Fighting Colorado potato beetle with RNA interference -- ScienceDaily

Feeding experiment with different potato leaves: Detached leaves of unmodified plants were compared to plants with an altered chloroplast genome. First instar larvae were fed on these leaves for three days in intervals of 24 hours. The leaves were replaced after each interval.

Credit: © Sher Afzal Khan, Max Planck Institute for Chemical Ecology

Fighting Colorado potato beetle with RNA interference

Date:February 26, 2015 Source: Max Planck Institute for Chemical Ecology

Summary:

Colorado potato beetles are a dreaded pest of potatoes.
Since they do not have natural enemies in most regions, farmers try to control
them with pesticides. However, this strategy is often ineffective because the
pest has developed resistances against nearly all insecticides. Now, scientists
have shown that potato plants can be protected from herbivory using RNA
interference.

lorado potato beetles are a dreaded pest of potatoes all
over the world. Since they do not have natural enemies in most potato producing
regions, farmers try to control them with pesticides. However, this strategy is
often ineffective because the pest has developed resistances against nearly all
insecticides. Now, scientists from the Max Planck Institutes of Molecular Plant
Physiology in Potsdam-Golm and Chemical Ecology in Jena have shown that potato
plants can be protected from herbivory using RNA interference (RNAi). They
genetically modified plants to enable their chloroplasts to accumulate
double-stranded RNAs (dsRNAs) targeted against essential beetle genes.
(Science, February 2015).

RNA interference (RNAi) is a type of gene regulation that
naturally occurs in eukaryotes. In plants, fungi and insects it also is used
for protection against certain viruses. During infection, many viral pathogens
transfer their genetic information into the host cells as double-stranded RNA
(dsRNA). Replication of viral RNA leads to high amounts of dsRNA which is
recognized by the host's RNAi system and chopped up into smaller RNA fragments,
called siRNAs (small interfering RNAs). The cell then uses siRNAs to detect and
destroy the foreign RNA.

But the RNAi mechanism can also be exploited to knock down
any desired gene, by tailoring dsRNA to target the gene's messenger RNA (mRNA).
When the targeted mRNA is destroyed, synthesis of the encoded protein will be
diminished or blocked completely. Targeting an essential gene of a crop pest
can turn dsRNA into a precise and potent insecticide.

Some crop plants have recently been engineered by modifying
their nuclear genomes to produce dsRNA against certain insects. "This
never resulted in full protection from herbivory," says Ralph Bock of the
Max Planck Institute of Molecular Plant Physiology, "because the plant's
own RNAi system prevents the accumulation of sufficient amounts of dsRNA. We
wanted to circumvent this problem by producing dsRNA in the chloroplasts
instead." These organelles, which perform photosynthesis in green plants,
are descendants of formerly free-living cyanobacteria, which are prokaryotes
that lack an RNAi system. Presuming that chloroplasts would accumulate high
amounts of dsRNA, the scientists in Ralph Bock's group decided to generate
so-called transplastomic plants. In such plants, the chloroplast genome is the
target of genetic modification instead of the nuclear genome.

To test this system on a real insect pest, the scientists
chose the Colorado potato beetle. This little striped beetle was introduced
into Europe accidentally at the end of the 19th century. Nowadays, it is a
worldwide pest and can cause massive damage in agriculture. Besides potato
leaves the adult beetle and its larvae also feed on other nightshade crops,
like tomato, bell pepper and tobacco. The pest is difficult to control because
of the widespread occurrence of insecticide resistance. "By using
chloroplast transformation we generated potato plants that accumulate high
amounts of long stable dsRNAs targeting essential genes in the beetle,"
says Ralph Bock.

The efficacy of the dsRNAs as an insecticide was tested at
the Max Planck Institute for Chemical Ecology in Jena. Larvae were fed on
detached potato leaves and the mortality was monitored for nine days. The
leaves were taken from transplastomic dsRNA plants, conventional transgenic
dsRNA plants with a modified nuclear genome, and unmodified plants. For
comparison, dsRNAs targeting two different genes were tested.
"Transplastomic leaves producing dsRNA against the actin gene caused a
mortality rate of 100% after five days of feeding," says Sher Afzal Khan
from Jena. The actin gene encodes a structural protein that is essential for
cell integrity. In contrast, plants with a modified nuclear genome expressed
much less dsRNA and only slightly slowed down the beetles' growth.

These recent results show that changing the target of
transformation from the nuclear genome to the chloroplast genome overcomes the
major hurdle towards exploiting RNAi for crop protection. As many insect pests
increasingly develop resistances against chemical pesticides and Bt toxins,
RNAi represents a promising strategy for pest control. This technology allows
for precise protection without chemicals and without production of foreign
proteins in the plant.

Story Source:

The above story is based on materials provided by Max Planck
Institute for Chemical Ecology. Note: Materials may be edited for content and
length.

Journal Reference:

Zhang, J., Khan, S. A., Heckel, D. G., Bock, R. Full crop
protection from an insect pest by expression of long double-stranded RNAs in
plastids. Science, February 2015 DOI: 10.1126/science.1261680

Source Max Planck Institute for Chemical Ecology. "Fighting
Colorado potato beetle with RNA interference." ScienceDaily. ScienceDaily,
26 February 2015.
<www.sciencedaily.com/releases/2015/02/150226144859.htm>.

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