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Regulation of pheromone biosynthesis in the Z strain Э of the European corn borer Ostrinia nubilalis.

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Archives of Insect Biochemistry and Physiology 65:29–38 (2007)
Regulation of Pheromone Biosynthesis in the “Z
Strain” of the European Corn Borer, Ostrinia nubilalis
H.S. Eltahlawy, J.S. Buckner, and S.P. Foster*
The regulation of pheromone biosynthesis by the neuropeptide PBAN in the Z strain of the European corn borer, Ostrinia
nubilalis, was investigated using labeled intermediates. Injection of radiolabeled acetate showed PBAN did not influence the
de novo synthesis of saturated fatty acids in the gland. When deuterium-labeled myristic acid was topically applied to the
gland, females injected with PBAN produced more labeled pheromone than did control females, indicating that PBAN controls
one of the later steps of pheromone biosynthesis. Although more myristic acid was ∆11-desaturated in the gland in the
presence of PBAN, this was counterbalanced by less ∆11-desaturation of palmitic acid, indicating that desaturase activity did
not change overall. This change in flux of myristic acid through to pheromone was shown to be caused by increased reduction
of fatty acid pheromone precursors occurring in the presence of PBAN. Arch. Insect Biochem. Physiol. 65:29–38, 2007.
© 2007 Wiley-Liss, Inc.
KEYWORDS: pheromone biosynthesis-activating neuropeptide; PBAN; Lepidoptera; Pyralidae; fatty acid reduction
INTRODUCTION
In most species of moths, the female produces
and releases a volatile sex pheromone that attracts
conspecific males. To date, the sex pheromones or
attractants (i.e., Witzgall et al., 2004) of roughly
1,600 species of moths have been identified, with
the chemicals sorting into two major types of compounds: those with structural similarity to common fatty acids and those with a hydrocarbon
structure (Witzgall et al., 2004). The fatty acid–like
compounds appear to be more common, being
used by 42 out of the 50 families of Lepidoptera
for which pheromones or attractants have been
identified (Witzgall et al., 2004).
The fatty acid–like compounds typically have
an even number of carbon atoms (8–18) in a
straight chain, with one or more double bonds and
terminal oxygenated functionality of an alcohol,
acetate ester, or aldehyde (Tillman et al., 1999).
These compounds are biosynthesized in a specialized gland, located between the 8th and 9th abdominal segments of the female. Their biosynthesis
involves de novo synthesis of medium-chain
Department of Entomology, North Dakota State University, Fargo, North Dakota
Contract grant sponsor: USDA-NRI; Contract grant sponsor: NSF; Contract grant number: EPS-0132289.
Abbreviations used: ACCase = acetyl CoA carboxylase; D3-14:COOH = [14,14,14-D3]-tetradecanoic acid; D4-16:COOH = [7,7,8,8-D4]-hexadecanoic acid;
D5-Z11-14:COOH = [13,13,14,14,14,14-D5]-(Z)-11-tetradecenoic acid; E11-14-OAc = (E)-11-tetradecenyl acetate; E11-14:Acyl = (E)-11-tetradecenoate;
FAME = fatty acid methyl ester; GC-MS = gas chromatography-mass spectrometry; HPTLC = high performance thin layer chromatography; PBAN =
pheromone biosynthesis-activating neuropeptide; TGs = triacylglycerols; TLC = thin layer chromatography; Z11-14:OAc = (Z)-11-tetradecenyl acetate; Z1114:Acyl = (Z)-11-tetradecenoate;; Z11-16:Acyl = (Z)-11-hexadecenoate; 14:Acyl = tetradecanoate; 14:Me = methyl tetradecanoate; 15:Me = methyl
pentadecanoate; 16:Acyl = hexadecanoate; 16:Me = methyl hexadecanoate.
*Correspondence to: Dr. S.P. Foster, Department of Entomology, North Dakota State University, P.O. Box 5346, Fargo, ND 58105-5346.
E-mail: Stephen.Foster@ndsu.edu
Received 25 July 2006; Accepted 20 January 2007
© 2007 Wiley-Liss, Inc.
DOI: 10.1002/arch.20175
Published online in Wiley InterScience (www.interscience.wiley.com)
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Eltahlawy et al.
length, saturated fatty acids, usually stearic or palmitic, which are partially metabolized to produce the
pheromone components. Specific steps in this metabolism include desaturation, cytosolic β-oxidation (2-carbon chain-shortening), reduction (to an
alcohol), and acetylation (to produce acetate esters)
or oxidation (to produce aldehydes) (reviewed in
Bjostad et al., 1987, Tillman et al., 1999, Jurenka,
2003).
In many species of moths, biosynthesis of such
pheromone chemicals is under the regulation of
PBAN (Raina, 1995, Rafaeli and Jurenka, 2003).
PBAN was first isolated and sequenced from
Helicoverpa zea (Raina et al., 1989). Since this first
identification, other PBANs have been sequenced
from a number of other moths (for a review, see
Rafaeli and Jurenka, 2003). All PBANs have a high
degree of similarity at the C-terminus, in which
an amidated terminal FXPRL (X = S, T, G, or V)
motif appears to confer activity (Rafaeli and
Jurenka, 2003). PBAN is produced in the brainsubesophageal ganglion complex and is released
into the hemolymph, probably from the corpora
cardiaca (Rafaeli and Jurenka, 2003). It is then
transported to the pheromone gland, where it interacts with a G protein–coupled receptor (Choi
et al., 2003).
PBAN is thought to regulate pheromone biosynthesis in moths by controlling the activity of a
single pheromone biosynthetic enzyme. To date,
only a handful of studies have investigated which
enzyme is controlled by PBAN. Somewhat surprisingly, given the similarity of moth pheromone biosynthetic systems and the consistency of PBAN in
regulating pheromone biosynthesis (Rafaeli and
Jurenka, 2003), different studies have indicated that
PBAN may control different enzymes, according to
the species. In several species (Tang et al., 1989;
Jacquin et al., 1994; Jurenka et al., 1991a; Zhao et
al., 2002), PBAN influences a step in fatty acid synthesis, probably the conversion of acetyl-CoA to
malonyl-CoA by the enzyme acetyl CoA carboxylase. In other species, it influences the metabolism
of fatty acids including their reduction (Martinez
et al., 1990, Fabrias et al., 1995, Ozawa and
Matsumoto, 1996) or acetylation following reduc-
tion (Mas et al., 2000). One other study (Fang et
al., 1996) suggested that PBAN may control the mobilization of pheromone precursor fatty acids from
TGs. Together, these data indicate that either PBAN
is capable of controlling different biosynthetic enzymes in different species, perhaps by a common
mechanism (e.g., phosphorylation/dephosphorylation), or that the effect of PBAN on pheromone biosynthesis for a given species is more complex than
thought, and has yet to be elucidated fully.
The European corn borer, Ostrinia nubilalis
Hübner (Pyralidae), was introduced from Italy
into North America in the early 1900s, and has
become a major pest of corn in the United States
(Becker, 2000). In the 1970s, two distinct pheromone strains of O. nubilalis were identified, a socalled “Z-strain” using a mixture of Z11-14-OAc
and E11-14-OAc in a ratio of roughly 97:3, and
an “E-strain,” which uses the opposite ratio of isomers (3:97) (Klun, 1975, Cardé et al., 1978). In
both strains, the two pheromone components are
biosynthesized from myristic acid by the same
∆11-desaturase (Roelofs et al., 2002), which produces a roughly equal amount of the two precursor acids, Z11-14:Acyl and E11-14:Acyl (Wolf and
Roelofs, 1987). The distinct pheromonal blends
produced by the females of the two strains are
determined by differences in the specificity of
their respective fatty acid reductase, which, in the
Z-strain, shows greater selectivity for Z11-14:Acyl
and, in the E strain, for E11-14: Acyl (Zhu et al.,
1996).
Pheromone biosynthesis in both strains of O.
nubilalis is under the regulation of PBAN (Ma and
Roelofs, 1995). However, which enzyme(s) is controlled by PBAN has not been investigated in either strain. In this article, we report the results of
our study on the effect of PBAN on pheromone
biosynthesis in the “Z-strain” of O. nubilalis.
MATERIALS AND METHODS
Insects
“Z-strain” O. nubilalis were obtained as pupae
from Mass Rearing Laboratories (Madrid, IA). The
two sexes were separated from each other as puArchives of Insect Biochemistry and Physiology
May 2007
doi: 10.1002/arch.
PBAN Regulation in O. nubilalis
pae, and the female pupae maintained at 25 ±
0.5°C under a 16:8 (light: dark) photoperiod.
Adults were collected daily, just before the start of
the scotophase, and placed in 500-ml plastic containers, along with a 10% sugar solution absorbed
on cotton wool, under the same temperature and
photoperiodic conditions as the pupae. For the experiments, females, 1–2 days after collection, were
decapitated and left for 24 h before use (i.e., when
2–3 days old). This age corresponds to the time in
intact females when pheromone production is
maximal (Foster, 2004b).
Chemicals
The sodium salt of [2-14 C] acetic acid (51 mCi/
mmol) and BetaMax (liquid scintillation cocktails)
were purchased from MP Biomedicals (Aurora,
OH). Deuterium-labeled D3-14:COOH and D416:COOH were purchased from Cambridge Isotope Laboratories, Inc. (Andover, MA) and were
both greater than 99% isotopically pure. [13,13,14,
14,14,14-D 5]-Z11-14:OAc was a gift from Dr.
Christer Lofstedt (Lund University, Sweden). It was
converted to the corresponding acid, D5-Z1114:COOH, by hydrolysis with methanolic KOH
(O.5 M), followed by oxidation by pyridinium
dichromate in dimethyl formamide (Corey and
Schmidt, 1979). The acid was purified through a
small silica gel column constructed from a Pasteur
pipette. GC-MS analysis indicated that it was free
of any corresponding acetate or alcohol and was
>97% isotopically pure.
Synthetic Helicoverpa zea PBAN was purchased
from Bachem, Inc. (Torrance, CA), and tripentadecanoin and other chemical standards were from
Sigma Chemical Co. (St Louis, MO).
De Novo Synthesis of Fatty Acids
Radiolabeled 2-14C acetate was dissolved in
Manduca saline (4 mM NaCl, 40 mM KCl, 243 mM
sucrose, 18 mM MgCl, 3 mM CaCl, 0.1 mM
polyvinylpyrollidone, 1.5 mM PIPES, pH 6.5), and
2.5 µl (0.3µci) injected into the abdomen of a decapitated female, along with either saline or 5 pmol
Archives of Insect Biochemistry and Physiology May 2007
doi: 10.1002/arch.
31
PBAN in saline. Females were left for 2 h in the
dark at their rearing temperature before the pheromone gland was dissected. Ten glands were pooled
for either treatment and extracted with chloroform/
methanol (2/1 vol./vol.) for 24 h at –15°C. Following extraction, the gland extract was transferred
into a 1 ml Reacti-vial and the solvent removed
with a gentle stream of N2. The residue was then
base methanolyzed (Litchfield, 1972) by adding
100 µl of 0.5M methanolic KOH and allowing it
to react for 3–4 h at room temperature with occasional mixing. FAME were formed by adding 100
µl 1.0 M HCL (aq), and extracted with chloroform.
Aliquots (5% of total) of the extracts were transferred into separate 7-ml glass vials, the chloroform evaporated, and 6.5 ml of BetaMax added.
Radioactivity in each vial was counted using a
Packard model 2300TR liquid scintillation analyzer
(Packard Instrument, Co., Meriden, CT) at counting efficiency of 97% for 14C. A further aliquot (5%
of total) of the extract was subjected to normal
phase TLC, using silica HPTLC plates (EM Science,
Gibbstown, NJ) developed with hexane/ethyl ether/
formic acid (80:20:1). Radioactivity on the developed plates was counted using a Bioscan System
200 radio-TLC scanner (Bioscan Inc., Washington,
DC). Following counting, spots of samples and
various synthetic standards were visualized with
iodine vapor.
Topical Application of Fatty Acids
The pheromone gland of a female was extruded
by placing an alligator clip near the posterior end
of the abdomen, and a deuterium-labeled acid (in
DMSO) applied topically to the gland. Ten minutes after application, the clip was removed and
2.5 µl of either saline (NaCl, 188 mM, KCL, 4.8
mM, CaCl2, 2.6 mM, Hepes, 10.0 mM, glucose, 13.9
mM, pH 6.8) or PBAN (5 pmol in saline) injected
into the abdomen of the female. Insects were left
at ambient temperature for the assigned time, after which their pheromone gland was dissected and
extracted in either n-heptane (for pheromone analyses) or 1:2 dichloromethane:methanol (for glycerolipid analyses) for at least 16 h at –15°C. Either 25
32
Eltahlawy et al.
ng (E)-4-tetradecenyl acetate or 200 ng tripentadecanoin was added as an internal standard to the
respective solvents. The following experiments were
performed:
1. Effect on production of pheromone and
pheromone precursor acid. D3-14:COOH
(10 µg/µl in DMSO) was applied to the
gland and the amount of label in both pheromone components and precursor acids determined 2 h following application
2. Effect on fatty acid chain-shortening. D416:COOH (10 µg/µl in DMSO) was applied
to the gland and the amount of label in
14:Acyl determined 2 h following application.
3. Effect on fatty acid desaturation. The products of ∆11-desaturation in the pheromone
gland of female O. nublialis are Z11-14:Acyl
and E11-14:Acyl. However, since these moieties are readily reduced to pheromone (Zhu
et al., 1996), their quantities do not represent the total amount of ∆11-desaturation.
The ∆11-desaturase of O. nubilalis is also capable of desaturating 16:Acyl to Z11-16:Acyl,
which is not reduced but stored in the gland
(Roelofs et al., 2002, Foster, 2004b). Therefore, we tested the effect of PBAN on ∆11desaturation by analyzing for labeled Z1116:Acyl 2 h following application of D416:COOH (10 µg/µl in DMSO).
4. Effect on fatty acid reduction. D5-Z11-14:
COOH (5 µg/µl in DMSO) was applied to
the gland and the amount of label in Z1114:OAc and Z11-14:Acyl determined at 3
times (0.25, 0.75, 1.5 h).
Pooled extracts of 10–12 pheromone glands
were analyzed by GC-MS using a Hewlett-Packard
5890 Series II gas chromatograph/5972 mass selective detector. The GC was operated with splitless injection and fitted with a 30 m × 0.25 mm
id ZB Wax column (Phenomenex Inc., Torrance,
CA). The column oven was programmed from 80–
220°C at 15°C min–1 after an initial delay of 1
min. Helium was the carrier gas at a linear flow
velocity of 30 cm sec–1. The MS was used in the
selected ion mode, monitoring the following m/
z: 194 (for tetradecenyl acetates; = M+-acetic acid),
197 (D3-labeled tetradecenyl acetates), 198 (D4labeled tetradecenyl acetates), and 199 (D5-labeled tetradecenyl acetates).
Pooled glycerolipid extracts of 6–10 dissected
pheromone glands were analyzed as FAME, generated by base methanolysis (Litchfield, 1972), as
previously described. GC-MS conditions were as for
the pheromone analyses except the following m/z
were monitored: 242 (M+ of 14:Me), 246 (M+ of D4labeled 14:Me), 240 (M+ of methyl tetradecenoates),
244 (M+ of D4-labeled methyl tetradecenoates), 245
(M+ of D5-labeled methyl tetradecenoates), 270 (M+
of 16:Me ), 274 (M+ of D4-labeled 16:Me), 268 (M+
of methyl hexadecenoates), 272 (M+ of D4-labeled
methyl hexadecenoates), and 256 (M+ of 15:Me).
Statistical Analyses
The experiment testing the de novo synthesis
of fatty acids was replicated five times. In all other
experiments, at least 6 replicates of each treatment
were conducted. PBAN and saline treatments in the
various experiments were compared by Wilcoxon
Rank Sum tests. Differences between treatments are
reported at P < 0.05.
RESULTS
De Novo Fatty Acid Synthesis
There was no significant difference in mean radioactivity of the derivatized extracts between females injected with PBAN (mean = 1,083.4 ± 138
DPM) and those injected with saline (mean =
1,385 ± 106 DPM). Radio-TLC analysis showed
two major peaks at Rf = 0.22 and Rf = 0.52, as
well as a smaller peak at the origin. In both the
PBAN and saline samples, these two peaks accounted for roughly 65% of the total radioactivity (the peak at the origin accounted for roughly
6% of the total). No peak at an Rf value (=0.13)
corresponding to that of synthetic (Z)-11-tetradecenol (which would have resulted from hydrolysis of the major pheromone component) was
discernible in samples from both the PBAN- and
saline-injected females.
Archives of Insect Biochemistry and Physiology
May 2007
doi: 10.1002/arch.
PBAN Regulation in O. nubilalis
Pheromone and Fatty Acid Pheromone Precursor
Production From Myristic Acid
Females injected with PBAN and with D314:COOH topically applied to their pheromone
gland had significantly greater titers of both native
(Fig. 1a) and labeled (Fig. 1b) Z11-14:OAc than
did the corresponding females injected with saline.
The titers of native E11-14:OAc were very low in
all the samples, and no significant difference in
the respective mean titers of this compound between PBAN- and saline-injected females was observed (data not shown). Labeled E11-14:OAc was
undetectable in all the samples.
FAME analyses of glands treated with D314:COOH showed no significant differences in titers of labeled or native (data not shown) 14:Acyl,
Z11-14:Acyl and E11-14:Acyl between PBAN- and
saline-injected females (Fig. 2).
33
Fatty Acid Desaturation
Saline-injected females (mean = 0.095 ± 0.009
ng/female) had a significantly higher mean titer
of labeled Z11-16:Acyl than did PBAN-injected ones
(mean = 0.062 ± 0.009 ng/female).
Fatty Acid Reduction
Maximum titer of labeled Z11-14:OAc was
reached at the shortest time (0.25 h) analyzed following application of D5-Z11-14:OAc, for both
PBAN- and saline-injected females (Fig. 3a); there
was no significant difference between the respective titers of the two types of females at this time.
For the PBAN-injected females, labeled Z11-14;OAc
titer remained at this higher level until 0.75 h after application, before declining significantly by 1.5
h. In contrast, in the saline-injected females, the
Fatty Acid Chain-Shortening
No difference in mean titer of labeled 14:Acyl
was observed between PBAN- (mean = 0.18 ± 0.04
ng/female) and saline-injected females (mean =
0.21 ± 0.04 ng/female).
Fig. 1. Mean titers (and SEM) of (a) labeled Z11-14:OAc
and (b) native Z11-14:OAc in the pheromone gland of
decapitated Z-strain Ostrinia nubilalis females, topically
applied with D3-14:COOH, and injected with either PBAN
or saline. Means were derived from 10 replicates, with 10–
12 glands per replicate. Different letters atop bars indicate means that are significantly different (P < 0.05).
Archives of Insect Biochemistry and Physiology May 2007
doi: 10.1002/arch.
Fig. 2. Mean titers (and SEM) of labeled 14:Acyl, Z1114:Acyl, and E11-14:Acyl in the pheromone gland of decapitated Z-strain Ostrinia nubilalis females, topically
applied with D3-14:COOH, and injected with either PBAN
or saline. Means were derived from 10 replicates, with 8–
10 glands per replicate. Different letters (with the same
subscript) atop bars indicate means that are significantly
different (P < 0.05).
34
Eltahlawy et al.
Fig. 3. Mean titers (and SEM) of (a) labeled Z11-14:OAc and (b) native Z11-14:
OAc in the pheromone gland of decapitated Z-strain Ostrinia nubilalis females,
topically applied with D5-Z11-14:COOH,
and injected with either PBAN or saline.
Means were derived from 10 replicates,
with 10–12 glands per replicate. Different letters atop bars indicate means that
are significantly different (P < 0.05).
titer of labeled Z11-14:OAc titer had significantly
declined between 0.25 and 0.75 h. At the latter
time, there was a significant difference in the titer
of labeled Z11-14:OAc between PBAN- and salineinjected females. Native Z11-14:OAc titers were
similar at all three times for saline-injected females.
However, for PBAN-injected females native Z1114:OAc titers increased significantly from 0.25 to
0.75 h and remained at this higher level at 1.5 h.
At the two longer times, titers of native Z11-14:OAc
were significantly greater in PBAN-injected females
than in controls.
There were no differences in labeled (Fig. 4a)
or native (Fig. 4b) Z11-14:Acyl titers, in females
over time, or between females injected with PBAN
or saline at any given time.
DISCUSSION
The neuropeptide PBAN regulates the biosynthesis of sex pheromone in O. nubilalis (Ma and
Roelofs, 1995). Our data indicate that, in the “Zstrain” of O. nubilalis, PBAN affects biosynthesis
during the later steps, specifically following the production of myristic acid in the gland. Unlike several other species (Tang et al., 1989, Jurenka et al.,
1991b, Jurenka, 1997, Jacquin et al., 1994), PBAN
does not appear to control the biosynthesis of saturated fatty acids directly.
In O. nubilalis, there are several steps involved
in the biosynthesis of pheromone from myristic
acid: ∆11 desaturation, in which myristate is converted to the pheromone precursor acids, Z11Archives of Insect Biochemistry and Physiology
May 2007
doi: 10.1002/arch.
PBAN Regulation in O. nubilalis
35
Fig. 4. Mean titers (and SEM) of (a)
labeled Z11-14:Acyl and (b) native
Z11-14:Acyl in the pheromone gland
of decapitated Z-strain Ostrinia nubilalis females, topically applied with D5Z11-14:COOH, and injected with either PBAN or saline. Means were derived from 6–8 replicates, with 6–8
glands per replicate. There were no significant differences among means of
any of the treatments.
14:Acyl and E11-14:Acyl (Roelofs et al., 2002), fatty
acid reduction, in which the pheromone precursor acids are converted to alcohols (Zhu et al.,
1996) and acetylation (Jurenka and Roelofs, 1989),
in which the pheromone acetate esters are produced. With regard to desaturation, our data show
that increased desaturation of myristate occurs in
the gland in the presence of PBAN, with more labeled pheromone and similar amounts of the precursor acids produced, compared to the saline
control. However, this increased desaturation of
myristate apparently comes at the expense of ∆11desaturation of palmitate, with PBAN-injected females showing a concomitant decrease (relative to
the saline controls) in labeled Z11-16:Acyl, a fatty
acid normally produced, but not reduced, in the
Archives of Insect Biochemistry and Physiology May 2007
doi: 10.1002/arch.
gland. This suggests that PBAN does not increase
the activity of ∆11-desaturation per se, but somehow increases the flux of myristate through ∆11desaturation.
Since PBAN does not cause an increase in production of saturated fatty acids, nor does it increase
the activity of chain-shortening of palmitate, the
increase in flux of myristate through ∆11-desaturation suggests that PBAN affects the activity
of a downstream enzyme in the biosynthetic pathway. Alternatively, PBAN could cause increased
mobilization of myristate from stores (predominantly triacylglycerols; Foster, 2004b). However,
this would probably increase the concentration of
palmitate (as palmitoyl-CoA) more, since triacylglycerol lipases in general tend to be stereospecific
36
Eltahlawy et al.
rather than substrate-specific (Benlohr and Simpson, 1996), and palmitate is far more abundant in
the gland of female O. nubilalis than myristate (Foster, 2004b). Thus, although more myristate may
be produced from increased chain-shortening, the
increase in palmitate concentration should also
yield increased production of Z11-16:Acyl, which
was not observed.
Of the two downstream biosynthetic processes,
fatty acid reduction and acetylation, an increase
in activity of the former seems more likely since
(Z)-11-tetradecenol titer does not increase in the
gland following decapitation (Foster, unpublished
data). Further support for the activity of fatty acid
reduction being influenced by PBAN was provided
by the topical application of labeled precursor
acid (D5-Z11-14:COOH). This showed that over
the first 0.75 h of the experiment, PBAN-injected
females produced more labeled pheromone than
did saline-injected ones. At 0.25 h, control females produced similar levels of labeled Z1114:OAc as PBAN-injected ones. However, they
produced significantly less native Z11-14:OAc.
Thus, total (labeled and native) Z11-14:Acyl reduced was greater in PBAN-injected, than in control, females. Moreover, while labeled Z11-14:Acyl
titer was fairly constant over the 1.5 h of the experiment for saline-injected females, it increased
from 0.75–1.5 h for PBAN-injected ones; i.e., in
the same period that labeled Z11-14:OAc decreased. This suggests that the principal effect of
PBAN on fatty acid reduction occurred within the
first 0.75 h after injection, allowing increased flux
of myristate through ∆11-desaturation and therefore increased production of pheromone. Then,
as the effect of PBAN on fatty acid reduction decreased, probably due to degradation of the neuropeptide (Weirich et al., 1995), the level of
labeled Z11-14:Acyl increased until the flux of
myristate through ∆11-desaturation slowed, possibly due to inhibition by increased glandular
acyl-CoA concentrations (Foster, 2004a). Thus, the
flux of myristate through ∆11-desaturation appears
to be controlled indirectly by fatty acid reduction.
Control of fatty acid reduction by PBAN has also
been demonstrated in several other species of
moths (Martinez et al., 1990, Fabrias et al., 1995,
Ozawa and Matsumoto, 1996).
Through controlling fatty acid reduction, PBAN
is able to control the flux of fatty acids metabolized to pheromone in the gland. However, there
is no direct control of de novo fatty acid synthesis.
Although saturated fatty acid titers in the pheromone gland of female O. nubilalis show some diel
changes, with higher titers in the photophase than
in the scotophase, titers remain fairly constant for
a given time from day to day (Foster, 2004b). This
suggests that fatty acids are not synthesized continuously (otherwise titers would increase over
time), but that some modulation of this process
occurs. In O. nubilalis, when PBAN release ceases,
acyl-CoA concentrations should increase in the
gland, since the upstream processes continue producing fatty acids that will not be metabolized directly to pheromone. High acyl-CoA concentrations
inhibit the activity of acetyl CoA carboxylase, the
enzyme that catalyzes the first committed step in
fatty acid synthesis (Salati and Goodridge, 1996).
Such an inhibition would, therefore, modulate the
synthesis of fatty acids in the gland. Thus, we believe that pheromone biosynthesis in O. nubilalis
is modulated by a combination of hormonal factors and product inhibition. Future work will investigate potential product inhibition of fatty acid
synthesis.
ACKNOWLEDGMENTS
Thanks are due to Dr. Wendell Roelofs for the
suggestion of analyzing desaturase activity on
palmitic acid.
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