How plants make friends with fungi

Many fungi damage or even kill plants. But there are also plant-friendly fungi: Most land plants live in close community with arbuscular mycorrhiza fungi (AM fungi) that stimulate their growth. Researchers have studied the development of this symbiosis and have identified a gene that is specifically activated by AM fungi and influences the development of the plant root: The GRAS transcription factor MIG1 stimulates growth of more and larger root cortex cells.
https://www.sciencedaily.com/releases/2016/10/161019100936.htm