Bad news, folks. That plant you shoved in a corner and neglected to water for three weeks hasn't forgotten it. In fact, that plant has a memory and is probably simmering with all sorts of grievances.
A little primer on prions. They start as normal proteins, just like all the others that exist in our bodies, but they do have one special ability: They can spontaneously change into an abnormal shape — and thus become prions. When a prion comes in contact with a normal prion protein, the protein version then transforms into another full-fledged prion. And the sequence continues. This can lead to degenerative diseases, like mad cow disease (bovine spongiform encephalopathy). Researchers still aren't certain about the role of normal prion proteins, in general, but speculate they help neurons communicate.
On the plus side, prions also have been shown to pass down beneficial traits in yeast, which leads to evolutionary changes that help survival. So researchers set out to see if plants might also contain prions (or prion-like proteins).
They found that when they inserted proteins from the plant Arabidopsis thaliana (thale cress) into yeast, one of the proteins had prion-like traits. The proteins took on the abnormal shape and spread that shape to the proteins around it — and continued to do so for further generations. They were self-perpetuating.
Why would having prions benefit plants? It's too early to say for sure. But plants would benefit from having an inherited memory of, say, temperature. Keeping track of how much cold or warm weather has passed might allow the plant to flower at the right time, for instance.
So while we know prions are found in humans and yeast, more research must be done to confirm their presence in plants. In the meantime, best to be on the safe side and kindly water that ficus.