TABLE CONTENTS

SESSION TWENTY-FIVE – MOLECULAR INTERACTIONS IN
NEMATODE-BACTERIA ASSSOCIATIONS AND SYMBIOSIS
CONVENORS: KEITH DAVIES & AURELIO CIANCIO
Somaclonal Variation in Plant Parasitic Nematodes as Revealed by
Pasteuria: The Potential Importance of Innate Immunity
Davies, K.G.
Plant Pathology and Microbiology Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
Pasteuria penetrans is an endospore forming bacterial parasite of root-knot nematodes
(Meloidogyne spp.) that is host specific. Electron micrograph studies suggest that small fibrillike
structures on the surface of the nematode cuticle are involved in attachment. Endospores
can consistently attach to one population of nematode but not another and this represents a
first order interaction. To look at this in more detail, endospore attachment studies were
undertaken between clonal lines of juveniles of M. incognita and M. hapla, that reproduce by
obligate parthenogenesis and facultative meiotic parthenogenesis respectively. Results
revealed cuticle variability between second-stage juvenile broods of individual females
derived from a single individual in both sexual and asexual nematode species. This suggests
that second order mechanisms exist that produce functional differences in the cuticle surface
that affect Pasteuria adhesion.
The IGF1 signalling pathway in mammals is related to the DAF2 pathway in Caenorhabditis
elegans and influences, amongst other things, fecundity, longevity and the stress response.
The DAF2 pathway, involved in dauer formation, is also important in the worm’s innate
immune system. Changes to the cuticle surface of C. elegans srf mutants have been shown to
affect microbial adhesion and the worm’s innate immune system has been implicated.
Peptides inhibitory to IGF1 have been shown to alter C. elegans fecundity and longevity and
were tested to see if they had any effect on the attachment of Pasteuria endospores to secondstage
juvenile cuticle. Preliminary experiments suggest that the attachment of endospores to
second-stage juveniles of root-knot nematodes exposed to peptides significantly affected
attachment at 18 – 21 hours post-exposure. This result shows the potential importance of
innate immunity in generating functional variation to the cuticle surface that affects Pasteuria
adhesion.
5 th International Congress of Nematology, 2008 94