Around 500 million years ago, aquatic plants migrated from water to land, and they may have been able to do it with genes adopted from bacteria, fungi and viruses.
鈥淭he movement of green plants from water to land represents a major habitat transition, and plants have been intimately associated with bacteria and fungi,鈥� says at East Carolina University in Greenville, North Carolina.
This physical proximity is key, because it could allow a process called horizontal gene transfer (HGT), in which organisms gain genes from another species. This may have given early plants traits that made life on land possible, as the acquired genes may allow the recipient to adapt to new habitats or exploit new resources.
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Previous research by other groups already hinted at genes hopping from and into early land plants.
Huang and his team analysed genomic data, the full set of genetic instructions, for 31 species representing the primary plant groups 鈥� mosses, ferns, seed plants and so on 鈥� and charophytes, the algaes mostly closely related to plants. They carefully screened the data for genes acquired from other organisms and then built family trees to determine the evolutionary history and the direction of transfer.
The researchers found that 593 families of genes in these plants originated in a mix of fungi, bacteria and viruses.
Many of the acquired genes had roles in biological processes key to living on land. For instance, the LEA2 gene family is involved in desiccation resistance. The pectin esterase gene families have a role in the development of cell walls, which lend important structural support for upright growth in land plants. Both LEA2 and pectin esterase gene families came from bacteria. An ammonia transporter gene family important for the uptake of nitrogen from soil came from fungi.
The sheer scale of the gene transfers is surprising, says at the University of Bristol, UK.
HGT is widely reported in single-celled life. But its role in multicellular organisms has been controversial, says Paps, who wasn鈥檛 involved in the research. 鈥淸HGT] played a much larger role in the evolution of plants than what we suspected before.鈥�
The timing of more than 280 of the gene family transfers cluster into two major evolutionary events: the origins of charophyte algae and plants鈥� first colonisation of land.
Paps鈥檚 own work has associated these events with substantial spikes in new types of plant genes. 鈥淭his correlates perfectly,鈥� he says. 鈥淚n those two specific episodes of the history of plants, there were explosions of genomic novelty.鈥�
It isn鈥檛 known precisely how the HGT occurred, but the reproductive structures of mosses and aquatic algae are more exposed to the elements than later plants with more protected structures, says at Cornell University in New York. This might increase the chance that close interactions with microbes result in a gene transfer in sex cells that can be passed onto the next generation.
Molecular Plant
