Ghent, Belgium
October 23, 2008
VIB researchers
at Ghent University have discovered the substance that governs
the formation of root offshoots in plants, and how it works.
Root offshoots are vitally important for plants – and for
farmers. Plants draw the necessary nutrients from the soil
through their roots. Because they do this best with a
well-branched root system, plants must form offshoots of their
roots at the right moment. The VIB researchers describe how this
process is controlled in the prominent professional journal
Science. A key player in this process is a protein called ACR4.
Depending on the signals that it receives from its environment,
this protein triggers the formation of a root offshoot. Now that
we know the control mechanism, we can begin to stimulate plant
roots to form more, or fewer, offshoots. This can lead to a more
ecological agriculture and to the production of better crops at
the same time.
An efficient network
It is difficult to overstate the importance of
plants in our lives − they are responsible for our oxygen and
for food, clothing, energy, and countless other things. And in
turn, the importance of a plant’s roots is unquestionable: they
provide the plant with necessary nutrients and moisture. The
more the roots are subdivided, in breadth and depth, the better
they can do their work. So, a well-coordinated, controlled
formation of root offshoots is crucial to a plant. But, until
now, how a plant determines when and where an offshoot should be
formed was unknown.
Asymmetric cell division
The presence of stem cells is
very important in the development of plants and animals. Stem
cells are cells that can transform themselves into various types
of cells. In animals, tissues and organs are formed before
birth; but in fully-grown plants, stem cells continue
to play a major role in the formation of new organs or tissues,
such as root offshoots.
These stem cells are found
inside the root, and several of them will induce the formation
of an offshoot. These ‘root-founder’ cells undergo an
asymmetric cell division.
In contrast to the usual cell division, which gives rise to two
identical cells, asymmetric cell division produces two different
cells: a stem cell that is identical to the original cell, and a
cell that is ready to become a specialized cell – in this case,
a secondary root cell.
The
decisive signal
With the aid of the mouse-ear
cress (Arabidopsis thaliana), a frequently used model
plant, Ive De Smet and
Valya Vassileva in
Tom Beeckman’s group
have been studying how a plant determines which cells will
trigger offshoots. To do this, the VIB researchers in Ghent have
employed a special technology that makes it possible to make
synchronous offshoots develop at different moments. This allowed
them to isolate the cells that induce the formation of
offshoots. They found out which genes are active in these cells
and compared them with the genes that are crucial to normal cell
division. In this way, the researchers identified a specific set
of genes that control asymmetric cell division and send the
signal for the formation of offshoots.
ACR4:
control over asymmetric division
The researchers then examined
one of these genes more closely. The ACR4
gene contains the DNA code for a receptor,
a protein that is often located on the exterior of a cell to
pick up signals from the outside and transmit them to the
controlling mechanisms within the cell. When the researchers
disrupted the function of ACR4 in plant cells, the precisely
orchestrated asymmetric cell division was also disturbed. From
this finding, De Smet and Vassileva inferred that ACR4 plays a
key role in the creation of offshoots. Because the protein has a
receptor function, triggering the formation of offshoots depends
on its reaction to signals from the environment.
Desired
or undesired
With this research, the
scientists have discovered a fundamental mechanism − fundamental
for the plant, and very important for plant-breeders as well.
This new knowledge enables us to promote, or retard, the
formation of offshoots − both activities are useful in a large
number of applications.
Promoting an extensive
root system helps plants
absorb nutrients more readily, and thus they need less
fertilizer. Such plants can also grow more easily in dry or
infertile soils. Furthermore, plants with a well-developed root
system are more firmly anchored in the soil and can be used to
counteract erosion.
On the other hand,
slowing down secondary root formation
can be advantageous in tuberous plants, like potatoes or sugar
beets. This enables these food crops to invest all their energy
in the production of nutrients. Fewer root offshoots also makes
it easier for farmers to harvest these crops.
Plant
research with medical possibilities?
This plant research sheds
light on the control of asymmetric cell division − and this kind
of cell division is similar to the cell division of stem
cells in animals, too. So,
these results can also provide greater insight into how animal
stem cells specialize.
For example, irregular cell
division plays a role in the development of various types of
cancer, and similar
control mechanisms might underlie this process as well. This is
clearly an important area for future research.
Relevant scientific publication
This research appears in the authoritative
journal Science (De
Smet et al., Receptor-like kinase ACR4 restricts
formative cell divisions in the Arabidopsis root).
Funding
This research
has been funded by: VIB, Ghent University, IWT, FWO, EMBO, UIAP,
BELSPO, and NSF.
BACKBROUNG
Tom Beeckman leads the Root Development research group in VIB’s Department of Plant Systems Biology,
Ghent University, under the direction of Dirk Inzé.
VIB
is a non-profit research institute in the life sciences. Some
1100 scientists and technicians conduct strategic basic research
on the molecular mechanisms that control the functioning of the
human body, plants, and micro-organisms. Through a close
partnership with four Flemish universities − Ghent University,
the Katholieke Universiteit Leuven, the University of Antwerp,
and the Vrije Universiteit Brussel − and a solid investment
program, VIB unites the forces of 65 research groups in a single
institute. Their research aims at fundamentally extending the
frontiers of our knowledge. Through its technology transfer
activities, VIB strives to convert the research results into
products for the benefit of consumers and patients. VIB also
develops and distributes a broad range of scientifically
substantiated information about all aspects of biotechnology.
With more than 30,000 students,
Ghent University (UGent) is
one of the largest universities in the Dutch-speaking world. The
university’s
educational offering
comprises nearly all of the academic fields that are established
in Flanders. UGent positions itself as an open, socially engaged
and pluralistic university in an international context.
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