The symbiotic trinity – the next step in evolution? EvoMoss

Endosymbiosis, the process where one organism engulfs another, was key for the evolution of life on Earth. One of the most significant examples is the origin of plants: a free-living cyanobacterium was engulfed by a host cell,  evolving into the chloroplast, the photosynthesising organelle in plants. Last year, a groundbreaking discovery identified another potential endosymbiosis: a free-living, nitrogen (N)-fixing cyanobacterium was engulfed by a marine alga, forming the marine nitroplast. This organelle supplies the host with newly fixed N, a key nutrient for all life. I propose that we are at the dawn of a terrestrial nitroplast in moss-cyanobacteria symbioses that can serve as a unique model system to unravel the evolution of a N-fixing organelle. Just as mitochondria and chloroplasts originated from ancient endosymbiotic events, the discovery of a terrestrial nitroplast would complete the “symbiotic trinity”, marking the third organelle acquired by plants.