The DNA mutations that drive evolution are generally thought to be fairly random, but a new study suggests there’s some order to the chaos. Comparing the genomes of hundreds of plants grown in a lab, a team of scientists has found that mutations are far less likely to occur in genes essential for survival.
Chance plays a big part in evolution. Conventional thinking goes that DNA mutations will randomly arise in an organism’s genome, and if these new traits happen to help the organism survive and reproduce, then those mutations will be passed down to the next generation. Over a long enough period, the traits can become characteristic of a population or species.
But is there a pattern to where in the genome DNA mutations occur? To investigate, researchers from UC Davis and the Max Planck Institute grew hundreds of thale cress plants in the lab, then sequenced their genomes and compared where DNA mutations had taken place – and a non-random pattern seemed to emerge.
“We always thought of mutation as basically random across the genome,” says Grey Monroe, lead author of the study. “It turns out that mutation is very non-random and it’s non-random in a way that benefits the plant. It’s a totally new way of thinking about mutation.”
By growing the plants under controlled lab conditions, the team sought to remove the non-random influence of natural selection, ensuring that plants that normally wouldn’t survive in the real world wouldn’t be weeded out by any negative mutations.
Within the hundreds of plant genomes, the team identified over a million mutations, which seemed to be concentrated in certain parts of the genome. That left patches with consistently low mutation rates, as low as one third of those in other regions. When the scientists checked which genes were located in those patches, they found an abundance of essential genes, including those involved in cell growth and gene expression.
“These are the really important regions of the genome,” says Monroe. “The areas that are the most biologically important are the ones being protected from mutation.”
Intriguingly, these areas also seemed to have stronger DNA-damage-repair mechanisms, indicating a kind of reinforcement method to ensure these crucial sequences remain functional.
“The plant has evolved a way to protect its most important places from mutation,” says Detlef Weigel, senior author of the study. “This is exciting because we could even use these discoveries to think about how to protect human genes from mutation.”
The new research adds to a growing body of work that deepens our understanding of the role of DNA mutations in evolution. A 2014 study found that mutations occur more frequently near repeated sequences, while another from 2019 identified mutation hotspots in recombination sites, where the chromosomes from each parent pair up.
The researchers on the new study say that this work could eventually lead to improvements in engineering better crops, and even controlling human diseases caused by DNA mutations, such as some types of cancer. But any applications in these areas are no doubt a long way off.
The research was published in the journal Nature.
Source: UC Davis
