Bacterial genes drove evolution of land plants

Bacterial genes drove evolution of land plants

The green alga Micrasterias is closely related to land plants. © tonaquatic/ iStock

Hundreds of genes in today’s plants originally come from bacteria, fungi and viruses. This is shown by a new study that examined the genomes of 31 plants for traces of horizontal gene transfer, i.e. for the transfer of genes independent of species boundaries and reproduction. Many of the genes that plants received from other organisms now perform important biological functions. Among other things, they help terrestrial plants to adapt to drought and absorb nitrogen from the soil.

For bacteria, horizontal gene transfer plays a major role when it comes to quickly adapting to new circumstances. Unlike vertical gene transfer, where genes are passed from parents to offspring during reproduction, horizontal gene transfer (HGT) transfers genetic material directly from one individual to another. In this way, antibiotic resistance, for example, can spread rapidly. The extent to which the HGT also plays a role in higher, multicellular organisms such as plants and animals has been a matter of debate up until now.

genes from microbes

A team led by Jianchao Ma from Henan University in China has now examined the genomes of 31 plants for traces of horizontal gene transfer. Plants analyzed included mosses, ferns, grasses, trees and charophytes, a group of green algae related to modern land plants. The result: “Our data suggest that HGT occurs in charophytes and all major groups of land plants,” the researchers write.

According to the analysis, almost 600 gene families in modern plants have their origins in other organisms. “Most of the acquired genes come from bacteria. However, a considerable part is also due to fungi,” explain Ma and his colleagues. In green algae in particular, they also discovered several families of genes that were apparently transferred from viruses to the ancestors of the plants examined. Some gene sequences could even have migrated from aquatic animals to green algae. “Whether the similarity of the gene sequences between plants and aquatic animals is actually due to a gene exchange between the organisms needs to be investigated further,” say the researchers.

Did gene transfer help with going ashore?

Using the genome comparisons, the researchers identified two major episodes of horizontal gene transfer during the evolution of land plants. 177 gene families were transferred from microbes to plants during the first episode, 107 during the second episode. In the course of evolution, they apparently gave the plants useful properties and were preserved over millions of years – not only in primitive plants such as green algae and mosses, but also in seed plants. “Around 58 percent of the genes from the first episode and 71 percent of the genes from the second episode are still found in today’s seed plants,” the researchers said.

“Our results suggest that HGT plays an important role in the evolution of land plants,” says Ma’s colleague Jinling Huang. Compared to mutations from vertical gene transfer, HGT allows plants to quickly acquire new traits. Some of these new traits may have helped plants adapt to a drastically changed environment, such as the transition from water to land. “I suspected that horizontal gene transfer helped plants colonize the land, but we didn’t realize how important it was until now,” Huang said. “Our study changes the conventional view of the evolution of land plants.”

Genes with useful properties

Genes acquired include those that give plants some drought resistance, help them ward off pests, and are involved in taking nutrients from the soil and transporting them to their cells. Genes originally from bacteria also play an important role in the synthesis of auxin, one of the most important growth hormones in plants. In future studies, the researchers want to examine the function of some of the acquired genes in more detail. It is conceivable that genes that are responsible for desirable properties could be specifically transferred to crops in the future.

Source: Jianchao Ma (Henan University, China) et al., Molecular Plant, doi: 10.1016/j.molp.2022.02.001

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