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initiation (
Qi et al., 2011
). These regulatory proteins are thought to func-
tion in further regulating various functional genes under glucose stress con-
dition. SAUR-like auxin-responsive (At4g31320) and jasmonate-responsive
(At2g25980) protein genes were identified (
Table 2.2
), suggesting a link
between auxin, jasmonate and sugar-signaling pathways in mediating stress
responses. In addition, oxysterol-binding protein-like protein (At5g57240)
is related to secondary metabolism and involved in the steroid metabolic
processes. Actin depolymerizing factor (At1g01750) is reportedly one of the
target proteins in rice seedlings induced by drought stress (
Ali and Komatsu,
2006
). At present, the functions of most of these protein genes are not fully
understood. In addition, substantial amounts of LLA23-induced genes are
unknown/hypothetical/putative/expressed proteins, with unknown func-
tions (
Table 2.2
). In all, the two groups of LLA23-inducible genes correlate
with the proposed dual function of the lily ASR protein.
4.2.2. Promoter Analysis of LLA23-Inducible Genes
Sixteen LLA23-inducible genes encoding transcription factors and signaling
molecules (
Table 2.2
) and 25 genes induced by ASR, glucose and drought
treatments (
Fig. 2.5
) were selected for the promoter sequence analysis. Of
the 25 genes induced by the three treatments, three (At5g60100, At2g23030
and At2g28960) are transcription factors and signaling genes. Therefore, a
total number of 38 genes were examined.
Table 2.3
summarizes ABRE,
DRE/CBF, sugar-related, CE1, and hormone-responsive core sequences
observed in the 38 LLA23-inducible genes identified by the microarray
analysis. Among these, 15 genes (39%) contain DRE/CBF-related (G/A)
(T/C)CGAC motif in their promoters (
Shinozaki and Yamaguchi-Shi-
nozaki, 2007
;
Thomashow, 1999
;
Yamaguchi-Shinozaki and Shinozaki,
2005
), suggesting that these genes are regulated by the DREB1/CBF or
DREB2 transcription factors. A grape ASR (VvMSA) protein has report-
edly formed heterodimers with drought response element binding (DREB)
proteins (
Saumonneau et al., 2008
). Eleven genes (29%) contain CE1 ele-
ment (ACGTG) in their promoters, suggesting that these genes are regu-
lated by ASR because the tomato ASR1 was reportedly bound CE1 of
ABI4 promoter (
Shkolnik and Bar-Zvi, 2008
). Also, 25 genes (66%) contain
ABRE core element (ACGTG) in their promoters, suggesting that they are
ABA-inducible genes similar to
Asr
.
Cakir et al. (2003)
have demonstrated
a specific binding of VvMSA to SURE1 and sucrose box 3 elements in the
grape putative monosaccharide transporter promoter. With the exception
of five LLA23-inducible genes (At5g53210, At4g33260, At1g22990,
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