New plant DNA research suggests that mutations are non-random

Grey Monroe, who is currently an assistant professor in the Department of Plant Sciences at UC Davis and principal investigator at the Monroe Lab, was a postdoctoral student in Germany at the Max Planck Institute when he made a surprising discovery — one that led to three years of plant genome research.

“You’ve probably heard in biology class at some point that mutations are random,” Monroe said. “What we found is that the places that have very low mutation rates are actually the places in the genome that are responsible for the most important biological functions of the plant.”

Researchers spent three years sequencing the DNA of hundreds of Arabidopsis thaliana, or thale cress. Monroe said that this commonly-studied plant is the “fruit fly of plant research” due to its relatively small genome. 

The researchers grew specimens in a lab environment, “which allowed plants with defects that may not have survived in nature [to] be able to survive in a controlled space.” When the genomes were then sequenced, analysis of the mutations revealed a non-random pattern. Detlef Weigel, the scientific director at Max Planck Institute and senior author on the study, talked about what “random” means when it comes to mutations. 

“What is generally accepted is that mutations are random with respect to being ‘good,’ ‘bad’ or ‘neutral,’” Weigel said. “We assume that’s random, and then natural selection produces that pattern that we see. But this showed that instead, there are fewer mutations to begin with in those really important genes.”

However, even after seeing a pattern of non-random mutation, explanations other than mutation bias remained. “How do you know you’re not just accidentally observing natural selection?” Monroe said. “Because we would expect natural selection to remove that bias anyway. So without getting into the weeds too much, no pun intended, we spent a lot of time doing analyses that were able to show that that was not what was going on.” 

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