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.