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A very interesting article.
I would recommend you to read it.
Virus gene engineer sends
caterpillars to a sticky end
Must climb… must climb… (Image: George Grall/Getty)
It takes just one gene to rule them all. With that gene, a voodoo virus
compels its caterpillar hosts to emerge from their shady hideaways, climb
en masse to the tops of trees, deliquesce and fall as a rosy rain of viral
particles on their fellow healthy caterpillars. Soon, they too will make the
climb of doom.
The virus is known as baculovirus and its unsuspecting host the gypsy moth
caterpillar. Like many other mind-controlling viruses, fungi and bacteria
that, for instance, turn ants into zombies and make rats unusually fond of
cats, baculovirus can selfishly change the behaviour of its host.
These bizarre relationships have long been documented but are poorly
explained: suspicions that many of the behavioural changes reflect changes
in gene expression have rarely led to genetic culprits.
Now researchers have found that the baculovirus uses a single gene to
force gypsy moth caterpillars to meet their sticky treetop end and infect
their relatives below.
Zombies by day
During the day, healthy gypsy moth caterpillars hide from birds and other
predators by staying near the soil, sticking to the underside of branches or
wedging themselves into crevices in tree trunks. Under the cloak of night,
they come out to feed.
In contrast, caterpillars that are infected with baculovirus climb up to
treetops in broad daylight, where they die because the virus has
commanded every cell in their body to make copies of itself.
As if that wasn't bad enough, the virus also produces enzymes that break
down the caterpillar's cell walls, liquefying it into oozing pink
puddles that swim with new viruses. The next time it rains, drops of water
pelt the puddles and carry viruses down the tree, where they infect other
caterpillars.
End of the road for a caterpillar ordered by a virus to turn to mush (Image: Michael Grove)
No more moulting
Kelli Hoover of Pennsylvania State University in University Park and her
colleagues suspected that the baculovirus uses a gene called egt to
change caterpillars' climbing behaviour. Egt codes for an enzyme that
inactivates an insect moulting hormone called 20-hydroxyecdysone. This is
useful because when caterpillars moult, they hunker down and largely stop
feeding – so are much less likely to climb trees, foiling the baculovirus's
plans.
Hoover infected gypsy moth caterpillars with six different strains of
baculovirus: two of the viruses were unmodified, two were missing egt and
two had had the gene removed and reinserted. Hoover placed the
caterpillars in tall plastic soda bottles with food at the bottom and a
fibreglass screen that the caterpillars could climb to reach the top.
Caterpillars infected with the normal baculovirus and the baculovirus with
the returned egt gene died at the top of the bottles, in the manner typical
of treetop disease. Caterpillars infected with the baculovirus missing the
gene did not demonstrate unusual climbing behaviour.
Vince D'Amico, an entomologist with the US Department of Agriculture
Forest Service, says the work is a first and key to advancing understanding
of how baculovirus is transmitted through gypsy moths.
Genetic weapon
Exactly how egt forces caterpillars to climb to the tops of trees is not
clear, but Hoover has some ideas. She notes that infected caterpillars
initially act like healthy ones: they only sprint to the treetops about 24 to
36 hours before the virus overwhelms all the cells in their body.
She thinks that once the virus has inserted its genes into the caterpillar's
cells, the enzyme for which egt codes gradually increases the amount of
inactivated moulting hormone in the caterpillar's body – and that this
build-up somehow triggers the unusual climbing behaviour.
In future, forest ecologists may be able to tweak baculovirus's genes to
control the gypsy moth, which is an invasive species in North America and a
major pest of hardwood trees, defoliating vast swathes of forest.
Researchers have tested baculoviruses as biopesticides in the past, but
found it worked too slowly compared with other pesticides. Genetically
modifying the virus – perhaps by duplicating egt – could turn it into the
gypsy moth's worst nightmare.
Virus gene engineer sends caterpillars to a sticky end - image 2 - life - 08 September 2011 - New Scientist
I would recommend you to read it.
Virus gene engineer sends
caterpillars to a sticky end
Must climb… must climb… (Image: George Grall/Getty)
It takes just one gene to rule them all. With that gene, a voodoo virus
compels its caterpillar hosts to emerge from their shady hideaways, climb
en masse to the tops of trees, deliquesce and fall as a rosy rain of viral
particles on their fellow healthy caterpillars. Soon, they too will make the
climb of doom.
The virus is known as baculovirus and its unsuspecting host the gypsy moth
caterpillar. Like many other mind-controlling viruses, fungi and bacteria
that, for instance, turn ants into zombies and make rats unusually fond of
cats, baculovirus can selfishly change the behaviour of its host.
These bizarre relationships have long been documented but are poorly
explained: suspicions that many of the behavioural changes reflect changes
in gene expression have rarely led to genetic culprits.
Now researchers have found that the baculovirus uses a single gene to
force gypsy moth caterpillars to meet their sticky treetop end and infect
their relatives below.
Zombies by day
During the day, healthy gypsy moth caterpillars hide from birds and other
predators by staying near the soil, sticking to the underside of branches or
wedging themselves into crevices in tree trunks. Under the cloak of night,
they come out to feed.
In contrast, caterpillars that are infected with baculovirus climb up to
treetops in broad daylight, where they die because the virus has
commanded every cell in their body to make copies of itself.
As if that wasn't bad enough, the virus also produces enzymes that break
down the caterpillar's cell walls, liquefying it into oozing pink
puddles that swim with new viruses. The next time it rains, drops of water
pelt the puddles and carry viruses down the tree, where they infect other
caterpillars.
End of the road for a caterpillar ordered by a virus to turn to mush (Image: Michael Grove)
No more moulting
Kelli Hoover of Pennsylvania State University in University Park and her
colleagues suspected that the baculovirus uses a gene called egt to
change caterpillars' climbing behaviour. Egt codes for an enzyme that
inactivates an insect moulting hormone called 20-hydroxyecdysone. This is
useful because when caterpillars moult, they hunker down and largely stop
feeding – so are much less likely to climb trees, foiling the baculovirus's
plans.
Hoover infected gypsy moth caterpillars with six different strains of
baculovirus: two of the viruses were unmodified, two were missing egt and
two had had the gene removed and reinserted. Hoover placed the
caterpillars in tall plastic soda bottles with food at the bottom and a
fibreglass screen that the caterpillars could climb to reach the top.
Caterpillars infected with the normal baculovirus and the baculovirus with
the returned egt gene died at the top of the bottles, in the manner typical
of treetop disease. Caterpillars infected with the baculovirus missing the
gene did not demonstrate unusual climbing behaviour.
Vince D'Amico, an entomologist with the US Department of Agriculture
Forest Service, says the work is a first and key to advancing understanding
of how baculovirus is transmitted through gypsy moths.
Genetic weapon
Exactly how egt forces caterpillars to climb to the tops of trees is not
clear, but Hoover has some ideas. She notes that infected caterpillars
initially act like healthy ones: they only sprint to the treetops about 24 to
36 hours before the virus overwhelms all the cells in their body.
She thinks that once the virus has inserted its genes into the caterpillar's
cells, the enzyme for which egt codes gradually increases the amount of
inactivated moulting hormone in the caterpillar's body – and that this
build-up somehow triggers the unusual climbing behaviour.
In future, forest ecologists may be able to tweak baculovirus's genes to
control the gypsy moth, which is an invasive species in North America and a
major pest of hardwood trees, defoliating vast swathes of forest.
Researchers have tested baculoviruses as biopesticides in the past, but
found it worked too slowly compared with other pesticides. Genetically
modifying the virus – perhaps by duplicating egt – could turn it into the
gypsy moth's worst nightmare.
Virus gene engineer sends caterpillars to a sticky end - image 2 - life - 08 September 2011 - New Scientist