Ferns are weird — their genomes are messier than we thought: ScienceAlert

Ferns do have something special.

Their DNA is strange and complex. In fact, a fern — Hedyotis diffusa, or the tongue fern of the adder—holding the record for the multicellular organism with the most chromosomes. About 720 pairs of chromosomes can be found in most of its nuclei.

Well, it turns out our suspicions were right.

After years of painstaking work, scientists have finally sequenced the vast genomes of three different homosporous ferns, revealing that these harmful plants not only hoard DNA, but steal it from other organisms — and do so for millions of years.

“Each genome tells a different story,” said geneticist Doug Soltis of the Florida Museum of Natural History and co-author of one of the papers.

“Pteridophytes are close relatives of all seed plants, and they create a chemical deterrent to herbivores, which may be useful in agricultural research. However, until now, they remained the last major lineage of green life without a genome sequence.”

The genomes of these three ferns have been described in three separate papers.

A paper on the flying spider monkey tree fern (Cypress) in May natural plants. This week, a paper on the fern is added to the list (Clematis) and C-ferns (Horned Fern), which has been studied for decades as a model organism.

Soltis contributed to the C-fern paper as part of a team of scientists from 28 institutions around the world. Their effort was arduous, taking more than eight years to piece together the C-fern genome.

Results: One genome contained 7.46 GB of DNA in its 39 pairs of chromosomes, more than double the size of the human genome. It yielded some very interesting surprises, the researchers report.

In the past, scientists have attributed the large genomes and high chromosome numbers of ferns to repeated whole-genome duplications, in which the organism’s descendants accidentally inherit additional copies of the organism’s entire genome. This is common in plants and can bring benefits such as rapid evolution and differentiation.

However, organisms that experience this often experience brief adjustments in which most of the duplications are lost, resulting in a more normal genome. Unlike ferns.

“This has been a major discussion point for the past half-century and has led to all sorts of conflicting results,” said Stanford University botanist and co-author Daniel Brian Marchand.

“It’s very important to try to figure out the evolutionary process behind this paradox.”

the answer is C.richardiiIf replication is involved, the chromosomes of ferns are not the same DNA segments as expected, but instead contain a chaotic jumble of repetitive segments and fragments that are genetic fragments that accumulate in the plant.

eighty-five percent C.richardii The genome is made up of these transposons, which are DNA sequences that can move around, and this ratio is also A. capillus-veneris.

“Functional genes are separated by a lot of repetitive DNA,” says Pam Soltis, a botanist at the Florida Museum of Natural History.

“Although we are not sure how Ceratoptera And that other fern genomes have become so large, apparently, that the common view of recurrent episodes of genome duplication is not supported. “

Whatever happened, this seems to suggest that ferns are inefficient at shedding junk DNA. Instead, they keep it indefinitely, like a hoarder who has no idea when that drawer full of dry pens can be used.

But the team also found evidence that C.richardii Is a sneaky little DNA thief.

In the genome of ferns, there is a defense mechanism against a specific toxin that punches holes in the cell membrane. These defenses are normally found in bacteria — suggesting that ferns acquired them from bacteria through a process called horizontal gene transfer (which is actually quite common in bacteria).

Copies of these defense genes appeared in different parts of the plant, suggesting that this transfer occurred multiple times. The researchers therefore believe that ferns do appear to gain some benefit from the fruit of their trophies, and that benefit is likely defensive as well.

And also quite surprising and ingenious.

“The mechanisms behind horizontal gene transfer remain one of the least studied areas of terrestrial plant evolution,” Soltis said.

“On an evolutionary timescale, it’s a bit like winning the lottery. Anytime a plant is injured, its interior is vulnerable to microbial invasion, but it seems amazing that their DNA is integrated into the genome.”

You’ll never look at your fern the same way again.

papers on A. spinulosa, A. capillus-venerisand C.richardii Posted in natural plants. They can be found here, here and here respectively.

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