According to a new study conducted at the University of Oxford, a cellular mechanism termed DNA mismatch repair (MMR), preferentially protects plant genes from the damaging impacts of mutation.
Arabidopsis thaliana, the model plant species used in the study. Credit: Vasiliy Koval/ Shutterstock.com
While DNA sequence mutation is the key factor in species evolution, gene mutations are often harmful. In order to correct the DNA sequence after mutation, organisms have evolved repair mechanisms as a line of defense, of which DNA mismatch repair is one. The mutations that arise during the replication of the genome at the time of cell division are corrected by MMR.
The study, which was published in the journal Genome Research, is the first of its kind to suggest that MMR is targeted to specific regions of the genome, and preferentially repairs genes.
The team studied 9,000 mutations that were accumulated in five generations of a MMR-deficient strain of the model plant species---Arabidopsis thaliana. The results were then compared with mutations arising in an MMR-proficient strain.
The study is expected to have important implications for human health, especially in understanding the changes that happen in cells during tumor developments that underlie cancers.
MMR-deficiency causes cells to become tumorous, probably because such cells lack the gene protection that decreases the risk of mutation in the genes and usually suppresses tumor formation.
As expected, the mutation rate in the MMR-deficient strain was massively higher than in the MMR-proficient strain. But we were surprised to see that whilst mutations are more or less randomly spread throughout the genome of the MMR-deficient strain, they are not randomly spread throughout the genome of the MMR-proficient strain.”
Prof. Nicholas Harberd, University of Oxford
In the MMR-proficient strain, genes were identified to be preferentially protected from mutation, and not non-genic regions of the genome.
The findings indicate that rather than other regions of the genome, MMR preferentially repairs genes. This result significantly enhances our knowledge of the way in which organisms utilize MMR to reduce the rate of spontaneous mutation.
Prof. Harberd explained that even though genes are vital for the biology of organisms, the functions of the non-genic regions of the genome are not yet clear. According to him, natural selection might have helped the relative targeting of MMR to genes rather than non-genic regions.He added that the challenge lies in understanding how the targeting works.