The evolution of life on land is commonly depicted as a fish that grows rudimentary limbs and crawls onto a beach. But the true terrestrial pioneers were bacteria and fungi—and some of these microbes lent a helping hand to an ancestor of plants and some algae, researchers reported yesterday (November 14) in Cell. The finding provides support for the controversial idea that bacteria can transfer genes not just amongst themselves, but also to more complex species.
“That horizontal gene transfer may have contributed to the colonization of land is pretty exciting,” Pamela Soltis, a plant evolutionary biologist at the University of Florida in Gainesville who was not involved in the work, tells Science.
In the study, researchers led by Michael Melkonian of the University of Duisburg-Essen in Germany and Gane Ka-Shu Wong of the University of Alberta in Canada sequenced the genomes of two algal species of the class Zygnematophyceae that live in damp places on land and are thought to be close relatives of plants. The researchers then compared the two, Spirogloea muscicola and Mesotaenium endlicherianum, to plants and other alga, and identified 902 genes that were shared by S. muscicola, M. endlicherianum, and the plants, but not with water-dwelling algae.
Expanding their search, the researchers also found the shared genes in soil bacteria, but in no other lifeforms. They suggest that the genes hopped from soil microbes into a common ancestor of plants and the two Zygnematophyceae species. The genes are involved in processes that presumably helped the ancestor—and now, modern plants and some algae—cope with droughts and other conditions they encounter on land. “I am very convinced that the two gene families described in the paper were acquired from bacteria,” Jinling Huang, a plant biologist at East Carolina University in North Carolina who was not involved in the study, tells Science.
Melkonian tells The New York Times that it’s clear plants built on the innovations of other organisms to colonize land. “The surface of the planet was green [with life] hundreds of millions of years before the first land plants,” he says.