The emergence of seed-producing plants over 300 million years ago was an evolutionary watershed, opening up new environments for plants that would eventually light our world and supply much of our food. Connected to flowering plants. But, as the newly released DNA sequence suggests, it wasn’t as dramatic as it sounds.

The genomes of three species of ferns and one of the oldest seed-bearing plants, the cycad, share the same gene for the sporulation mechanism of ferns that appeared tens of millions of years ago. is shown. They apparently existed in a common ancestor, but were recruited for different reproductive functions as plants diverged.

The fern and cycad genomes, published in a series of papers over the past few months, “close a gap in gene flow during plant evolution,” said Shu-Nong Bai, an emeritus plant developmental biologist at Peking University. say. Genus Ginkgo biloba. “Evolutionary Innovation [can] It is brought about by alternatively using existing genes and networks rather than new genes. The genome also teaches us a second striking lesson. That is, plants acquired some of their genes not through mutation or selection, but directly from fungi and other microorganisms through a controversial process called horizontal gene transfer.

Since most fern genomes are so large and focused on crops such as rice, wheat and maize, the majority of the over 800 plant genomes sequenced so far are derived from seed plants. . So far, only two have come from ferns with unusually small genomes. As a result, “we only had a small snapshot of plant evolution,” says Blaine Merchant, a plant evolutionary geneticist at Stanford University.

Thanks to advances in long DNA sequencing and reduced costs, his team and three other groups are now able to test ferns with more typical, large genomes and non-flowering plants with bare seeds, such as pines and pines. I’ve been working on a certain cycad seed. other conifers. Jennifer Wisecaver, an evolutionary biologist at Purdue University, said:

Fern genomes, each with about 30,000 genes, reveal the majority of genes previously associated with flowering plants that evolved more than 200 million years later. For example, Marchant and his colleagues reported on his September 1st. natural plant That aquatic fern, Ceratopteris Ricardithere are 10 members of a gene family known to control flowering time, seed germination and flower shape in small flowering plants, Arabidopsis thalianaTheir role in ferns is unknown, but seven of these genes are activated in leaves where spores are produced, suggesting that they play a role in the reproduction of ferns and seed plants.

Jianbin Yan, a plant physiologist at the Institute of Agricultural Genomics at the Chinese Academy of Agricultural Sciences, and colleagues found similar similarities in Ginkgo biloba. Adiantum capillus-venerisIts DNA contains genes for transcription factors called EMS1 and TPD1. These are proteins that regulate genes involved in pollen development in maize and other seed plants. natural plantThese pollen gene regulators are activated in the virgin sporangia, the tissue in which the spores develop.

Hongzhi Kong, a plant evolutionary and developmental biologist at the Institute of Botany, Chinese Academy of Sciences, added that the fern’s genome also contains three genes that control seed development in flowering plants. According to Yan, ferns are “evolutionarily pivotal to our comprehensive understanding of seed origin and diversification.” The cycad genome contains similar networks, indicating that they were active in the earliest seed plants, said botanists at the Fairy Lake Botanical Garden in deep mountains who led the sequencing. One Shouzhou Zhang said:

A new genome sheds light on one reason such insights have been elusive. Ferns are “notorious for having huge genomes,” says Fay-Wei Li, a plant evolutionary biologist at Cornell University. Their genome size was explained because the researcher assumed a process called whole-genome replication, in which the complement of an organism’s DNA doubles during replication. But, says Paul Wolfe, a plant geneticist at the University of Alabama in Huntsville, “the genomic footprint doesn’t double as we thought it would.” Instead, fern and cycad acquired most of his DNA from mobile DNA accumulations. This involves transposons and other genetic elements infecting the genome, propagating short sequences, or repetitive DNA, that are replicated over and over again.

The four new genomes are also changing the way we look at whether plants undergo horizontal gene transfer. Although microbes are known to constantly exchange genes to help them adapt to new conditions, it seems that multicellular organisms rarely borrow genes. It contains many bacterial and fungal genes. “It is remarkable that vascular plants have genes of bacterial and fungal origin,” says Kong.

For example, sequenced cycads have four copies of the fungal gene for a cytotoxin, a protein that can puncture foreign cells. ceratopteris There are 36 copies of another cytotoxic gene from bacteria in the genome. These acquired genes may have enhanced the new host’s defenses against pathogens and herbivores.

Botanist Verónica Di Stilio of the University of Washington in Seattle expects more surprises from the new genome. “Having a reference genome that is representative of each of the major plant lineages opens up so many possibilities,” she says. “The genome is a tool, it is the tip of the iceberg.”