Researchers show that grasses frequently incorporate DNA from other species in a process called lateral gene transfer
When many people think about genetically modified crops, they think of altering plants in the lab so they can better cope with drought, disease and pests or be able to grow quicker.
However, genetic modification is actually a natural occurrence, and research led by the University of Sheffield is the first to show the frequency by which grasses incorporate DNA from other species in a process called lateral gene transfer.
Through evolution, grasses adapted to capitalize other plants’ genetic secrets so they could grow bigger, faster, stronger and adapt more readily.
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“We now know that it is a widespread process in grasses,” said Luke Dunning, research fellow in the School of Biosciences and senior author of the research. “We have even found gene transfers in crop genomes such as (corn) and wheat. This study is the first where we are able to calculate how frequently these transfers happen and something that is essential to know how important it is for a plant’s evolution.”
The phenomenon was documented in an earlier paper of Dunning’s team published in 2021. His team had scanned the genomes of 17 grass species and found evidence for transfers in 13 of them including corn, sorghum, switchgrass, teff and wheat.
“We then looked (to see) if it was more common in plants with a particular trait (e.g., annual versus perennial) but there was only a weak signal of transfers being more common in species that have rhizomes and can asexually reproduce. Initially, this made us think that transfers were happening through the roots, but we now think this is a red herring (as) we detected transfers in numerous species without rhizomes. We now think it involves reproductive contamination.”
He said that, through reproductive contamination, there would be normal fertilization between two individual plants of the same species with a small amount of DNA from a third individual included.
“In fact, we think this likely mirrors some methods used to make GM crops,” said Dunning. “To make a GM crop, there are many different methods. Some require more human intervention and can only happen in the lab. Others require almost no human intervention and could occur in nature.
Some of these, such as ‘repeated pollination’ are as simple as applying pollen from the same species and a different species in a specific order at a specific time. (That method) has been used to make GM grasses in the lab. This process could be easily mirrored in the wild where pollen from one species lands on the stigma of another. It may be happening all the time.”
Natural gene spread is an occurrence enhanced by the wind. He said if a crop grows in a monoculture, it is less likely to have the opportunity to acquire genes from another species.
In the current study, they worked on a tropical wild grass called Alloteropsis semialata, also known as black seed grass or cockatoo grass, and studied populations that grew in more species-rich areas of Zambia. They had more natural transfers than grasses growing in less diverse grassland areas in parts of South Africa.
The team sequenced multiple genomes of the grass at different points in its evolution to find how many genes were acquired and how often.
“In total, we detected 168 laterally acquired genes and these were accumulating at roughly one transfer every 35,000 years,” he said. “This doesn’t sound often but it can still have a profound effect on a species’ evolution. Also, a majority of the genes we detect are shared among different geographic locations, meaning they have been retained, probably because they are advantageous. We miss a lot of the insertions that have no, or even negative, effects. So, in reality, it might be that this process is much more common. But every 35,000 years, one (lateral transfer) sticks.”
Of importance, he said, is that a lot of the genes have functions associated with disease resistance, stress tolerance, and energy production.
The lateral gene between different species within the grass family would be akin to genes moving between, for instance, maize and rice, Dunning said.
“As long as they co-occur, they seem to be able to pass genes,” he said. “One of the cool patterns we see is crops like (corn) contain genes from a Mexican crop weed. This makes perfect sense as (corn) was domesticated in Mexico.”
Given the environmental stresses plants are experiencing with climate change, the ability to benefit from lateral gene transfer could be a saving grace for many grass species.
“It’s hard to tell,” he said. “But evolution is often an arms race. This process definitely allows grasses to take an evolutionary shortcut to adapt quicker. But we don’t know how common this process is in other species. Given our ideas around the mechanism, I wouldn’t be surprised if it was equally common in other wind-pollinated species.”
The reality of lateral gene transfer and its evolutionary benefits over time is bound to raise questions about contemporary genetic modification and the deliberate movement of genes between plant species.
“Our work shows that genes can move between species and moving genes between species is the goal of making GM crops,” he said. “So, the end result is the same and even the mechanism might be the same. We also know that these gene transfers occur in the crops we eat so they are naturally GM already.”
He said he is unsure how this study will affect the GM debate.
“If you support GM crops, you will see this as evidence that it’s a natural process. If you are anti-GM, you may see this as evidence that genes inserted into crops can escape to other species and not just closely related wild relatives. If we understand how this happens in the wild, potentially we can control this risk.”
The study will be of particular benefit to crop farmers and breeders, but Dunning feels a big benefit might be the study’s influence on how people understand the GM process and its closer connection to natural influences.
Research is continuing and one of the main objectives is to recreate some of the documented natural transfers using the GM “reproductive contamination” methods to support their hypothesis.
“We want to see if we can detect transfers in thousands of seeds collected from the wild, which might give us the true rate of natural gene transfer,” he said. “Most of our work in crops has focused on a single variety. We are expanding our work in (corn) and sorghum to see if different varieties have different laterally acquired genes. It would be fascinating if some of these are linked to agronomic traits.”
The research was published in the journal New Phytologist.
