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et al. 2001,
Reymond 2001, Kempema et al. 2007
). Analysis of
≈
7000
Arabidopsis
genes (which is 25-30% of this plant's genome) suggested that
≈
300 of the 7000
genes (4.3%) evaluated are involved in defense (
Maleck et al. 2000
). Comparison
of gene transcript profiles after plants were exposed to different stresses
revealed that some genes have overlapping roles in defense; thus, microarray
analyses can elucidate how plants respond to multiple stressors.
Microarrays of
Arabidopsis
expressed sequence tags (ESTs) have become avail-
able from several core laboratory sources since this species' genome was sequenced
(
Reymond 2001
). The microarrays allow simultaneous hybridization of probes to
an array of immobilized DNA fragments that correspond to a specific gene. After
scanning the microarray with a laser scanner, the signal for each fragment reflects
the abundance of the corresponding messenger RNA in the sample (
Maleck et al.
2000
). For example,
Kempema et al. (2007)
found that feeding by nymphs of
type B of the silverleaf whitefly,
Bemisia tabaci
, up-regulated 700 transcripts and
down-regulated 556. The responses were qualitatively and quantitatively different
from those induced by chewing insects or by aphids. Phloem-feeding insects such
as
Bemisia
feed for long periods but cause minimal tissue damage.
Many plants produce volatile organic compounds (VOCs) in response to feed-
ing damage caused by herbivores (
Dicke 1999
). These VOCs may influence neigh-
boring plants to respond rapidly to wounding, or to insect or plant pathogen
attack. Some VOCs attract predators and parasitoids to the insect herbivore and
DNA microarrays will allow researchers to analyze which genes are involved in
this type of plant defense. DNA microarrays allow researchers “to determine
the extent to which VOCs can elicit defense-related transcripts in neighboring
plants” (
Arimura et al. 2000a,b
).
It appears that a complex network of interdependent signaling pathways
convey molecular messages in
Arabidopsis
that identify the type of pest, which
allows the plant to mount an appropriate response (
Reymond 2001
). Integrating
the information on plant responses, obtaining an understanding of the com-
munications that take place between the different defense response pathways,
and obtaining a complete catalog of response genes should be achievable. Thus,
the global analysis of plant gene expression on microarrays and the complete
sequencing of the
Arabidopsis
and rice genomes could revolutionize the anal-
ysis of insect-plant interactions. Microarray research will bring together ecolo-
gists, molecular biologists, and plant scientists (
Maleck et al. 2000, Baldwin et al.
2001
). Some caution is needed, however, because conducting and analyzing
microarray experiments requires careful consideration of experimental design
and statistical analysis (
Kerr and Churchill 2001a,b, Quackenbush 2001
).
