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 JirГ Friml of the VIBdepartment
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.
Relevant scientific publication
This research appears in the online version of the authoritative journal Nature (Dhonukse et al., Generation
of cell polarity in plants links endocytosis, auxin distribution and cell fate decisions) :
nature/nature/journal/vaop/ncurrent/full/nature07409.html
JirГ Friml leads the research group auxin, polarity and patterning in VIB's Department of Plant Systems
Biology, Ghent University, under the direction of Dirk InzГ©.
(For more info, click here )
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. More info at: vib.be.
With more than 30,000 students, Ghent University (UGent) is one of the largest universities in the Dutchspeaking 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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