"Frontmatter". In: Plant Genomics and Proteomics

S
PECIFIC
P
ROMOTER
S
EQUENCES
A
RE
R
EQUIRED FOR
R
EGULATED
G
ENE
E
XPRESSION
There are numerous types of promoters that can regulate gene expression.
These promoters can be constitutive or inducible. A constitutive promoter is
one that functions in all tissues under all conditions, whereas an inducible
promoter is only activated in response to specific stimuli. A constitutive pro-
moter may still drive differential levels of expression but should not be com-
pletely silent in any tissue. Table 5.1 lists a series of plant promoters and the
expression patterns that are observed when they are used in transformation
experiments (Lessard et al., 2002). The identification of such specific pro-
moters is of use in controlling the expression of a transgene when it is nec-
essary or desirable to target the expression of that transgene to specific
organs, tissues, or developmental stages. In addition to using plant-specific
promoters for this task, a number of chemically induced promoters have
been developed to enable a controlled activation of constructs.
T
HE
E
FFECT OF
E
NHANCER
E
LEMENTS ON
G
ENE
E
XPRESSION
An enhancer is a DNA sequence that greatly increases the expression of a
gene in its vicinity. The sequence can reside upstream or downstream, its 
T
H E
E
F F E C T O F
E
N H A N C E R
E
L E M E N T S O N
G
E N E
E
X P R E S S I O N
9 1

---

9 2
5. C
O N T R O L O F
G
E N E
E
X P R E S S I O N
T
ABLE 5.1. E
XAMPLES
OF
D
IFFERENT
T
YPES
OF
P
LANT
P
ROMO
TERS
U
SED
FOR
C
ONSTRUCTION
OF
T
RANSGENES
T
ype of pr
omoter
Name
Comments
Refer
ence
Constitutive
Ubiquitin
Plant-origin pr
omoter that drives
Plesse et al., 2001
high-level constitutive expr
ession,
but expr
ession level during
development may vary
Constitutive
tCUP
Cryptic pr
omoter fr
om tobacco
W
u et al., 2003
T
issue-specific
b
-Conglycinin
A
well-characterized pr
omoter 
Chen et al., 1986
embryo pr
omoter
that dir
ects embryo-specific
expr
ession 
T
issue-specific
Opaque-2
These pr
omoters show developmental
Rossi et al., 1997
endosperm 
regulation and expr
ession
pr
omoter
T
issue-specific
2A1
1
2A1
1 is a fr
uit-specific pr
omoter 
V
an Haar
en and Houck, 1993
fr
uit
derived fr
om tomato
T
issue-specific
Lhcb3 pr
omoter
Lhcb3 pr
omoter is a light-r
egulated 
Ali and T
aylor
, 2001
leaf
leaf-specific pr
omoter fr
om
Arabidopsis
T
issue-specific
Stgan
Exclusive expr
ession in stolons
T
rindade et al., 2003
stolon
Pollen specific
lat52 pr
omoter
Developmentally r
egulated but
Bate and T
well, 1998
drives high expr
ession during
pollen maturation
Reprinted fr
om 
Metab. Eng
. 
4, Lessar
d et al. Manipulating gene expr
ession for the metabolic engineering of plants, 67–79, Copyright 2002, with
permission fr
om Elsevier
.

---

orientation is not fixed, and enhancers can still function when placed at some
distance from the transcription start site. These elements do not control
whether or not the promoter is active, but they do affect the level of expres-
sion. Their effects can be magnified if they are present in multiple copies.
They can also have a greater enhancement when present in various combi-
nations. For example, analysis of the tCUP promoter (Wu et al., 2003) demon-
strated that when the long AT-rich region (between positions –350 and 
–161 bp relative to the transcription start site) was deleted a significant
decrease in promoter activity was observed, whereas oligomerization of 
this region enhanced activity. A 21-bp sequence (TAGCCCCAA
TTTCAAATTCAA) was also identified in a similar fashion and defined a
novel cryptic constitutive enhancer element the activity of which was depen-
dent on the AT-rich element itself.
As well as enhancing gene expression, some cis-acting regions can also
silence the expression of adjacent genes. A bidirectional mannopine synthase
(MAS) promoter contains elements that both enhance and silence gene
expression (Guevara-Garcia et al., 1999; Figure 5.2). The bidirectional pro-
moter controls the expression of two genes that encode enzymes for the syn-
thesis of mannopine in plant tissues infected with Agrobacterium tumefaciens.
The use of different MAS promoter regions in transformation experiments
demonstrated that the regulatory properties of these divergent promoters
result from the presence of orientation-dependent negative and positive reg-
ulatory regions. In particular, some of these elements have the unusual prop-
erty of acting as enhancers in one orientation and as silencers in the other.
This is an example of the complexity of the control and response elements
over a short region adjacent to the gene.