Gene Pool

A. semialata grass in a Zambian savannah

Pascal-Antoine Christin

Some organisms develop genetic mutations by incorporating genetic material from unrelated individuals. This evolutionary shortcut, called lateral gene transfer, has been frequently found in single-celled organisms, such as bacteria, but scientists are just beginning to recognize its presence in multicellular organisms. Researchers have discovered evidence that distantly related grasses can swap genes.

An international team of geneticists, led by evolutionary plant biologist Luke T. Dunning of the University of Sheffield in the UK, sequenced the DNA of the grass Alloteropsis semialata, typically found in tropical areas of Africa, Asia, and Australia. A. semialata is the only plant whose variants use different kinds of photosynthesis, presenting a unique opportunity to study plant evolution. The grass’s African subspecies, like the majority of plants, uses C3 photosynthesis, while its other subspecies uses C4 photosynthesis, ideal for plants in drought-prone areas. Previous research found that the latter subspecies of A. semialata contained at least two genes that were from distantly related grasses. In this new in-depth analysis comparing over 22,000 A. semialata genes to those of nearly 150 other grass species, the researchers found a total of fifty-nine genes that appear to have come from at least nine other distantly related plants.

Some of those distant genes are used in photosynthesis, suggesting that they are crucial to the plant’s functioning and survival. “The acquired genes were already optimized for the C4 trait, and their acquisition therefore provided Alloteropsis with an evolutionary shortcut,” says Pascal-Antoine Christin, a plant biologist also at the University of Sheffield and senior author of the study. “Without the transfer, it would have needed to evolve the same mutations through sustained selection on new mutations.”

Exactly how these transfers occur is not yet known, but there are two leading theories. One is that genes are carried through pollen. “If the pollen from other species grew to reach an embryo of Alloteropsis that was already formed, some genes could move across adjacent cells,” says Christin. Another possibility is that gene transfer occurs underground among the grasses’ roots.

Understanding the mechanism will become crucial to evaluate how human-introduced genetic modifications might spread. While there are no documented cases of genetically modified crops passing on their genes to wild relatives, Christin says more research is needed to evaluate that risk. “Genetically modified crops are not as disconnected from natural processes as expected initially,” says Christin. But that’s just another dimension of what’s been happening in the wild long before human intervention. “One could almost say that genetically engineered grasses are natural.” (Proceedings of the National Academy of Sciences)