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about how the cyst nematode induces and main-
tains the syncytium (Alkharouf et al. 2006; Ithal
et al. 2007a; Khan et al. 2004).
Khan et al. (2004) conducted a cDNA
microarray with approximately 1,300 cDNA
inserts targeted to identify differentially
expressed genes during the compatible interac-
tion of SCN using 2-d infected soybean roots.
They found that the repetitive proline-rich glyco-
protein, the stress-induced gene
SAM22,
todes begin to select their feeding sites (Klink
et al. 2007a).
It was observed that when nematode infec-
tions happen, expressions of genes change not
only in the hosts but also in the nematodes (Ita-
hal et al. 2007a). To find whether there were
any correlations of gene expression between the
hosts and the nematodes, Ithal et al. (2007b)
analyzed the expression of gene transcripts in
soybean and SCN, at the same time using the
Affymetrix GeneChip soybean genome array.
They identified 429 soybean genes that were
significantly differentially expressed and were
involved in various pathways, such as primary
metabolism, stress and defense responses, cell
wall modification, cellular signaling, and tran-
scriptional regulation. Meanwhile, 1,850 signif-
icantly differentially expressed SCN genes were
also identified, then grouped into nine different
clusters (Ithal et al. 2007a). The study provided
new insights into soybean responses to nema-
tode infection compared with previous studies,
because gene expressions of the nematodes and
their host plants were studied at the same time.
Laser capture micro-dissection (LCM) is an
effective means to isolate homogeneous cell pop-
ulations with a high degree of precision and accu-
racy. Using this method, Klink et al. (2007b)
assayed gene transcript abundance in syncy-
tial cells in roots of cultivar Peking infected
by incompatible and compatible populations of
SCN. They observed that in syncytial cells from
incompatible roots at 3 dpi (days post infec-
tion), expressions of genes encoding lipoxy-
genase (LOX), heat shock protein (HSP) 70,
and superoxidase dismutase (SOD) were signifi-
cantly elevated. However, in those formed during
a compatible interaction, genes encoding pro-
hibitin, the epsilon chain of ATP synthase, allene
oxide cyclase, and annexin were more abundant.
The results indicated that gene expression was
different between syncytial cells from incompat-
ible and compatible roots. Moreover, they found
that genes that were differentially expressed in
syncytial cells were not differentially expressed
in the whole root analyses. Results suggested that
-1,3-
endoglucanase, peroxidase
, and those involved
in carbohydrate metabolism, plant defense and
signaling were upregulated two days after inoc-
ulation in inoculated roots, compared to the non-
inoculated ones.
In order to understand the dynamic changes
of gene expressions, Alkharouf et al. (2006) used
microarray to study the changes of gene expres-
sions within roots of susceptible soybean vari-
eties infected by SCN at 6, 12, and 24 hours
and 2, 4, 6, and 8 days post-inoculation (dpi).
The microarray contained 6,000 cDNA inserts.
The genes that were induced across most time
points or at a specific time point were iden-
tified. They included the
WRKY6
transcription
factor,
EIF4a
, and the stress-related gene
SAM-
2
2. Similar study was also conducted by Puthoff
et al. (2007), in which a new platform of soy-
bean Affymetrix GeneChip representing 35,593
soybean transcripts was adopted. A large pro-
portion of differentially expressed genes iden-
tified were associated with cell wall structure,
including
expansin
and
pectate lyase
. Others
were involved in several pathways, like disease
and defense, phytohormone metabolism, and
histones.
In order to compare gene expression dur-
ing both compatible and incompatible reac-
tions, Klink et al. (2007a) started a time-course
microarray analysis using the Peking soybean
variety infected by incompatible (I) and com-
patible (C) populations of SCN. A substan-
tial difference in gene expression was identified
between I and C at 12 hours post-infection, indi-
cating soybean can differentiate between I and
C nematode populations even before the nema-
β
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