Leicester, United Kingdom
October 22, 2008
An enigma – unique to flowering
plants – has been solved by researchers from the
University of Leicester (UK)
and Pohang University of
Science and Technology (POSTECH), South Korea.
The discovery is reported in the journal Nature on 23 October
2008.
Scientists already knew that flowering plants, unlike animals
require not one, but two sperm cells for successful
fertilisation.
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The
image shows two pollen grains viewed by fluorescence
microscopy. A pair of red sperm cells are visible in the
normal pollen grain (top left) whilst only one red germ
cell is present in mutant pollen (bottom right). The
sperm cells are visualised using the monomeric red
fluorescent protein mRFP1 derived from a coral species.
Credit: Lynette Brownfield and David Twell, University
of Leicester |
The mystery of this ‘double
fertilization’ process was how each single pollen grain could
produce ‘twin’ sperm cells. One to join with the egg cell to
produce the embryo, and the other to join with a second cell in
the ovary to produce the endosperm, a nutrient-rich tissue,
inside the seed.
Double fertilisation is essential for fertility and seed
production in flowering plants so increased understanding of the
process is important.
Now Professor David Twell, of the Department of Biology at the
University of Leicester and Professor Hong Gil Nam of POSTECH,
South Korea report the discovery of a gene that has a critical
role in allowing precursor reproductive cells to divide to form
twin sperm cells.
Professor Twell said: “This collaborative project has produced
results that unlock a key element in a botanical puzzle.
The key discovery is that this gene, known as FBL17, is required
to trigger the destruction of another protein that inhibits cell
division. The FBL17 gene therefore acts as a switch within the
young pollen grain to trigger precursor cells to divide into
twin sperm cells.
“Plants with a mutated version of this gene produce pollen
grains with a single sperm cell instead of the pair of sperm
that are required for successful double fertilization.
“Interestingly, the process employed by plants to control sperm
cell reproduction was found to make use of an ancient mechanism
found in yeast and in animals involving the selective
destruction of inhibitor proteins that otherwise block the path
to cell division.
“Removal of these blocks promotes the production of a twin sperm
cell cargo in each pollen grain and thus ensures successful
reproduction in flowering plants.
“This discovery is a significant step forward in uncovering the
mysteries of flowering plant reproduction. This new knowledge
will be useful in understanding the evolutionary origins of
flowering plant reproduction and may be used by plant breeders
to control crossing behaviour in crop plants.
“In the future such information may become increasingly
important as we strive to breed superior crops that maintain
yield in a changing climate. Given that flowering plants
dominate the vegetation of our planet and that we are bound to
them for our survival, it is heartening that we are one step
closer to understanding their reproductive secrets.”
Researchers at the University of Leicester are continuing their
investigation into plant reproduction. Further research underway
in Professor Twell’s laboratory is already beginning to reveal
the answers to secrets about how the pair of sperm cells
produced within each pollen grain aquires the ability to
fertilize.
Prof Twell’s work, in the Department of Biology at the
University of Leicester is financially supported by the UK
Biotechnology and Biological
Science Research Council (BBSRC). |
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