Phycomyces fruiting bodies with spore-containing spheres at their tips. Inset: An OCTIN crystal, 5 microns acrossTU ANH NGUYENWhen food runs low, the pin mold fungus, Phycomyces blakesleeanus, sends out spindly fruiting bodies topped with spores. The fungus grows in dung, and needs to figure out which way is up to spread its spores and reproduce. The trick it evolved is to sense gravity using large protein crystals that fall to the bottom of cell vacuoles. Just how the fungus acquired this ability was a mystery, but new research published in PLOS Biology today (April 24) shows that it originated in bacteria, which, curiously, can’t form these large crystals.
The genetic gift that encodes the crystals is an unusual case of what’s known as horizontal gene transfer (HGT), an exchange of DNA between organisms, says Sara Branco, a mycologist at Montana State University who was not involved in the study. Typically, HGT provides an immediate gain of function to the recipient—like swapping antibiotic resistant genes among bacteria—but this gene doesn’t have any known function related to gravitropism in bacteria. The result shows “that [HGT] is just another way to get raw material for evolution,” she says.
It kind of flips upside down our general perception of why horizontal gene transfer is happening.—Jason Slot,
Ohio State University
Earlier work by scientists discovered the Phycomyces solution for sensing gravity in 1999, but the evolutionary origin of ...
