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In-Depth Information
the identification of transcriptional events occur-
ring within syncytial cells was obscured by the
mass of transcriptional activity occurring in the
whole root (Klink et al. 2007b).
To understand the effects of infection of
roots by RKN, Ibrahim et al. (2011a) used the
Affymetrix GeneChip to examine the expression
of soybean genes in galls formed in roots by RKN
12 days and 10 weeks after infection. Results
showed that genes encoding enzymes involved
in carbohydrate and cell wall metabolism, cell
cycle control, and plant defense were altered,
providing insights into the interaction between
RKN and soybean and the formation and main-
tenance of giant cells.
Cephalic framework
Stylet
Stylet musculature
Valve of dorsal
pharyngeal gland
Lumen of the pharynx
Valve plates of
the median bulb
Ampulla of dorsal
pharyngeal gland
Valve of subventral
pharyngeal gland
Opening of the
secretory-excretory
duct
Median bulb
Dorsal
pharyngeal gland
Subventral
pharyngeal gland
Body wall musculature
Intestine
Host-Nematode Interaction
Fig. 7.2. Schematic representation of the anterior of a
J2 cyst nematode showing the position of the pharyngeal
glands (adapted from Lilley et al. 2005).
Cyst nematode and RKN are sedentary endopar-
asites that become sedentary at specialized feed-
ing sites. Syncytium and giant cells are the
feeding sites formed by SCN and RKN, respec-
tively. A syncytium originates from the amal-
gamation of several hundred cells between the
initial syncytial cell and adjacent cells, which
is characterized by the breakdown of the cell
walls. By contrast, giant cells originate from
six cells that undergo repeated mitosis without
intermittent cytokinesis, which is characterized
by the induction of nuclear division. The giant
cells are embedded in the plant root and form
a gall or root-knot in the end (Gheysen and
Mitchum 2011). Although giant cells and syn-
cytia have different ontogeny, they have simi-
lar ultra-structurem such as dense cytoplasm and
enlarged nuclei. They also have similar func-
tions to support nematodes in finishing their life
cycles, from the infective J2-stage juvenile to the
J4 mature egg-laying female.
The nematode's effectors, which are gener-
ated in pharyngeal glands (Figure 7.2) (Lilley
et al. 2005) and injected into plant cells through
a protrusible hollow mouth spear called a stylet,
play important roles in the formation of feeding
sites (Gheysen and Mitchum 2011). The subven-
tral glands are thought to be important for the
early stages of parasitism because they produce
a variety of plant cell-modifying proteins that
facilitate nematode's migration through the plant
root (Hewezi et al. 2008; Qin et al. 2004). Dor-
sal glands are important for the development and
maintenance of feeding sites because the effec-
tors that induce the plant's response to infec-
tion are mainly secreted from the dorsal gland
(Bellafiore and Briggs 2010; Gheysen and
Mitchum 2011). The effector proteins and their
interactions with host proteins have been proved
to coordinate many of the events happening dur-
ing the formation of feeding cells, from early ini-
tiation of feeding cells to their complete develop-
ment into a transfer cell-like nutrient sink (Figure
7.3) (Gheysen and Mitchum 2011).
When the formation of SCN or RKN feed-
ing cells is initiated, extensive cell wall archi-
tectural modifications such as dissolution, disas-
sembly, and thickening take place. The activity
of cell wall biosynthetic and cell-wall-degrading
enzymes mediated these processes (Gheysen
and Mitchum 2011). But whether the
-1,4-
endoglucanase (EGases) of nematode or plant
β
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