During the early stages of their development, flowering plants will only turn green in the presence of light following a program known as photomorphogenesis. The cells of leaves then accumulate all of the proteins necessary for photosynthesis during the formation of mature chloroplasts, which are characterized by their green color. These chloroplasts are located within the cells, around the nucleus. Their development requires the expression of genes encoded in the nuclear DNA as well as in the chloroplast DNA. Many mysteries remain about the mechanisms (both molecular and genetic) that allow the expression of these two genomes to be coordinated. These mechanisms are nevertheless essential, as they allow the best possible use of the seed’s reserves according to how deeply the young seedling is immersed in the soil.
Researchers at the CEA-Irig have been investigating the role of the PAP8 gene, whose expression is regulated by light. By examining its regulation and function in vivo, they have shown that the PAP8 protein expressed by the gene is localized to the nucleus and the chloroplast, and has distinct roles in the two compartments.
The combined data indicate that a retrograde movement (relative to the signals sent by the chloroplasts towards the nucleus) of the PAP8 protein towards the nucleus could, together with other proteins, regulate the expression of nuclear genes according to the state of the plastids and their ability to produce the proteins of the photosynthetic apparatus, in a mechanism known since the late 1990s as genetic coupling.