How horizontal gene transfer changes evolutionary theory

Ferris Jabr in Aeon:

ScreenHunter_913 Dec. 17 16.11Between 300 and 130 million years ago, as trees and flowering plants grew to dominate the globe, the sun-loving ferns of yore found themselves trapped beneath forest canopies. Most fern species perished under this umbrage, but the ones that survived learned to live on lean light. These persistent plants evolved a molecule called neochrome that could detect both red and blue light, helping them stretch towards any beams that managed to filter through the dense awning of leaves.

Neochrome’s origins have long eluded scientists. As far as anyone knew, the gene that codes for neochrome existed in only two types of plants separated by hundreds of millions of years of evolution: ferns and algae. It was extremely unlikely that the gene had been passed down from a common ancestor, yet somehow skipped over every plant lineage between algae and ferns. About two years ago, while searching through a new massive database of sequenced plant genomes, Li found a near-exact match for the neochrome gene in a group of plants not previously known to possess the light-sensitive protein: hornworts. Through subsequent DNA analysis of living specimens – like those he collected in Florida – Li confirmed his suspicion: ferns did not evolve neochrome on their own; rather, they took the gene from hornworts.

More here.