Plants like Arabidoposis thaliana use a protein called decrease in DNA methylation 1 (DDM1) to methylate DNA to compact it, while human cells use a homologous protein. Loss of this protein in humans leads to a genetic syndrome, but A. thaliana plants that lacked DDM1 due to gene mutation continued to segregate chromosomes with no apparent impact on their phenotype. However, researchers previously found that these mutants activated a specific family of transposable elements (TEs) in their genome which produced short interfering RNAs that are involved in the RNA interference (RNAi) process that silence gene expression.
“We wondered whether this RNAi might be somehow making up the loss of centromere function,” said Rob Martienssen, a plant geneticist at Cold Spring Harbor Laboratory. In a study published in Nature Plants, Martienssen and his team showed that one family of TEs enriched in the centromere of chromosome 5 in A. thaliana produced short hairpin RNAs that were integral to the proper structure and function of that centromere.
In mutants that lacked DDM1 and RNAi machinery, the researchers found that chromosome 5 failed to segregate properly, causing infertility and other defects. They mapped the DNA region responsible for these effects to the centromere of chromosome 5 and determined that this region was enriched in their previously-identified TE family using long-read sequencing.
In the absence of DDM1 and RNAi, this TE doesn’t produce small RNAs, so the centromere is not methylated. These mutants also had few epigenetic tags on their histones, which contribute to the structure of the centromere.
When researchers supplied short RNA hairpins derived from this TE to the DDM1 and RNAi mutants, the hairpins promoted the proper epigenetic markers on the centromeric histones and reversed the chromosomal segregation defect.
By Shelby Bradford, PhD
Article can be accessed on: The Scientist