Thieving grasses skip evolution

21 February 2019

GRASS-FIELD

The image shows a field at sunset.

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Scientists have discovered that some grass species are shortcutting evolution and instead stealing genetic information from neighbouring plants. By genetically modifying themselves, they gain a competitive edge, which helps them thrive in more challenging environments...

The species Alloteropsis semialata, a type of tropical grass found in Africa, Asia and Australia, has changed the way it produces energy, a process known as photosynthesis. Intrigued by this phenomenon, a group of international researchers lead from the University of Sheffield, investigated further: “the enzymes it uses for this new photosynthetic pathway are actually borrowed from other species, so this gave us a clue that, hang on, something untoward was going on”, explained the lead author Luke Dunning. The findings of these thieving grasses were recently published in the Proceedings of the National Academy of Sciences (PNAS).

As a group of species, grasses are essential to humans, not just because they are the surface for many popular sports like football and golf, but because they are a source of food for people all around the world. They include some of our staple foods - wheat, maize, rice, barley and sugar cane, and so grasses are incredibly important both ecologically and economically.

After collecting samples of Alloteropsis semialata from Australia, the team sequenced the plant’s genome, which is the plant’s complete set of genetic instructions. By comparing this genome to that of another 147 grass species, the scientists surprisingly found that it has slight differences in its genetic makeup compared to its ancestors, and that Alloteropsis semialata actually contains foreign genes from very distant species. The discrepancies in normal evolution indicate the genes were acquired laterally, rather than through previous plant generations.

Dunning suggests two working theories for this: “illegitimate pollination - the grass species are too distantly related to actually hybridise, but its pollen can still land on one species from the flower of another.” Or Dunning’s second theory is: “root to root contact - grasses can reproduce through rhizomes, these bulb structures underground. Potentially if roots from one species were able to grow through the rhizomes of another, there could be a little DNA transferred into the stem cells [cellular template] which then go on make the plant.” Both theories lean on direct contact during reproduction as a route to incorporating foreign DNA, resulting in seeds with both the parents’ genome and a little of the stolen DNA.

But do these thieving plants actually pose a risk? “What we’re seeing is a natural phenomenon, so it’s not a problem as such, but it does have implications for the use of genetically modified (GM) crops, and that depends on your viewpoint.” GM crops could be viewed as more natural than we think, since wild plants are doing this already. Or, on the contrary, genes from GM crops could more easily escape to weed species which may have knock on effects. Regardless of your viewpoint on this gene robbery, the findings are contributing to our understanding of the theory of evolution. The basis of Darwin’s theory is that all life descends from a common ancestor, but perhaps now we should include neighbouring species as a contributor to evolution.

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