DNA. Deoxyribonucleic acid. It's the
genetic material that's in the cells of
all living organisms. It's the double
stranded helix structure in cell nuclei
that carried the genetic information of
an organism. It consists of thousands of
genes that are made up of millions and
billions of pairs of nucleotides.
Each gene is a set of instructions on how to
build a protein molecule, but in order to
make a protein from DNA, there's another
player - Messenger RNA. DNA is copied into
mRNA. RNA ribonucleic acid, a
single-stranded sort of mirror image
temporary version of DNA. This mRNA
transfers the DNA message from the
nucleus to the ribosomes - where the
proteins are manufactured. The mRNA is
then translated into proteins and in
turn these proteins do things. They are
the workhorses for cellular and organism
function. Taken together, DNA, RNA, and
proteins are the blueprints and raw
materials for life. Knowing that these
molecules exist in living organisms and
how they work gives humans some powerful
tools for manipulating the genetics of
organisms.
Well, this brings up another
molecule involved. It's a version of RNA,
that temporary copy of the DNA, called
RNAi. The 'i' in RNAi stands for
interference. When a cell wants to stop
making a protein, it produces a little
RNAi molecule which silences certain
DNA from producing a protein. RNAi is a
naturally occurring necessary genetic
component of all organisms including
humans. For example, RNAi has the
important job of fighting things like
viruses and regulating genetic changes
and mutations. RNAi does this by
specifically targeting certain sequences
of DNA and blocking the production of
proteins. Since the discovery of the RNAi
process in the 1990s, this genetic
mechanism has led to some pretty
innovative applications. Application of
RNAi has shown to be a promising method
of improving life for us on many levels,
including switching off genes that cause
diseases, learning what genes do and
how they work, and making food production easier.
Researchers use RNAi by
designing and introducing short strands
of RNA. Around 21 to 25 nucleotides these,
short strands bind to the complementary
sequences in the genetic code. RNAi
works by stopping the information in the
DNA from getting to the protein making
ribosomes. It interferes with a messenger RNA.
When it comes to agricultural
applications, RNAi can be used as a form
of genetic pesticide that can be built
right into a plant's biology. For example,
an insect pest feeds on a crop that
deploys RNAi coded to stop the ability
for that pest to digest food and process
nutrients from the plant.
As a result, the
pest growth or its ability to reproduce
is slowed or halted or the pest dies.
Or a crop produces RNAi that changes a
plant's chemistry, making that plant
unattractive to a pest or the RNAi can
block a plant's susceptibility to an
herbicide allowing the herbicide to only
kill weeds on the farm. When we consider
how society relies on crops for food,
fuel, and fiber, it's easy to see why RNAi
can be a valuable asset in crop
improvement, and a powerful tool against
yield loss. However, just as when using
other powerful tools, we have to make
sure that the technology is safe. Keep in
mind that genes are made up of millions
and billions of pairs of nucleotides, and
RNAi targets gene sequences around 21
to 25 nucleotides long. That's right,
21 nucleotides in a sequence out of
billions in a gene. With those kinds of
odds, the chances of the RNAi blocking
other RNAs from producing totally
unpredicted proteins is likely.
One possible risk is that the RNAi molecule
might silence the correct gene, but in
the wrong organism. It turns out that the
RNAi and the RNA don't have to be 100%
identical for there to be silencing. For
example, in addition to silencing part of
a corn pest's digestive system, maybe an
RNAi molecule would accidentally
silence part of the digestive
system of a lady beetle or a honeybee or
a cow or cousin Mabel. These risks are
not trivial. Especially because they're
different from those posed by most other
types of pesticides that we're used to
dealing with. Now, considering the
unintentional turning off of unintended
genetic functions of targeted and non
targeted organisms and the huge
complexity of biological and ecological
systems on which all life depends, this
could be a bit of a problem.
Without more
knowledge about how pesticidal RNAi
works in pests and non-target organisms
it's difficult to predict how this
technology might affect the environment.
Sounds dire, right?
Well, it doesn't have to be.
To manage these risks, we can
already take some unknowns out of the
equation to make sure that the
pesticidal RNAi poses minimal threats
to the species that we want to stick
around.
When you want to eliminate the unknown, what do you need?
More data.
You have to take steps to weed out RNAi
that silences genes other than the one
you mean to target, and be sure the genes
they target are really involved in the
cellular function of interest.
So assessing an area's bio inventory can
help. Then we'll know what species might
be exposed to RNAi. Also, we'll get the
genomes or genetic blueprint for the
exposed species and screen potential RNAi molecules to see whether a particular
pesticide might hurt the species we want
to keep healthy.
From this, we can develop
comprehensive risk assessment procedures
that can make sure our desire to manage
pests isn't coming at the expense of
Mother Nature.
Science can help us to
understand the benefits and risks
associated with this amazing new
technology called RNAi and where it
fits in with a sustainable and long term
successful plan for agriculture.
For more information on RNAi based insecticides,
refer to articles published in
Bioscience Magazine and online
at igrow.org.
