The genetic program at the root of the biological stock exchange.

Beneath the gardens, farmlands and forest floors that surround us, a hidden world blooms in careful cooperation and intense competition. The mutualistic symbiosis of the thread-like hyphae of fungi and plant roots (collectively termed mycorrhizae from the Greek mýkēs - meaning 'fungus', and rhiza - for 'root') is present in the vast majority of plant species. As with most intimate relationships, this symbiosis functions on a principle of 'give and take'. As an autotroph, the plant is able to synthesize all the sugars it requires through photosynthesis; however, its immobility hinders its capacity to forage for nutrients vital for its growth and survival. With an expansive network of hyphae, the heterotrophic fungus is able to locate and remobilize water and nutrients, such as phosphorus (P) and nitrogen (N), and barter them for precious sugars with the plant. An article in this issue of Physiologia Plantarum (Zhao et al. 2019) describes alterations in the genetic programming that takes place in the plant root upon the establishment of this fascinating relationship, which has profound implications for plant productivity and soil management methods.