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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.
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