Microbes transferred genes to ancient plants to help them evolve on land

The genes of microbes made the jump into green algae and plants hundreds of millions of years ago, suggesting the evolution of plants from water to land might have been driven by these events, according to a new study.

Researchers found almost 600 genes from bacteria, fungi and viruses that have been integrated into plants over time in a process known as horizontal gene transfer (HGT); many are the source of desirable traits for terrestrial life. The research was published in the journal Molecular Plant.

“Our study changes the conventional view on land-plant evolution,” says senior author Jinling Huang, professor in biology at East Carolina University in the US. “I have suspected that horizontal gene transfer helped plants to move from water to land, but we didn’t know how big a role it played until now.”

Horizontal gene transfer describes the movement of genetic material between organisms of different species – events which are common in bacteria and are responsible for the rapid spread of antibiotic resistance, for instance. However, its roles in complex multicellular organisms such as plants and animals remain controversial.

Traditionally, scientists thought that genes in plants and animals have only moved via vertical gene transfer, where genes are passed down from parents to offspring, and new genes and traits are achieved through mutations occurring. However, Huang and his colleagues found evidence from prior studies which made them think that HGT in plants might be more common than previously thought.

To investigate this, the team compiled the genomes of 31 plants, including species from all four plant groups – mosses, ferns, and trees which flower or produce cones and seeds, as well as charophytes, a group of green algae most closely related to modern land plants.

Using genome analysis to compare the complete genome sequences of different species, they looked for genes in plants which had originated from bacteria, viruses, fungi or animals, and found a total of 593 gene families.

This number is far greater than previously thought, and were transferred especially from microbes, such as bacteria and fungi. This research indicates that HGT is active in charophytes and all major groups of land plants, although interestingly more recently acquired genes are much less prevalent in seed plants. 

They also identified two major HGT events – during the early evolution of charophytes and the origin of land plants – when over a hundred gene families hopped over from microbes into plants. According to the researchers, these acquired genes may influence plant physiology and development, ultimately leading to better adaptation of plants to their environments and allowing them to live on land.

“Our finding suggests that HGT plays a significant role in land-plant evolution,” says Huang. “Compared with mutations from vertical gene transfer, HGT enables plants to gain new traits rapidly, and some of these new traits could help plants adapt to a drastically different environment, like when they moved from water to land.”

Many of these genes are known to perform important biological functions in plants. For example, the late embryogenesis abundant (LEA) genes, which come from bacteria, help plants adapt to a drier environment. The ammonium transporter gene, acquired from fungi, helps plants absorb nitrogen from soil for growth.

Next, the team plans to further explore the transferred genes in bryophytes, which is the plant group that includes mosses. Many foreign genes in these plants have unknown functions, and future research might help identify useful genes that can one day be transferred into crops to help augment them.

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