9 November 2019 | New Scientist | 7STICKING DNA to nanoparticles
and spraying these on plant leaves
can alter their genomes as they
grow. The simple technique
could have a wide variety of
uses, including changing the
properties of crops in fields.
“It was so straightforward,” says
Heather Whitney at the University
of Bristol in the UK. “It was really
surprising how easy it was.”
Whitney and her team have
so far tested their technique on
wheat, maize, barley and others.
They used a plant mister to spray
leaves with water containing
nanoparticles called carbon
dots that were bound to DNA.
The DNA, which coded for a
fluorescent protein, got into cells
in the plants’ leaves, prompting
them to glow green under UV
light. This is a huge advance
on conventional methods for
inserting DNA into plants.
But the DNA wasn’t
incorporated into the cells’
genomes, so should break
down over time. The researchers
then took the technique a step
further, using carbon dots bound
to DNA coding for the CRISPR
machinery used for genome
editing. In this way, they wereable to permanently edit the
genomes of sprayed leaf cells
(bioRxiv, doi.org/ddmw).
The results have yet to be
confirmed by other groups, but
if spray-on gene editing works,
it could lead to new ways of
improving and protecting crops,
and of turning plants into
biofactories capable of making
chemicals such as flavourings
and pharmaceutical products.
“It’s amazing,” says Ignacio Rubio
Somoza at the Centre for Research
in Agricultural Genomics in Spain,
who now plans to try the method.
At present, the main tool for
genetically engineering plants is
a microbe called Agrobacterium.
Researchers use it to insert DNA
into plant genomes, although it
only works in some plants and
using it outside the laboratory
would be impractical and risky.
Another approach is to use a “gene
gun” to force DNA into plant cells,
but this can damage plants and
is difficult to do on a large scale.
Whitney uses carbon dots
created by her colleague CarmenGalan. First discovered in 2004,
carbon dots are ball-like particles
of carbon less than 10 nanometres
across that can be attached to
other molecules.
Carbon dots can form when
carbon compounds burn, and
occur naturally. “We’ve found
them in coffee, we’ve found
them in soil,” says Galan.
Galan makes carbon dots for
Whitney by heating sugars in a
normal microwave oven. Next,
she attaches a polymer called
polyethylene glycol that attracts
DNA molecules electrostatically.
When sprayed on leaves, carbon
dots get into nearly every cell on
the leaf surface. Up to a third of
these cells use the added DNA to
make new proteins. Experiments
by the team show that the carbon
dots don’t seem to be toxic, and
may even boost plant growth.
So far, the team’s attempts to
modify egg cells in plant ovaries
and stem cells in growing shoots
have failed. That is a disadvantage
when it comes to creating new
varieties of GM plants. However,
it could make it safer to apply
carbon dots to fields of plants
because modifications wouldn’t
get passed to future generations
or spread among wild plants.
Many questions remain
unanswered, though, such as
how the carbon dots get into
cells. “There’s so much we don’t
know,” says Whitney.
Spray-on gene editing could
be misused, for instance to make
crops toxic. But Whitney notes
that there are already far easier
ways to poison food.
As for whether spraying carbon
dots into the environment could
harm animals, more research is
needed. Carbon dots can get into
mammalian cells growing in a
dish, says Galan, but the immune
system mops them up if they get
into the body. ❚Gene editingDEEP
OL
BYPLAINPICTURESpray-on CRISPR
Genetically modifying plants could soon be almost as easy as squirting
them with water, reports Michael Le PageIt may soon be possible
to edit the DNA of plants
simply by spraying themCosmologyLeah CraneTRAVEL far enough in the universe
and you could end up back where
you began. That is because the
universe might be a sphere rather
than a flat sheet, which would
change nearly everything we
think we know about the cosmos.
The Planck observatory, which
operated from 2009 to 2013,
mapped the cosmic microwave
background, a sea of light left over
from the big bang. It found there
was more gravitational lensing –
stretching of the light due to theshape of space-time, which can be
distorted by heavy matter – than
expected. Alessandro Melchiorri at
the Sapienza University of Rome
and his colleagues believe this could
be because the universe is “closed”,
or spherical, rather than flat (Nature
Astronomy, doi.org/ddpc).
If the universe is indeed closed,
that could be a major problem for
our understanding of the cosmos.
Another cosmological puzzle is that
the part of the universe near to us
seems to be expanding faster than it
ought to be. This is tough to explain
with a flat universe, and the team
calculated that this gets even
tougher with a spherical universe.
It is so bad that the team calls it a
“cosmological crisis”.
However, there are no other
observations hinting that the
cosmos may be closed, and
there is a chance that this Planck
measurement is a statistical fluke.
“If this [claim] is true, it would
have profound implications for
our understanding of the universe,”
says David Spergel at Princeton
University. “It’s a really important
claim, but I’m not sure it’s one that’s
backed by the data. In fact, I’d say
the evidence is actually against it.” ❚We don’t know
if the universe is
spherical or flat“ If the universe is spherical,
it could be a major problem
for our understanding of
the cosmos”