TABLE CONTENTS

Root-knot Nematodes Manipulate Plant Cytoskeleton during a Compatible
Interaction
Favery, B., M.C. Caillaud, M. Quentin, P. Lecomte, J. De Almeda-Engler & P. Abad
UMR INRA 1301-UNSA-CNRS 6243 - Interactions Biotiques et Santé Végétale, Sophia Antipolis, France
Root-knot nematodes induce the redifferentiation of root cells into multinucleate and
hypertrophied giant cells essential for nematode growth and reproduction. The distribution of
microtubules and microfilaments in giant cells has recently attracted considerable attention.
To understand how nematodes are able to manipulate host functions to their own advantage,
we focused on the characterization of Arabidopsis genes early induced during giant cell
development. We characterized the first plant candidate gene implicated in giant cell actin
cytoskeleton reorganization (Favery et al., 2004). Three formin genes are induced in giant
cells. Formins are actin-nucleating proteins that stimulate the de novo polymerization of actin
filaments. We demonstrated that AtFH6 was anchored to the giant cell plasma membrane and
was uniformly distributed. Suppression of the budding defect of a yeast formin mutant
showed that AtFH6 regulates polarized growth by controlling the assembly of actin cables.
Our results suggest that formins may regulate giant cell isotropic growth by controlling the
assembly of actin cables. Actin cables would guide the vesicle trafficking needed for
extensive plasma membrane and cell wall biogenesis. In addition, we will present a complete
functional analysis in planta of a Microtubule-Associated Protein, MAP65-3. We showed that
MAP65-3 is essential for giant cell development during root-knot nematode infection and that
cytokinesis was initiated but not completed in giant cells (Caillaud et al., 2008). In developing
giant cells, MAP65-3 was associated with a novel kind of cell plate — the giant cell mini cell
plate — that separates daughter nuclei. In the absence of functional MAP65-3, giant cells
started to develop but failed to fully differentiate and were eventually destroyed. These
defects in giant cells impaired the maturation of nematode larvae. Subcellular localization of
MAP65-3 and microtubule organization analysis in the map65-3 mutant demonstrated that
MAP65-3 played a critical role in organizing the mitotic microtubule array both during early
and late mitosis.
Favery et al. (2004). Arabidopsis formin AtFH6 is a plasma membrane-associated protein upregulated in giant cells induced
by parasitic nematodes. Plant Cell 16, 2529-2540.
Caillaud et al. (2008). MAP65-3 microtubule-associated protein is essential for nematode-induced giant cell ontogenesis in
Arabidopsis. Plant Cell, www.plantcell.org/cgi/doi/10.1105/tpc.1107.057422.
5 th International Congress of Nematology, 2008 77