​Researchers at CEA, CNRS and Université d’Aix-Marseille have investigated a signaling pathway, scarcely studied until now, which was already present in the bacterial ancestor of chloroplast, the compartment where photosynthesis takes place. This signaling pathway is dependent on a molecule that plays an important role in bacterial stress response: Guanosine tetraphosphate. By genetically modifying the guanosine tetraphosphate content in plant chloroplast, the researchers have shown that it inhibits chloroplast activity, impacting both function and size. Surprisingly, the researchers have also shown that this bacterial signaling pathway plays a key role in communication between the chloroplast and the cell nucleus that regulates plant growth and development.

This signaling pathway could be used to optimize the photosynthetic efficiency of plants subject to water and nutrient deficiencies, with potential applications in agriculture and reactor-based crop development for green chemistry and algae-based biofuel solutions.

Photosynthesis takes place in chloroplast, which arose from an endosymbiotic relationship between a unicellular eukaryote organism [1](common ancestor of plants and animals) and a bacterium over a billion years ago. This relationship enables photosynthetic eukaryotes (green plants and algae) to support ecosystems throughout the planet.