March 2022 - 28

Scientists seek crops that make their own nitrogen
By Samantha Murray
University of Florida
Scientists are one step closer to
giving more plants the ability to
harness nitrogen-fixing bacteria, which
would reduce the need for fertilizer,
and in turn, lower costs for farmers
and mitigate environmental impacts.
Nitrogen is an essential building
block of life. Plants can only absorb
nitrogen in some of its chemical forms.
Some of these forms of nitrogen are
naturally found in soils, but usually not
in quantities needed to reach adequate
crop yields. Nitrogen is plentiful in the
air, but in a form plants can't use.
Some bacteria that live in the soil
are able to convert atmospheric nitrogen
into one of the forms plants can use -
this is called nitrogen fixation. A few
plant species, mainly in the legume
family, have evolved root nodules
that attract and host these bacteria.
These nodules allow the plant absorb
the nitrogen the bacteria fix, and
in exchange, the bacteria get sugars
from the plant, " said Matias Kirst, a
professor of plant genomics in the
University of Florida Institute of Food
and Agricultural Sciences (UF/IFAS)
School of Forest, Fisheries and Geomatic
Sciences and a member of the UF
Genetics Institute.
" The big questions we have are, can
we teach other plants to make nodules,
and will these nodules attract nitrogen
fixing bacteria? " Kirst said.
Before these questions can be
answered, scientists need a better
understanding of how legumes, the
original nitrogen-fixing plants, form
their own nodules. Uncovering this
complex process could allow scientists
to replicate it in other plants, said
Kirst, senior author of a new study that
unpacks that process.
" When legumes come in contact
with nitrogen-fixing microbes, we
know there is a big surge in a plant
hormone called cytokinin and that
this leads to nodule formation. In this
study, we wanted to get a real-time
picture of when that surge happens
and where the activity is happening in
plants that forms nodules, " Kirst said.
To observe that play-by-play, the
research team used a technique that
causes fluorescence in the presence
of cytokinin - the area glows in the
dark - allowing researchers to see the
hormone's every move. They found
A technique that causes fluorescence
allows researchers to see how the
hormone cytokinin is involved in forming
root nodules. Photo: University of Florida
that cytokinin activity happens in two
stages. In the first stage, cytokinin is
produced in the outer layer of the root
and moves inward. In the second stage,
that inner part of the root pushes
outward like a balloon, forming the
The study also found that this
second stage of cytokinin activity
is controlled by a gene called IPT3.
They confirmed this both through
the fluorescence technique and by
observing plants that were missing the
IPT3 gene. In the plants missing the
gene, nodule formation didn't occur,
which tells the researchers that this
gene plays a key role in the process.
All plants have cytokinin and the
IPT3 gene, Kirst said.
" Biologically speaking, every plant
has the ingredients for making a
nodule, but it's a matter of expressing
the right gene at the right time and
place. This is what we're learning from
this research. We hope to apply this
understanding to developing plants
that can generate nodules, " Kirst
After that, the next big question is
whether nitrogen-fixing bacteria will
move into those nodules, Kirst said.
The study, which is published in
the journal " Plant Physiology, " was
authored by an interdisciplinary
team of researchers from UF/IFAS,
University of Wisconsin - Madison
and the Noble Research Institute. The
study was supported by a grant from
the U.S. Department of Energy. FGN
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March 2022

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