article 01: Self-defence for plants - agriFuture

Research & Innovation
Self-defence for plants
Insects are our greatest
competitors for food on
this planet. Not only do they
consume or spoil huge
amounts of plant product
both in the fields and in storage,
they’re also the most
important vectors of plant
disease. But some of them,
those that prey on crop insect
pests or help pollinate,
are among the most beneficial
of creatures, at least
from the point of view of
man. Without their pollination
input production of
fruit, vegetables or oilseed
rape would be greatly
reduced, as would our
daily diet. With this background,
bees – after pigs and
cattle – are the third most
important »farm animals«
from the agro-economy
aspect.
But insects could be even
more useful to mankind.
And there’s a raft of molecular
biology and biotechnology
developments now
ready to help in this direction.
For farming, these new
technologies offer environmentally-friendly
strategies
for plant protection, selective
destruction of the important
insect pests, protection
of beneficial insects and
other non-target organisms
(and that includes you and
me).
Helping here is RNA
Interference Technology
(RNAi), an approach that
genetically modifies a
plant so that it can destroy
a particular insect
pest through deactivation
of a selected gene in the
organism.
Insect biotechnology
could help quite soon in
the control of the rape
pollen beetle - without
threatening beneficial
organisms.
Mit Hilfe der
Insektenbiotechnologie ist
es vielleicht bald möglich,
den Rapsglanzkäfer zu
bekämpfen, ohne dabei
Nützlinge zu schädigen.
Avec l’aide des
biotechnologies, il sera
peut-être bientôt possible
de maîtriser le méligèthe
sans nuire aux auxiliaires.
Krause
24 agrifuture Winter/11

The difference between the RNAi and Bt toxin concepts
Just like the RNAi approach, the Bt technique also involves
the plant protecting itself »from within«. Both
also feature gene technology whereby plants produce
their own »insecticide« for protection against pests.
But with Bt the necessary gene has not been »donated«
by an insect. Instead it comes from a bacterium
(Bacillus thuringiensis). Inserted in the plant, this gene
enables the synthesis of the required Bt toxin. Bt toxins
are very specific in their effect against a certain insect
(group). Bees, for instance, have no receptors for Bt
proteins and are therefore not negatively affected.
Some trials with Bt toxins against the European corn
borer show, however, that other types of butterfly, such
as the monarch, can be damaged. This has caused a lot
of controversy, even although the damaging effect
through Bt maize pollen is insignificantly small.
The RNAi technique offers two important advantages
landpixel
over the Bt
concept.
Firstly, the
risk of resistance
becoming
established
is
markedly
less. A mutation
in the target organism causing loss of efficacy is
much more improbable than with Bt. And secondly,
the RNAi technique offers a still higher target organism
specificity than Bt. This is because a much more specific
sequence area is selected, an area that has no
similarities with other potential organisms. Guaranteeing
this specificity, however, involves intensive and
very thorough preparation work.
Insects in industry and medicine
The enormous economic and innovative potential of insect biotechnology is
currently highlighted through its application in industry and medicine. Industry
has particular interest in new enzymes. An example is the production
of biofuels from energy crops and other green materials. Enzymes are required
in this process to help efficient degradation of cellulose and lignin
and these are often produced from fungi living in symbiosis with wood eating
insects. Within the research focus on insect biotechnology, highly efficient
wood degrading enzymes e.g. in symbiotic fungi from wood wasps and
wood beetles, are therefore urgently »wanted«. Furthermore, industry is also
deeply interested in the potential of molecules from insects which can be
applied in the conservation or processing of food. Thus in the saliva of the
burying beetle Nicrophorus vespilloides has been found a series of conservation
substances with which the insect can protect the body of a dead mouse
from microbial degradation until it can be utilised for feeding its young.
In medicine there’s substantial demand for new antibiotics because of the
threatening growth of pathogen resistance to currently used antibiotics.
Now being tested are antimicrobial peptides from insects to assess their effect
on bacteria that have become resistant to antibiotics. Additionally to be
tested in mouse models is whether anti-infectives produced by insects may
be suitable to application in clinics. The organisms to be more closely examined
in this context include the maggot of the blowfly Lucilia sericata. The
maggots are multiplied under sterile conditions and are already applied
worldwide in the treatment of wounds that are no longer treatable using
standard disinfectants.
agrifuture Winter/11 25

Research & Innovation
Rapeseed is Europe’s mostgrown
oil plant and, after
soybeans, the most important
oilseed worldwide. Expansion
and intensification
of its production, often in association
with low-till or notill
regimes, means the
crop’s a growing target for
insect pest damage. One example
is the massive increase
in rapeseed pollen
beetle population bringing
with it yield penalties of up
to 50%. But anyone who
knows rapeseed also knows
there are plenty of other important
pests waiting on the
wings including diverse
weevils (rape stem weevil,
cabbage seed weevil), flea
beetles (rape flea beetle,
cabbage stem flea beetle),
turnip or cabbage root flies.
With increased pest populations
comes more spraying
and then pesticide resistance.
One reaction is integrated
plant protection with
treatment only when economic
damage thresholds
are breached. But every sign
now indicates this solution
is also reaching its limits.
This is where insect biotechnology
can help. It’s a
huge, largely unexplored,
field. Just consider: There are
around a million species of
insects already discovered.
And it’s estimated that about
the same number have yet to
be identified. Insects are
easily the most species-rich
sector of the animal kingdom,
occupying just about
every conceivable ecological
niche on the planet.
What RNAi offers is highly
specific control of the crop
pests within these myriad
species. Its application allows
certain genes in insect
cells to be »switched off« or
deactivated by plant proteins.
The strategy is to select
the genes where deactivation
leads to insect death.
Scientists are using model
insects such as the rice flour
beetle Tribolium castaneum
for identification of suitable
genes. Genome sequencing
First success
First research results show that the RNAi approach,
already successfully applied in medicine and biology,
also offers great possibilities for plant protection.
The technique allows protection of plants
against insects, nematodes or fungi through highly
selective destruction of the identified pest. Under
laboratory conditions an induced resistance of
maize against western corn rootworm has already
been demonstrated. Similar success in resistance
against boll weevil in cotton has been observed.
This last is a pest that has succeeded through evolution
in developing a process for detoxifying the poison
gossypol produced as natural protection by the
cotton plant. By identifying the insect proteins that
are involved in the detoxification procedure it has
then been possible to apply RNAi to reduce their
efficacy. The result is a healthy cotton plant which,
with the help of its »new« defence, can once again
protect itself against the boll weevil. And there are
numerous other examples of successful applications
of the RNAi concept in plant protection.
Krause
To make the new
technology useful in
practice, the genome of
all rapeseed insect pests
should first of all be
examined. Here,
rapeseed pollen beetles
are fed with pollen
including transferred
dsRNA.
Um die neue Technologie
praxistauglich zu
machen, müssen
zunächst die Genome
sämtlicher
Rapsschädlinge
untersucht werden. Im
Versuch werden dazu
z. B. Rapsglanzkäfer
über Blütenpollen mit
dsRNA gefüttert.
Pour permettre la mise
en œuvre sur le terrain
de la nouvelle
technologie, il faut
d’abord analyser le
génome de tous les
ravageurs du colza. Dans
cet essai, les méligèthes
sont nourris avec de
l’ARN (acide
ribonucléique) double
brin grâce à du pollen.
has already been completed,
or almost finished, in
over 50 species of insect.
The data collected permit
the targeted search for genes
that are found in only particular
groups of insects and
are essential for their development
and therefore ideal
candidates for »switching
off«.
To develop a rapeseed plant
that deactivates a pest, e.g.,
the rape pollen beetle, the
first thing to be done is to
identify a gene crucial to the
beetle’s survival. Then a
small segment of genetic information
taken from the
gene in question is transferred
into the oilseed rape
plant via the RNAi technique.
This transplant (a segment
of approx. 300 to 400
protein building blocks of
double-stranded RNA or
dsRNA) produces proteins
in the plant that can deactivate
the crucial gene in the
insect pest.
In that the beetle feeds
mainly on rapeseed pollen,
the dsRNA should be positioned
only in the plant pollen
cells. We then have a
gene segment with an effect
so specific that it will influence
only the rape pollen
26 agrifuture Winter/11

eetle. This last point is of
fundamental importance
and achieves innovative pest
destruction with a very high
specificity, even higher than
that achieved so far by existing
biotechnological processes
(e.g. Bt maize or cotton).
On top of this, the risk
of resistance developing is
lower than with the Bt concept.
These advantages for RNAi
(including exclusion of damage
to non-target organisms)
mean it should experience a
broader acceptance from
society. And of course there
are attractions for RNAi
technology outside of insect
pest control. Its role in pre-
cise inhibition of stress-induced
or stress-dependent
proteins in plants has the
potential of conferring increased
crop tolerance to
drought, heat, cold or ozone
in rapeseed or maize, possibilities
which guarantee an
exciting future for RNAi
technology in agriculture.
◆
Prof. Dr. Andreas Vilcinskas,
Institute for Phytopathology and
Applied Zoology, Prof. Dr.
Wolfgang Friedt, Peter Krause,
Institute for Plant Breeding,
University of Giessen
●
Vor allem im Rapsanbau stößt der Einsatz
herkömmlicher Insektizide an seine Grenzen.
Neue gentechnische Methoden könnten künftig
ganz neue Strategien ermöglichen, mit denen
Schadinsekten bekämpft werden können, ohne dabei die
Nützlinge oder den Menschen zu gefährden.
●
La culture du colza est la première concernée par
l’efficacité de plus en plus limite des insecticides
classiques. De nouvelles techniques de génie
génétique pourraient ouvrir de nouvelles perspectives
de lutte en contrôlant les ravageurs sans nuire aux
auxiliaires utiles ou à l’homme.