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COOH
E
R
T
K
V
Cytosol
D
L
L
S
F
F
P
A
P
Y
R
I
K
I
Q
V
H
W
M
L
Y
F
V
V
L
L
A
T
A
M
I
Q
F
A
E
L
F
G
V
S
C
L
I
P
ER membrane
I
C
I
Y
F
S
C
A
L
V
K
V
A
A
G
A
L
A
V
A
I
T
H
V
L
F
T
I
N
M
V
V
D
A
S
L
W
T
V
Y
Q Y
I
A
K
K
L
F
S
M H
S
V
L
Lumen
P
D
E
P
D
W
I
A
Q
C
D
M
M
E
S
C
NH2
Fig. 6.3
A proposed model for CmERS1 topology on the ER membrane. Based on membrane fractionation,
GFP imaging, protease protection assay, and glycosylation analysis, we propose that CmERS1 is predominantly
localized to the ER and spans the membrane three times with its N-terminus facing the luminal space and its
C-terminus lying on the cytosolic side (Ma et al., 2006a).
High levels of
PeERS2
mRNA were detected only in the arils of ripe purple fruit. Although
the expression of
PeERS2
mRNA was enhanced during ripening, a markedly high level
of
PeERS2
mRNA was detected only in the arils of ripened purple passion fruit, and no
ripening-regulated expression was apparent in seeds. Exposure of mature green fruit to
ethylene increased the levels of
PeERS2
mRNA, suggesting that PeERS2 might play a role
in repressing ethylene responses at later developmental stages after fruit ripening has been
completed (Mita et al., 2002).
Ethylene perception has also been described to be involved in apple fruitlet abscis-
sion and early development (Cin et al., 2005). The apple (
Malus domestica
)
MdETR1
and
MdERS1
gene expression patterns were tissue specific, with
MdETR1
transcripts being
abundant in the peduncle, abscission zone, and seed than in the cortex of early developing
fruits (nonabscising fruitlets), even though the expression always remained at a steady-state
level. The
MdERS1
transcripts increased throughout shedding in all tissues of abscising
fruitlets, indicating a possible role for this ethylene receptor in abscission. An increase
in ethylene evolution and/or sensitivity at the abscission zone level would regulate the
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