Plants have epigenetic memory, that is, a type of memory that is transmitted from parents to children through the DNA of germ cells . It would be, for us to understand each other, an inheritable memory. Epigenetic memory helps plants to remember how cold it was in winter, not to bloom at that time, but in spring.
This memory is produced through modifications that occur in proteins called histones, around which DNA is wrapped. One of these modifications, named H3K27me3 , tends to mark genes that are turned off. In the case of flowering, cold conditions cause H3K27me3 to accumulate in the genes that control flowering.
Previous experiments led by Frédéric Berger, from the Gregor Mendel Institute of the Austrian Academy of Sciences, demonstrated how H3K27me3 is transmitted from cell to cell so that, in spring, plants remember that it was cold and that winter is over, allowing them to bloom in the right moment. As soon as the plants give seeds, this information is erased from memory so that they do not bloom too soon when the following winter arrives .
But how is the memory erasure process? An international team of researchers led by Frédéric Berger wanted to answer exactly this question. What they found was that once the plant produces seeds, the H3K27me3 modification disappears from the sperm . This is so because the sperm of the plant have a histone incapable of transporting the aforementioned modification. In this way, the modification that makes the plant remember when to flower disappears from hundreds of genes, not only those that prevent flowering, but also those that control important functions in seeds. This phenomenon is known as epigenetic resetting and is similar to erasing and formatting data on a hard drive.
“This makes a lot of sense from an ecological perspective,” said Dr. Borg, first author of the paper collecting the research and findings and recently published in Nature Cell Biology . “Since pollen can spread over great distances, for example due to the wind or bees, and that much of the “memory” carried by H3K27me3 is related to environmental adaptation, it makes sense that the seeds “forget” the environment of their father and instead remember that of their mother, since most likely to spread and grow alongside the mother . “
“Like plants, animals also erase this epigenetic memory in sperm, but they do so by replacing histones with a completely different protein. This is one of the first examples of how a specialized variant of histones can help reprogram and readjust a single epigenetic mark, leaving others intact. There are many more unstudied histone variants, both in plants and animals, and we hope that the aspects of this readjustment mechanism that we have discovered will be found in other organisms and developmental contexts, “said Jörg Becker, a researcher at the Gulbenkian Institute of Science who was also involved in the study.
Referencia: Borg, M., Jacob, Y., Susaki, D. et al. Targeted reprogramming of H3K27me3 resets epigenetic memory in plant paternal chromatin. Nat Cell Biol (2020). https://doi.org/10.1038/s41556-020-0515-y
