Fairy Rings Share Magical Chemistry

For centuries, people around the world have been mystified by the formation of circles or arcs of accelerated plant growth in woodlands and grassy fields. The rings sometimes erupt with mushrooms, adding to the intrigue. Myth and superstition led these geometric patterns of plant growth to be called fairy rings. In 2010, a research team led by Hirokazu Kawagishi of Shizuoka University, in Japan, discovered that the “fairy” is the plant-growth regulator 2-azahypoxanthine (AHX), one of several purine-based natural products made by fungi. The researchers determined how AHX is produced from 5-aminoimidazole-4-carboxamide (AICA)—a compound in the purine metabolic pathway in animals, plants, and microorganisms—and began figuring out the complete biosynthesis pathway of the compounds in hopes of finding a practical use of the plant hormones in agriculture. Kawagishi’s team has now reported the discovery of an additional AHX metabolite, 2-aza-8-oxohypoxanthine (AOH), which is produced from AHX by the enzyme xanthine oxidase. And after detecting AHX and AOH in plants such as rice, the researchers have uncovered that the plants themselves actually biosynthesize the compounds (Angew. Chem. Int. Ed. 2014, DOI: 10.1002/anie.201308109). Kawagishi is now leading an effort to isolate key enzymes in the purine biosynthetic pathways as models for new agrochemicals or for engineering genetically modified plants.