How plants and animals steal genes from other species to speed up evolution

Grassland in Uganda. Credit: Luke Dunning, author provided

little did biologist Gregor Mendel know that his experiments with sweet peas in the garden of a monastery in Brno, Czech Republic, will lay the foundation for our understanding of modern genetics and heredity. His work in the 19th century helped scientists establish that parents transmit their genetic information on their offspring, and in turn, they pass it on to their own.

Indeed, this premise forms the basis of much of our understanding of evolution. But we now know that this process is not sacrosanct and that some of our most cultured cultures can trick the system by supplementing their genetic information with stolen genetic secrets. Our new study, Posted in New Phytologistshows that this actually happens in grasses.

However, grasses are not the only culprits. Bacteria are the criminal masters in this regard. They are able to freely absorb genetic information from their environment. This process is called lateral or horizontal gene transfer, and it is thought to play an important role in the spread of traits such as antibiotic resistance.

Although scientists originally thought this process was limited to bacteria, it has since been documented in a wide range of animals and plants. Examples include aphids which can synthesize red fungal pigment to avoid predation, fungi that have shared genetic instructions to assemble psychoactive compounds, and the whiteflies that have turned against them the defenses of their host plants.

Mysterious gene transfer

Grasses are the most ecologically and economically important group of plants. Grass cover between 20% and 40% of the world’s landmass, and several of the world’s most widely grown crops are grasses, including rice, corn, wheat, and sugar cane. Our new study is the first to show that lateral gene transfer is widespread in this important group of plants, and that it occurs in both wild and cultivated species.

Our discovery is based on genetic detective work, helping us trace the origin of every gene in the genomes of 17 grass species from around the world. As expected, an overwhelming majority of genes had the same evolutionary history as that of the species they were found in, indicating that they were passed down from generation to generation, from parents to descendants. However, we found over a hundred examples where the evolutionary history of species and genes did not tell the same story.

The results showed that these genes had a past life in another distant grass species before being transferred into the recipient’s genome.

We know that species boundaries are inherently porous, and that hybrid can occur resulting from reproduction between closely related organisms. Hybridization and lateral gene transfer ultimately have similar effects generating new gene combinations that may or may not be advantageous.

However, lateral gene transfer is not a reproductive process and therefore has the potential to connect deeper branches in the tree of life, facilitating the movement of genetic material over much larger evolutionary distances. Genes transferred between grass species have functions related to energy production, stress tolerance and disease resistance, potentially giving them an evolutionary advantage by allowing them to grow bigger, taller and stronger .

Foreign DNA was detected in the genomes of 13 of 17 grasses sampled, including crops such as corn, millet and wheat. The million dollar question is: how do these genes move between species? In truth, we do not know and may never know for sure because there are several potential mechanisms and more than one may be involved.

After all, evolution studies events that happened thousands, if not millions, of years ago. But there is a significant statistical increase in the number of transferred genes present today in grass species with rhizomes—modified roots that allow plants to propagate asexually (a process in which part of a plant can be used to generate a new plant). DNA transfer in the rhizome could be facilitated by direct contact between subterranean species, possible through root fusion. Interestingly, scientists have recently observed DNA moving between tobacco plants that were grafted together, further supporting this hypothesis.

Any foreign DNA transferred into the rhizome would then be replicated in all cells of the daughter clone from that tissue when the plant reproduces asexually. This foreign DNA would then make its way into the germ line (cells that pass their genetic material to offspring) and into future generations when the clone daughter flowers and sets seed.

How plants and animals steal genes from other species to speed up evolution

Luke Dunning investigates weed in Sri Lanka. Author provided

GM debate

The results of this study show that grasses have themselves been genetically modified. Whether this is ammunition for the pro or anti-GMO lobby depends on your existing preconceptions in this debate.

You could say that if grasses already do it naturally, then why not us? Conversely, this research shows that genes can move freely between grass species, regardless of their relatedness. Therefore, any gene inserted into a modified grass may eventually escape into wild species generating what are known as super weeds.

Ultimately, if we can determine how lateral gene transfer occurs in grasses, it may allow us to harness the process so that we can naturally modify crops and make them more resilient to the effects of climate change.

Naturally GM: crops steal genes from other species to speed up evolution

More information:
Samuel GS Hibdige et al. Widespread lateral gene transfer among grasses, New Phytologist (2021). DOI: 10.1111/nph.17328

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