Friday, 25 May 2012

Coffee Berry Borer Beetle not so boring when it comes to swapping genes.



Coffee berry borer Beetle on its favourite food (coffee bean).

When one thinks of natural gene transfer in organisms, the most common process that comes to mind is that of the transfer of genetic material from parent to offspring – a process that occurs in any example of reproduction. While this certainly is the most common form of genetic transfer, genes may also be shared between independent organisms of different lineages in a process known as Horizontal Gene Transfer (also known as Lateral Gene Transfer). This process is much more commonly witnessed between two prokaryotes rather than between a prokaryote and eukaryote or two eukaryotes, and when it does involve eukaryotes, it is usually in very simple organisms. One famous example of the latter occurring is in the eukaryotic absorption of endosymbiotic organelles early in our own evolution. An article published on the Nature website in February 2012 describes a study examining the possibility of prokaryotic contribution to the genome of the Coffee berry borer Beetle, the findings of which suggest that a previously unseen type of protein-encoding in insects has been transferred in potentially relatively recent times.

The beetle, Hypothenemus Hampei, originally from Africa, is an agriculturally important pest responsible for worldwide coffee crop losses in excess of 500 million USD. While similar coffee-bean consuming insects exist, H. hampei is the only one known to be able to feed exclusively on the beans. This is due to the beetle’s ability to produce a polysaccharide-digesting enzyme known as mannanase, the genetic controller of which (a gene known as HhMAN1) appears to have been acquired through HGT with the beetle’s gut flora. While some plants and animals are known to be able to produce a type of mannanase, the type produced by H. hampei is thought to be much more commonly related to that of prokaryotes. In addition, the HhMAN1 gene in the H. hampei’s genome is surrounded by transposons – sequences of DNA able to be easily transposed – a situation possibly evident of the insertion of external DNA from the bacteria.

What makes the discovery particularly interesting and somewhat unique is the obviously functional role of the gene in the beetle. Previously discovered eukaryotic genes thought to be present due to HGT have shown little obvious benefit to the organism, but the presence of mannanase in H. hampei and its ability to survive on coffee beans alone allows it to take maximum advantage of a relatively unoccupied ecological niche. The authors of the study go so far as to say that while H. hampei acquired HhMAN1 before dispersing from Africa, recent human agricultural practices surrounding coffee production may have acted as a significant selective evolutionary pressure in favour of the beetle, potentially reflecting a phenomenon and threat in other spheres of the agricultural industry due to increasing monoculture in general.

Link to the article on Nature:
And the original study:

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