To determine the origin of this crystal matrix, Dr. Jedd and his team isolated the proteins that built them, homed in on one called OCTIN and traced it to a single gene. By looking for related organisms throughout evolutionary history with similar proteins, his team determined that a common pin mold ancestor likely acquired the gene from a bacterium that shared the same soil hundreds of millions of years ago.
This happened randomly, through a process called horizontal gene transfer. It allows an organism to “pick up a piece of DNA from a completely unrelated species and potentially use it for adaptive purposes,” Dr. Jedd said. If the adaptation aids survival, the organism passes it on to future generations.
How this happened in the exchange between ancient fungus and bacteria was unusual. In the bacteria, the gene couldn’t have produced a gravity sensor because the protein structures it made were too small. But the researchers showed that the proteins were capable of self assembling. Following additional mutations inside the fungus, that ability may have resulted in the crystal matrices that now help it know up from down.
“Those little nanostructures could cluster together, and in that way they could attain a size that could make them primitive or rudimentary gravity sensors,” he said.
Instead of creating a shared trait, the gene, with a few mutations, had created a novel one.
Dr. Jedd said understanding OCTIN and other self-assembling proteins could help with developing drugs that could know exactly where and when to dissolve in the body.
But there’s another potential application: When your housemates hound you for being a fridge slob, try telling them you’re observing gravitropism at work. Maybe it will charm them.