Agriculture Reference
In-Depth Information
some members of the WRKY family are also involved in the regulation ABA sign-
aling and are potential candidate genes for improving stress resistance, although
different WRKYs may have different roles in the regulation of stress responses.
22.4.3 Other ABA-Related Transcription Factors
Dehydration-responsive element-binding (DREB) transcription factors specifi-
cally interact with the dehydration-responsive element/C-repeat (DRE/CRT)
cis
-
acting element and control the expression of many stress-inducible genes in plants
(Yamaguchi-Shinozaki and Shinozaki
1994
). Previous studies often presumed that
DREBs act in the regulation of ABA-independent pathways. However, several
studies have suggested that some DREBs may also function in an ABA-dependent
manner for regulating stress tolerance. For example,
OsDREB1F
was induced by
ABA, and over-expression of
OsDREB1F
in Arabidopsis resulted in the upregu-
lation of
RD29B
and
RAB18
, which are typical ABA-dependent stress-induced
genes, suggesting that activation of stress-responsive genes by OsDREB1F may be
achieved via both ABA-dependent and ABA-independent pathways (Wang et al.
2008
).
ARAG1
, another ABA-responsive
DREB
gene, plays a role in seed germina-
tion and drought tolerance of rice, and an
ARAG1
-knockdown line was hypersensi-
tive to ABA during seed germination and seedling growth (Zhao et al.
2010
).
NAC (NAM, ATAF, and CUC) is a plant-specific transcription factor family
with diverse roles in development and stress regulation (Nakashima et al.
2012
).
SNAC1
is an ABA and stress-responsive NAC gene conferring drought resistance
in rice (Hu et al.
2006
).
SNAC1
-over-expressing transgenic rice plants were hyper-
sensitive to ABA application during seedling growth, and the over-expression lines
exhibited 22-34 % higher seed setting in the field than the negative control under
severe drought stress conditions imposed at the reproductive stage (Hu et al.
2006
).
Over-expression of another rice stress-responsive NAC gene
SNAC2
resulted in sig-
nificantly increased sensitivity to ABA, and the transgenic rice showed enhanced
cold tolerance (Hu et al.
2008
). These results suggest that some NAC transcription
factors also function as important transcriptional activators in ABA-dependent gene
expression and may be useful in stress tolerance improvement in crops.
Ethylene response factors (ERFs) are plant transcriptional regulators mediating
the progression of plant development and stress response (Gutterson and Reuber
2004
). The tomato ERF protein TSRF1 is able to interact with a GCC box-like
sequence containing the core sequence of the ZmABI4-binding-CE1-like ele-
ment and regulates the ABA response, and over-expression of
TSRF1
in tobacco
enhanced ABA sensitivity during germination, cotyledon expansion, and root elon-
gation (Zhang et al.
2008a
). In addition, over-expression of
TSRF1
in rice led to
improved drought and osmotic tolerance (Quan et al.
2010
). Another tomato ERF
transcription activator, TERF1, was proposed to act as a linker between the eth-
ylene and osmotic signaling pathways, and over-expression of TERF1 in tobacco
enhanced drought tolerance and ABA sensitivity during seedling development
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