Viruses are deceptive little buggers, mutating often to dodge their hosts’ immune defenses. Plants fight back using a weapon called RNA interference (RNAi), which rips apart the viral machinery. Now, a new study shows that fruit flies employ the same defense–the first example of animals using this antiviral strategy. According to a related study, the genes behind this resistance are evolving rapidly to keep up with an ever-changing adversary.
For most creatures, RNA is just the middle man that helps a gene make a protein. But many viruses can get by on RNA alone. When they invade a cell, their RNA infiltrates the host’s genetic machinery, tricking it into making viral proteins. Scientists knew that all cells can shred unwanted RNA using RNAi, but they had never observed living animals using this strategy to defend against viruses.