nai

Project Progress

Symbioses, the mutually beneficial relationships between two organisms, have evolved numerous times over the course of the evolutionary history of life on Earth. Different forms of symbiosis have resulted in some of the most profound evolutionary radiations; e.g., the origin of the mitochondrion from a symbiosis of a proteobacterium with early eukaryotes, the origin of the chloroplast from a symbiosis of a cyanobacterium with an originally heterotrophic eukaryote, resulting in the evolution of all photosynthetic lines of eukaryotes, and the establishment of multicellular photosynthetic organisms (plants) in terrestrial environments from a symbiosis of a fungus and a green alga.

We are characterizing the fungal symbiotic partners that may have been critical to the colonization of terrestrial environments on Earth by photosynthetic organisms. Using DNA extraction and amplification techniques, we have begun to identify the fungal lineages that currently play a central role in the widespread symbiosis between plants and fungi (mycorrhizal association). We have chosen to work with phylogenetically basal land plant lineages so that we can reconstruct the evolutionary history of this key symbiosis. During the last year, we have discovered a complex relationship between early lineages of multicellular land plants and their fungal partners. During part of the life cycle of ancient lineages of land plants, the fungal symbiotic partner appears to supply mineral nutrients to the host plant and in return, the fungus receives fixed carbon from the plant. During another component of the plant’s life cycle, the symbiosis involves an entirely different fungal partner and in this symbiosis, the plant is essentially a parasite on the fungus, receiving fixed carbon and mineral nutrients from the fungus. Thus, we are beginning to piece together a complex set of symbiotic relationships between early land plants and their fungal symbionts.