A study published in Nature Communications, led by professor Jurriaan Ton and Dr. Adam Hannan Parker at the University of Sheffield, has identified mechanisms by which plants maintain and reset stress memory from past infections. This immune memory enables plants to defend themselves more effectively against harmful bacteria and mildews, which are increasingly threatening our crop and food production.
Plants lack the specialized immune cells found in animals, but they still learn from experience. Once a plant survives an infection, it preps its defense system to launch a quicker, stronger response when a pathogen attacks again.
The research from the Ton lab had previously found that plants store this memory by removing chemical tags attached to their DNA that don't alter the underlying genetic sequence but influence the expression of the DNA. The enzyme REPRESSOR OF SILENCING 1 (ROS1) is responsible for the removal of these tags, effectively helping the plant retain a lasting memory of past threats: an epigenetic immune memory.
Keeping immune memory without destabilizing DNA
In this new study, the researchers have used a molecular tool, called XVE:ROS1, to switch on ROS1 activity in a far more controlled way than pathogen infection. This plant vaccination tool allowed them to investigate how plants establish immune memory, how long it persists and how it is subsequently erased.
"Too much ROS1 activity carries a potential risk. It can release silenced transposons, or 'jumping genes,' which move within the genome and cause mutations. These elements are particularly abundant in pericentromeres, the regions surrounding the constricted centers of chromosomes," Parker said.
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