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Police forensic science supportFarmers like genetically engineered (GE) crops because they require less pesticides and fertilizers than conventional crops. This allows farmers to save money, time, and also the environment.

One of the most famous GE technologies, Bt, introduced a gene that makes plants insect-resistant. Plants produce a protein, named Cry, which is toxic for insects but does not affect humans. This technology eliminates the need for indiscriminate fumigation of entire fields.

Bt technology was developed during the 90’s; cleaver as it is, a new technology just down the corner could make it look like a VHS recorder.

RNA interference (RNAi) technology is a tool so precise and accurate that will be more effective and even safer for humans and the environment than first-generation GE insect-resistant crops (1). How does it work?:

CSI viewers and crime-stories’ fans know that DNA fingerprints are so personal that they allow pin-pointing of individuals. Biologists also use DNA sequencing to identify species and families of species, even extinct species.

DNA doesn’t do much work in the cells though; it is more like a DIY book that cells read to know what to do. DNA contains instructions on how to make proteins. Proteins are the real players in the cells.

MM566Proteins do all the work: they convert food into energy and energy into fat stores; they build the cell membranes and defence systems; they even make more proteins*. This is a key point for the new technology. Before protein-making proteins can read instructions encoded in DNA, the instructions need to be transcribed into RNA code. RNA is a molecule closely related to DNA. Proteins that make more proteins read their instructions from RNA.

MM565RNA is neither protein nor DNA; RNA is RNA. It carries the same message as DNA but the message is written in different characters, like books in Greek and English. Taking the analogy further, it would be as if proteins that make proteins could read “English” (RNA) but not “Greek” (DNA).

In 1998 Fire and Mello discovered that there was a second type of RNA (RNAi), an anti sense RNA with instructions written upside down. This RNAi prevented protein workers from reading normal RNA, even causing it to be destroyed. This prevents the building of proteins. In normal circumstances RNAi is used by cells for regulating processes after DNA has been transcribed into RNA and for fighting viruses. Fire and Mello received the Nobel Prize in 2006 for their discovery.

DNA and RNA share important characteristics; they are equally written in a 4 letters code of nucleic acids and are very particular of each species or families of species. For this reason, RNAi could be used to target specific pests leaving any other species untouched. For example, plants could produce an RNAi that selectively kills a nasty insect, such as the corn borer, leaving pollinators completely unharmed (1).

Several universities and companies are now competing to develop and commercialize RNAi GE technology and to deliver an insecticide with a scalpel’s precision.

Read also Kai Kupferschimidt excellent article in Science Magazine VOL 341 p732-3 (You will need a subscription)

You can listen to Science Magazine Podcast about pesticides for free

* To be more precise proteins are built by ribosomes, large and complex cellular machines formed by proteins and rRNA.

(1) Applied Biochemistry and Biotechnology 2013

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  • Beibei 14/05/2014 at 5:13 pm

    Hello Ariel,
    Interesting idea. I have a question about the RNAi delivery methods you proposed.
    1) If you spray RNAi, I wonder how efficient it can be absorbed by the plant through their cell walls;
    2) How would you make transgenic plants that produce their own anti-insect RNAi, and how such these particular anti-insect RNAi can be reproduced in the next generations.
    Thanks for answering my questions!

    • Ariel Poliandri 14/05/2014 at 8:38 pm

      Hi Beibei
      In reply to your questions:
      RNAi can be sprayed in solution like any chemical. It doesn’t need to get inside the plant; the insects will eat it on the plant. There are two problems with this approach though.
      1. production of RNAi -and RNA generally- is very expensive at the moment and you will have to spray a lot.
      2. for spraying you need to use machines that work with fossil fuels which is expensive and releases CO2.
      Let alone that RNA doesn’t last much outside cells; it gets degraded very easily.
      If the plants produce their own RNAi you can bypass these problems.
      iRNA -like any other RNA- uses DNA as a template. You just introduce the DNA sequence codifying for the particular RNAi into the plant’s genome and the plant uses its own transcription machinery to make the RNAi. The DNA sequence for RNAi is transmitted to the daughter plants with the rest of the genome.
      I hope this answers your questions.
      Cheers

  • nesamalar durai 01/09/2013 at 7:51 am

    Ariel: On the next generation insect resistant plants i applaud you. but my question is how is it made to be insect resistant? Please clarify this.
    Thank-you.
    PS Please not sure the value??? What is wanted.

    • Ariel Poliandri 01/09/2013 at 7:52 am

      Hey Nesamalar,

      What we want is food security. We need crops that are pest-resistant but we want to have -ideally- as little impact as possible on the environment.

      How RNAi will work:
      First you look for a gene (or combination of genes) that is indispensable for the insect-pest survival. Genes are essential because the proteins that they encode are essential. Remember: Proteins do all the work; genes only carry instructions of how to make proteins.

      Then you design an RNAi that interferes with the instructions provided by the gene.

      -Look at fig. 2 in the post. RNA is an intermediary product required for making proteins from DNA. Your RNAi blocks the instructions carried by a specific RNA (they stick together and generally are destroyed). Without the instructions in the DNA-related RNA the protein cannot be made.

      As the insect needs to make this protein to live, it dies.

      As RNAi is very similar to DNA you can find RNAi sequences that are particular to just that insect. This RNAi will not affect the product of the same gene(s) in different species.

      There are two ways of RNAi delivery. You either spray the plants with RNAi or make transgenic plants that produce their own anti-insect RNAi.

      An extra safety mechanism is that mammals do not internalise RNAi from food but insects do. The explanation for this deserves another post altogether but basically this is because our digestive systems are very different. For example RNAi (being so specific) could be used to kill cancer cells. However, up to now it has been very difficult to find a way to deliver RNAi into the human body to do that job.

      Hope this answers you question.

  • Jerry Hoebink 28/08/2013 at 4:33 pm

    RNAi seems to be less harmful to the environment than pesticides, and less damage by insects increases the amounts of crops being grown, which is very convenient with the growing world population. The effect upon the ecosystem should be checked. As insects which cause damage to crops, tend to be the prey of others animals, i.e. birds, which tend to be the prey of bigger

    • Ariel Poliandri 28/08/2013 at 4:35 pm

      Jerry: I hope this is allowed field trials. The main selling point of the technology is that it targets pests that shouldn’t be there in the first place. RNAi against a particular species shouldn’t affect others, leaving the ecosystem untouched.
      In addition, mammals (not sure about birds) do not even take up RNAi from food; if they did gene therapy would be a lot easier…

  • Trista Powell 27/08/2013 at 4:11 pm

    LinkedIn comment:
    Using RNAi against specific insects is a great idea because some people actually have allergies against some pesticides. As long as it supports the ecosystem in a good way that is all that matters.

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