They have a remarkably wide host range, and are ubiquitous especially in tropical and sub-tropical regions of the world. Juveniles move through the soil rhizosphere and locate host roots, in which they migrate intercellularly to pro-vascular cells to form a feeding site. Here, in response to nematode secretions, they re-program the development of about 6 cells into ‘giant cells’, which provide them with the nourishment needed for them to complete their life cycle of about 4–5 weeks. Giant cells form by repeated mitosis without cytokinesis, and so become multi-nucleate. Wall ingrowths typical of transfer cells develop both where giant cell walls contact vascular elements and between neighbouring giant cells. These amplify the surface area of the cell membrane and enable solutes and water to enter the cells, and to move between giant cells in response to nematode feeding. The developing giant cells become filled with cytoplasm, prominent amoeboid nuclei, mitochondria and small vacuoles, and appear to be very active metabolically. Giant cell development is accompanied with a host of changes in gene expression, cytoskeleton changes, plant hormone changes and structural changes. The delicate interaction between the nematode and its associated giant cells is mediated via feeding tubes, derived from nematode gland secretions, which act as an ultrafilter and pressure regulator. As the infective worm-like J2 larvae develop via 3 moults to reach the adult stage, they swell and adult females become spherical, and lays eggs into a gelatinous matrix. Most root-knot nematodes reproduce by mitotic parthenogenesis, although facultative meiotic parthenogenesis also occurs (e.g. in M. hapla). The availability of new molecular technologies that enable detailed study of gene expression and regulation in giant cells, and new genomic technologies applied both to host and nematode pathogen, is leading to rapid advances in understanding host-pathogen interactions of this important plant pest species.
|Publication Type:||Book Chapter|
|Murdoch Affiliation:||Western Australian State Agricultural Biotechnology Centre|
|Copyright:||2011 Springer Science + Business Media B. V.|
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