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Plants may not seem like they live the most exciting lives, but two new papers published this week point to different types of plants that are actually very cunning and manipulative. One, the parasitic dodder, steals both nutrients and DNA from its host, and the other gives leaky gut syndrome to pests that try to eat it.

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Sources:
https://www.eurekalert.org/emb_releases/2019-07/ps-pda071919.php
https://www.eurekalert.org/emb_releases/2019-07/ps-ppu071619.php
https://www.pnas.org/content/early/2019/07/16/1908748116
https://www.nature.com/articles/s41477-019-0458-0
https://www.ncbi.nlm.nih.gov/pubmed/26051213

Image Sources:
https://commons.wikimedia.org/wiki/File:Cuscuta_parasite_plant.JPG
https://commons.wikimedia.org/wiki/File:Cuscuta_europaea_bgiu.jpg
https://commons.wikimedia.org/wiki/File:Striga_root_connections.jpg
https://commons.wikimedia.org/wiki/File:Spodoptera_frugiperda_worm.jpgs
This episode of SciShow News is supported by NordVPN.

Head over to nordVPN.com/SciShow to learn more about virtual private networks and internet security. [♪ INTRO]. Plants might seem kind of dull and boring, but they are full of intrigue.

And two new papers published this week showed just how manipulative and cunning they can be. The first, published in Nature Plants, found that parasitic dodder plants from the genus Cuscuta have stolen dozens of genes from their hosts. And they don’t just take genes — they use them too.

You see, dodders are parasitic plants that don’t have chlorophyll—the pigment which captures light energy during photosynthesis. That means they can’t use light to fuel chemical reactions in their cells. So instead, they get pretty much everything they need by getting real cozy with a host plant.

They wrap around a plant’s stems and pierce them with structures called haustoria. These create direct lines to the host’s phloem — the tube-like tissue that transports nutrients down from the leaves to the rest of the plant. And nutrients and water aren’t the only thing dodders steal from their hosts.

Scientists identified 108 chunks of DNA from other plants that field dodders have added to their genomes. These genes help the dodders grow better haustoria, metabolize amino acids, and make little pieces of RNA to send back into the host to dull its defenses. This isn’t the first time scientists have found evidence for horizontal gene transfer in a parasitic plant, of course.

But the scale is noteworthy—these plants have at least twice as many stolen genes as any other genus of parasitic plant studied to date. Dodders might be better genetic thieves because their haustoria latch on to stems, where there are lots of young, healthy cells full of DNA. Other parasitic plants tend to attach to roots, which have less DNA per unit of tissue.

Also, this genetic theft didn’t happen all at once. 16 to 20 of these genes were taken by a dodder ancestor around 34 million years ago, and have been evolving in two separate lineages of dodders ever since. Other stolen genes are much more recent, which suggests this horizontal gene transfer is ongoing. That flies in the face of conventional wisdom, which is that gene transfer is rare in plants, animals, fungi, and other living things with complex, compartmented cells.

How these plants manage to pull off these heists isn’t yet clear. They have to sneak past cell walls and penetrate the protective membranes surrounding their host cells’ nuclei to get access to their genes. And understanding how they do that could teach us a lot about the inner workings of cells and genomes.

But, however they do it, it’s clear that horizontal gene transfer is an unexpected way parasitic plants can get a leg up on their hosts over time. And speaking of surprising plant abilities, a paper published this week in the Proceedings of the National Academy of Sciences suggests some plants have an ingenious long-term defense strategy against insects. They can use chemicals and spikes to give the pests leaky gut syndrome.

I’m really glad I don’t have that. That’s where the lining of the intestine is weakened and allows bits of food or bacteria to leak into other layers of tissue. When that happens, the unwelcome gunk can trigger immune responses which sap the animal’s energy, leaving less for things like growth and reproduction.

But the bacteria are the real danger — if they get where they don’t belong, they can cause a life-threatening infection. And the researchers found that’s exactly what happens to fall armyworms. The defenses of the plants they eat leave them vulnerable to infection from their own bacteria!

To figure this all out, the team raised fall armyworm larvae in a sterile lab so they didn’t have any natural gut bacteria. Then, they gave some of them food doused with 1 of 3 bacteria species often found in the animals’ guts in the wild. Other armyworms were fed sterile food so they had no gut bacteria.

They then fed the larvae 1 of 3 kinds of maize. One had long, spiky hairs on its surface called trichomes. Another produced a gut-piercing enzyme.

And the last had short, mostly harmless trichomes, so it was considered the most palatable. When the armyworms ate the spike - or chemically - defended maizes, they suffered — but it was their own bacteria that made the biggest impact. The armyworms with gut bacteria grew 60 to 76% less than the ones without gut bacteria, and up to 10x as many died, depending on the maize they ate.

They also had greater immune response, which likely explains the lack of growth. And all of this varied by the specific kind of bacteria in their gut. That suggests a plant’s defensive success depends a lot on an insect’s individual bacterial community.

Now, researchers want to better understand these microbial communities, including how they interact with plant defenses, because that could help us win the war against agricultural pests. It might allow researchers to design crops that stack defenses on top of each other to give insects leaky guts more effectively, for instance. That way, they’d be able to thwart the bugs that eat plants in a more targeted manner while reducing the use of pesticides.

Even if, in the end, we can’t really implement this knowledge, simply discovering that plants can induce this kind of syndrome in insects reveals that their interactions with animals are more complex than we used to think. And all of this goes to show that while, at times, the plant world may not seem as dramatic as the animal world, plants are every bit as conniving and ruthless. Unfortunately people can be pretty conniving and ruthless, as well, which is why it’s so important to make sure your internet service is secure.

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