Don’t look now, they’re in your genes
This post is from regular guest blogger:
Ed Rybicki, Department of Molecular and Cell Biology, University of Cape Town, South Africa.
And they’re protecting you! If you’re an insect, that is. Or possibly a plant.
In a remarkable convergence of news, an Israeli group led by Ilan Sela described how Israeli acute paralysis virus, which is implicated in colony collapse disorder (CCD) in honeybees in the USA, can be found partially integrated into the genome of some honeybees in Israel. Which are then immune to the virus…
Plant virologists and biotechnologists are familiar with the term “pathogen-derived resistance” (PDR), which describes genetically-engineered resistance in plants derived by expression of parts of the pathogen genome. While this is theoretically possible for a wide range of pathogens, in practice it has most often been used against plant viruses – where some signal successes have been achieved. More recently, the phenomenon has been exploited in experimental strategies for defence against human pathogens, with RNA silencing constructs being successfully used to combat – among other things – HIV infection in cell cultures.
Now the Israeli group are claiming that a natural genetic engineering event – presumably mediated by reverse transcription into dsDNA from the viral ssRNA genome – is conferring protection against a lethal disease to certain populations of honeybees. This is an extraordinary claim, with extraordinary implications. If true, it is one of the first instances of proven PDR in insects, which opens up all sorts of possibilities for deliberate tinkering with the genomes of “companion” insects. However, it also points up some hitherto-unsuspected mechanisms for evolution of useful traits, which may be much more widely effective than we currently realise.
Because there’s more: Sela and colleagues also showed that host-derived sequences could be found in defective-interfering (DI) IAPV RNA molecules isolated from virus particles – meaning the virus could quite possibly transfer around bee genomic sequences, much as bacteriophages are known to do. In a related development, their group previously showed that Potato virus Y (PVY) sequences could be found integrated into the genome of several grapevine varieties – and in this paper they showed that DI RNA derived from PVY carried a stress-induced N. benthamiana gene fragment.
So plant and insect RNA viruses can insert parts of their genomes into their hosts, thereby potentially changing their phenotypes – but how? The group has an answer for that too: there is evidence that the viral sequences recombined with natural retrotransposons, possibly while these were in the RNA phase and being back-transcribed into DNA by their own reverse transcriptase.
I can’t actually say what this means better than the authors themselves: Man has been concerned with the possible hazards of virus-host RNA recombination. The authors agree with Falk and Bruening (1994) that man-engendered RNA recombination is statistically insignificant relative to the seemingly frequent natural process.
Think of that when next you insist on organically-grown non-GM food at your supermarket… those bugs you don’t want to kill are engineering your food as it grows – and they are changed in turn.
Degustibus non disputandum est indeed.
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[...] Don’t look now, they’re in your genes [...]
[...] possibility that certain non-retro RNA viruses can actually insert bits of themselves by obscure mechanisms into host cell genomes – and afford them protection against future infection – [...]