Scientists at Cold Spring Harbor Laboratory (CSHL), including Professors Rob Martienssen and Leemor Joshua-Tor, have made significant strides in understanding how plants pass on epigenetic markers that regulate DNA activity, a process known as epigenetic inheritance. These markers play a crucial role in keeping certain genes inactive and are particularly common in plants. Understanding this process has potential implications for agriculture, food supplies, and the environment.
The researchers focused on transposons, also known as jumping genes, which can move around and disrupt other genes if activated. To prevent this, cells use a process called methylation to add regulatory marks to specific DNA sites, effectively silencing transposons. The team investigated the protein DDM1, which is necessary for this DNA methylation process in plants.
In plant cells, DNA is compacted by wrapping around histone proteins. However, this compact structure can block the access of enzymes responsible for methylation. DDM1 functions by sliding DNA along the histones, exposing regions that need methylation. This movement is comparable to a yo-yo gliding along a string, allowing histones to move along DNA without dislodging.
Through genetic experiments and cryo-electron microscopy, the researchers identified the specific histones that DDM1 displaces to remodel packaged DNA. They also discovered a histone found only in pollen that is resistant to DDM1 and acts as a placeholder during cell division. This histone retains the memory of its location during plant development, preserving epigenetic controls across generations.
These findings have potential implications beyond plants, as humans also rely on DDM1-like proteins for DNA methylation and genome integrity. Understanding how these proteins function could shed light on maintaining the functionality of human genomes.