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4.2. ASR-Inducible Genes in
35S::LLA23
Plants
A microarray analysis of an LLA23-overexpressing transgenic line was
conducted to gain a more comprehensive view of LLA23-regulated gene
expression. Homozygous
35S::LLA23E
, which has higher LLA23 expres-
sion levels, was selected for the analysis in parallel with wild-type
Arabi-
dopsis
(Col) plants. The genotype-specific signal intensity for each of the
22,810 genes on the arrays was determined and analyzed with a
t
-test for
significant differences (
P
< 0.05). Only the genes with high significance
(
P
< 0.05) and fold change greater than 2 were selected. Thus, 206 genes
with expression ratios greater than twofold induction of expression and 204
genes with expression ratios greater than twofold repression of expression
in the LLA23-overexpressing plants were identified (
Yang et al., 2008
). All
these responsive genes are proposed to be modulated by LLA23. The upreg-
ulated and downregulated genes (101/12) with two and halffold induction
or repression in LLA23-overexpressing plants are listed in
Table 2.2
.
4.2.1. Classification of LLA23-Inducible Genes
The 101 LLA23-inducible gene products can be classified into two groups.
The first group includes functional proteins or proteins that probably
function in stress tolerance, including detoxification enzymes, LEAs, cold-
regulated proteins, transporters, water channel proteins, and cell wall-related
and defense-related proteins (
Table 2.2
). Detoxification enzymes such as
peroxidase (At3g01190) and glutathione S-transferase (At1g49860) are
considered to be involved in the protection of cells from active oxygen
radicals. LEAs have been shown to be involved in protecting macromol-
ecules, such as enzymes and lipids (
Hanin et al., 2011
;
Huang et al., 2012
).
Peptide transporters, carrier and water channel proteins are involved in the
transport of ions, water and proteins through plasma membranes and tono-
plast to adjust the osmotic pressure. Cell wall-related enzymes and extensin-
like protein are involved in structural fortification and remodeling of cell
wall upon exposure to pathogens and abiotic stresses (
Merkouropoulos and
Shirsat, 2003
). Among defense-related proteins, nonspecific lipid-transfer
proteins may exhibit antimicrobial activity upon various stresses (
Sun et al.,
2008
). The gene encoding dioxygenase-like protein (At1g14120) is respon-
sive to pathogen and stress (
Umate, 2011
;
Xu et al., 2010
). In addition,
pinoresinol reductase (At4g13660) may be involved in the production of
polyphenolic substances (antioxidants) (
Nakatsubo et al., 2008
). Importantly,
several ASR-induced enzymes such as 3-deoxy-D-manno-octulosonic acid
transferase (At5g03770), 4-alpha-glucanotransferase (At5g64860), indole
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