Ghent, Belgium
October 27, 2008
VIB
researchers at Ghent University discovered how the transport of
an important plant hormone is organized in a way that the plant
knows in which direction its roots and leaves have to grow. They
discovered how the needed transport protein turns up at the
underside of plant cells. The discovery helps us to understand
how plants grow, and how they organize themselves in order to
grow. The scientific journal
Nature published the news in advance on its website.
Versatile hormone
It is known for a long time that the plant hormone auxin is
transmitted from the top to the bottom of a plant, and that the
local concentration of auxin is important for the growth
direction of stems, the growth of roots, the sprouting of
shoots. To name a few things; auxin is also relevant to, for
instance, the ripening of fruit, the clinging of climbers and a
series of other processes. Thousands of researchers try to
understand the different roles of auxin.
In many instances the distribution of auxin in the plant plays a
key role, and thus the transport from cell to cell. At the
bottom of plant cells, so-called PIN proteins are located on the
cell membrane, helping auxin to flow through to the lower cell.
However, no one thoroughly understood why the PIN proteins only
showed up at the bottom of a cell.
Endocytosis
An international group of scientists from labs in five
countries, headed by
Jirí Friml* of the VIB-department Plant Systems Biology at
Ghent University, revealed a rather unusual mechanism. PIN
proteins are made in the protein factories of the cell and are
transported all over the cell membrane. Subsequently they are
engulfed by the cell membrane, a process called endocytosis. The
invagination closes to a vesicle, disconnects and moves back
into the cell. Thus the PIN proteins are recycled and
subsequently transported to the bottom of the cell, where they
are again incorporated in the cell membrane. It is unclear why
plants use such a complex mechanism, but a plausible explanation
is this mechanism enables a quick reaction when plant cells feel
a change of direction of gravity, giving them a new ‘underside’.
Gene technology
To see the path of the protein, the researchers used gene
technology to make cells in which the PIN protein was linked to
fluorescent proteins. (This technology was rewarded with the
Nobel Prize 2008 for chemistry.) Subsequently they produced
cells in which the endocytosis was disrupted in two different
ways. The PIN proteins showed up all over the cell membrane.
When the researchers proceeded from single cells to plant
embryos, the embryos developed deformations, because the pattern
of auxin concentrations in the embryo was distorted. When these
plants with disrupted endocytosis grew further, roots developed
where the first leaflet should have been.
This research appears in the online version of the authoritative
journal Nature:
Generation of cell polarity in plants links endocytosis, auxin
distribution and cell fate decisions
Dhonukse et al.
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature07409.html
* Jirí Friml leads the research group auxin, polarity and
patterning 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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