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greater than threefold in the LLA23-overexpressing treatment or greater
than sixfold in the glucose and drought treatments, and less than twofold
in the other two induced treatments were classified as highly stress-induc-
ible genes. Thus, only one LLA23-, 65 glucose-, and 36 drought-inducible
genes induced highly in each stress treatment were identified (
Table 2.4
). As
shown in
Fig. 2.6
, real-time quantitative polymerase chain reaction (Q-PCR)
analysis of the hypothetical protein (At4g27510), unknown (At3g17990),
and early-responsive to dehydration 7 (ERD7, At2g17840) confirmed that
they are highly inducible LLA23-, glucose-, and drought-inducible genes,
respectively. The expression profiles obtained using Q-PCR analysis are con-
sistent with those obtained through microarray analysis. Among the genes
highly induced by 3% glucose, most are categorized as cell wall-related, stress-
and defense-related, involved in amino acid and protein metabolism, and as
functional proteins responsive to osmotic stress, such as detoxification LEA,
transporter, and water channel proteins. Among the genes highly induced
by drought stress, a lot of them are functional and stress-related proteins
(
Table 2.4
). In addition, we could find a close-to-constitutively expressed gene
(At1g11890), whose expression ratio is 1.00 in the glucose treatment, 0.99 in
the LLA23-overexpressing treatment, and 1.01 in the drought treatment. This
gene may be useful as an internal control in the microarray analysis.
4.4.3. LLA23-, Glucose-, and Drought-Repressive Genes
Analysis of stress-repressive genes is also important in understanding molec-
ular responses to abiotic stresses. As previously described, 204 genes were
identified as LLA23-repressive, 757 were identified as glucose-repressive,
and 709 genes were identified as drought-repressive. However, only the
genes with a more than two and halffold change in expression ratio in the
LLA23-overexpressing treatment or a more than sixfold change in expres-
sion ratio in the glucose and drought treatments were classified based on
their expression profiles (
Fig. 2.7
). A total of 12 LLA23-, 144 glucose stress-,
and 116 drought stress-downregulated genes were identified and classified
using microarray analysis (
Tables 2.2 and 2.5
).
Among these repressive genes, fewer were downregulated by LLA23.
Six genes encoding one heat shock protein 101(At1g74310), one mito-
chondrial dicarboxylate carrier (At4g24570), one 5-adenylylsulfate reduc-
tase (At4g04610), and three hypothetical/unknown proteins were repressed
only by LLA23 (
Table 2.2
). Of these repressive genes, 5-adenylylsulfate
reductase is photosynthesis-related. In addition, one gene encodes PRH26
protein (At4g21990) located in chloroplast was repressed by both LLA23 and
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