Sheffield scientists unlock the secrets of plant memory

A study published in Nature Communications, led by Professor Jurriaan Ton and Dr Adam Hannan Parker at the University of Sheffield, has identified mechanisms of how 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 specialised immune cells found in animals, but they still learn from experience. Once a plant survives an infection, it preps its defence system to launch a quicker, stronger response when a pathogen attacks again. Research from the Ton lab 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. 

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 centres of chromosomes.” Dr Adam Hannan Parker

The team discovered that plants can store immune memories without compromising their overall DNA stability. Following ROS1-triggered vaccination, the plant temporarily redirects its DNA-silencing machinery away from defense genes and toward the transposon-rich chromosome core, locking down these jumping genes. This keeps the genome secure while leaving defence genes in the chromosome arms free to retain their epigenetic memory.

Professor Jurriaan Ton says “Conventional crop breeding mainly selects for differences in DNA sequence. By changing the distribution of DNA methylation, the tool could instead generate epigenetic variation that alters how existing genes are regulated. Our collaboration with researchers at the Okinawa Institute of Science and Technology (OIST) in Japan is revealing promising results in rice, suggesting the epigenetic memory by XVE:ROS1 in rice is not completely reset between generations, with part of it transmitted to offspring.” 

The Sheffield team is now refining the ROS1 vaccination tool to deliver a more powerful “epigenetic shock” aiming to obtain variation that remains stable across generations. Breeders could then screen these plants for beneficial traits. 

“Potential targets go beyond disease resistance alone and could include tolerance to abiotic stresses, such as drought, heat or salinity. The approach could also help generate variation in other complex quality traits, including the nutritional value of vegetable crops and compounds with potential health benefits.” 

Although further research is needed, this work opens an entirely new  route towards epigenetic crop breeding: expanding the variation available to breeders by changing how genes are controlled.