DNA methylation is one of several epigenetic mechanisms important for controlling gene expression in eukaryotes.
Arabidopsis. Image credit: Carl Davies, CSIRO/CC BY 3.0.
DNA methylation is a normal biological process in living cells in which small chemical groups called methyl groups are added to DNA.
This activity controls which genes are turned on or off, which affects a variety of characteristics, including how the organism responds to its environment.
Part of this job involves silencing, or turning off, certain pieces of DNA moving around in an organism’s genome.
These so-called jumping genes, or transposons, can cause damage if left unregulated.
This entire process is controlled by enzymes, but mammals and plants have developed different enzymes to add methyl groups.
“Mammals only have two major enzymes that add methyl groups in one DNA context, whereas plants actually have multiple enzymes that do it in three DNA contexts.” said researcher Professor Xuehua Zhong. Washington University in St. Louis.
“This is the focus of our research. The question is: why do plants need extra methyltransferases?”
“A particular gene or combination of genes contributes to a particular characteristic or trait.”
“If we know exactly how they are regulated, we can find ways to innovate techniques for crop improvement.”
Professor Zhong and his colleagues focused on two enzymes specifically found in plants: CMT3 and CMT2.
Both enzymes are responsible for adding methyl groups to DNA, but CMT3 specializes in one part of DNA called CHG sequences, and CMT2 specializes in another part called CHH sequences.
Despite their functional differences, both enzymes are part of the same chromomethylase (CMT) family and have evolved through duplication events that provide plants with additional copies of genetic information.
We use a common model plant called Thale cress (Arabidopsis), the study authors investigated how these duplicated enzymes evolved different functions over time.
They found that somewhere along the evolutionary timeline, CMT2 lost the ability to methylate CHG sequences. This is because it lacks an important amino acid called arginine.
“Arginine is special because it has an electric charge,” says Jia Gwee, a graduate student at Washington University in St. Louis.
“Because it is positively charged inside cells, it can form hydrogen bonds and other chemical interactions with negatively charged DNA, for example.”
“However, CMT2 contains a different amino acid, valine. Valine is uncharged and therefore cannot recognize CHG contexts like CMT3. We think that is the reason for the difference between the two enzymes. Masu.”
To confirm this evolutionary change, the researchers used a mutation to move arginine back into CMT2.
As expected, CMT2 was able to methylate both CHG and CHH. This suggests that CMT2 is originally a duplicate of CMT3, a backup system to offload as DNA becomes more complex.
“But instead of just copying the original functionality, we developed something new,” Professor Zhong said.
This study also provided insight into the unique structure of CMT2.
This enzyme has a long, flexible N-terminus that controls the stability of its protein.
“This is one of the ways plants have evolved to increase genome stability and combat environmental stress,” Professor Zhong said.
“This feature may explain why CMT2 has evolved in plants growing in very diverse conditions around the world.”
of result Published in today’s diary scientific progress.
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Gwee Others. 2024. scientific progressin press. doi: 10.1126/sciadv.adr2222
Source: www.sci.news
