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under salt stress (100-150 mM NaCl), only 50% of
Arabidopsis
seeds germinate, but in the presence of SA (0.05-0.5 mM), seed
germination increases to 80%. Exogenous application of SA also
partially reverses the inhibitory effect of oxidative (0.5 mM para-
quat) and heat stress (50°C for 3 h) on seed germination (Alonso-
Ramirez et al., 2009). SA is also involved in the regulation of
the alternative oxidase (AOX) pathway in plants by inducing and
regulating its gene expression (Kapulnik et al., 1992). AOX is an
enzyme, which controls the adenosine triphosphate (ATP) syn-
thesis to maintain growth rate homeostasis. SA treatment induces
AOX1
gene expression levels that increases from two- to six-fold
after 4 h of induction (Norman et al., 2004). SA regulates the
many senescence-associated genes (SAGs) transcript. Transcripts
of several SAGs, such as
SAG12
, are considerably reduced or
undetectable in SA-deficient
Arabidopsis
plants (Morris et al.,
2000). Moreover, SA activates the expression of the
Arabidopsis
senescence-related genes α
VPE,
γ
VPE,
WRKY6,
WRKY53
and
SEN1 that encode two vacuolar-processing enzymes, two tran-
scription factors and a protease, respectively (Kinoshita et al.,
1999; Robatzek and Somssich, 2001; Miao et al., 2004; Schenk
et al., 2005).
13.3
Stress-regulated promoters and gene expression
the eukaryotic
promoter
architecture:
the controller
Eukaryotic DNA-dependent RNA polymerase II (RNA Pol II)
is responsible for the transcription of the genetic information
encoded in the DNA sequence protein-coding genes (Smale and
Kadonaga, 2003). The correct spatial and temporal transcrip-
tion of genes needs to be tightly controlled as it is the first step
in differential gene expression (Maston et al., 2006), which is a
prerequisite for the execution of biological processes such as cell
growth, morphology, the development of multi-cellular organ-
isms, the response to environmental conditions, disease and
differentiation in all eukaryotic organisms. Transcription regu-
lation of eukaryotic protein-coding genes (class II) is an orches-
trated process that requires the concerted functions of multiple
proteins or transcription factors (Martinez, 2002; Maston et al.,
2006). The region of the gene upstream of the coding and 5′
UTR regions is called the promoter and is also known as the
upstream region or the regulatory region of the gene (Figure
13.2). The eukaryotic promoter structure is responsible to a large
extent for the regulation of transcription.
The promoter is composed of a core promoter and proxi-
mal promoter elements. The distal elements may contact the
