Characterisation of cell walls at the feeding site of Meloidogyne incognita

Meloidogyne incognita induces a unique feeding structure, termed giant cells, by
reprogramming plant cells in the feeding site within host plant roots. The nematode
modifies the function of cells including giant cell wall composition. Characterisation
of pectin, hemicellulose and glycoproteins of giant cell walls formed in different hosts
was analysed. In addition the role of cell-wall genes in nematode feeding site
development was also analysed.
In situ analysis was performed to determine the presence and distribution of giant cell
wall components; cell wall elements were quantified using enzyme linked
immunosorbent assay in nematode feeding sites on different host plants Arabidopsis
thaliana (Brassicaceae), Vigna angularis (Fabaceae) and Zea mays (Poaceae). The
cell wall compositions in the M. incognita feeding site were observed by comparison
with uninfected root tissues. There were distinct responses in terms of detection of
cell wall polysaccharides in the nematode feeding site of the different hosts.
Modifications of cell wall polysaccharides in giant cells formed in Arabidopsis were
minor compared to uninfected sections. By contrast, analysis of the giant cell wall
formed in Vigna angularis revealed decreased amounts of mannan, xylan, galactan,
processed arabinan, arabinogalactan protein and extensin. In Zea mays, xyloglucan,
methyl esterified pectic homogalacturonan, galactan, arabinogalactan proteins
increased in abundance in giant cell walls.
Arabidopsis plants that carried mutations in cell-wall related genes were analysed.
Mutants for genes important in the formation of hemicellulose (GLZ1, MSR1 and
MUR3) together with those of the pectin related genes BGAL5 and RGXT1 all resulted
in smaller gall development together with a concomitant reduction in nematode size
in addition to a reduction in the number of nematodes recovered. Converselymutation
of the pectin-related genes ARAD1 and ARAD2 or the glycoprotein-related genes led
to increased susceptibility to the nematodes.