The construction of a flower is quite fascinating: the four very different types of organs that make up the flower emerge from the same microscopic structure composed of stem cells that were initially identical. The differentiation of these cells is controlled by epigenetic marks that are affixed to its DNA. These marks regulate the reading of specific genes that will allow the development of a petal, a sepal, a pistil or a stamen! But how are these marks orchestrated?

There are "permissive" marks that give access to the genes, while other marks are "repressive". In animals, the canonical models for orchestrating these antagonistic markers favor their simultaneous presence on developmental genes in embryonic stem cells. The reading of these genes for differentiation is initiated when the repressive mark leaves. Researchers at the BIG have now shown that this is not always the case, especially in plants. Indeed, a monitoring across the entire genome of the plant Arabidopsis thaliana shows that the permissive mark could set the tone by initiating gene reading and differentiation. For its part, the repressive mark appears to be less directive: it changes later on, during the course of cellular divisions and differentiations.