This research shows that nitric oxide (NO) acts like a chemical messenger that helps mushroom fungi grow and reproduce when oxygen is scarce. Scientists studied a fungus found deep below the ocean floor and discovered that NO helps the fungus extend its root-like structures, germinate spores, and even initiate the formation of fruiting bodies (the mushroom stage). When they blocked NO with chemicals, growth slowed down, but when they added extra NO, growth accelerated. This discovery could help us understand how fungi survive in extreme environments with little oxygen.