Ithaca, New York
September 7, 2001
Familiarity breeds contempt.
Nonfamiliarity produces seed.
Just as humans have a natural aversion toward marrying kin, some
food crop plants have genes that allow them to avoid being
fertilized by "self-related" pollen. Now Cornell University's
biologists have solved one more piece of the puzzle of how
plants' self-incompatibility works on the molecular level.
The discovery, as reported in the today's journal Science (Sept.
7, 2001), could enable genetic engineers to short-circuit the
reproduction process and more easily hybridize improved
varieties of
plants.
Many commercial crops are genetic hybrids. Obtaining seed to
plant commercial quantities of these crops, such as tomatoes,
for example, requires the labor-intensive work of manual
crossing. Without the process of manual crossing, the plants
would not have the desired qualities of hybrids. But nature has
come up with an efficient system for making hybrid seed, which,
when understood at the molecular level, can have applications on
a commercial scale. This process, termed self-incompatibility,
"prevents inbreeding and promotes out-crossing and variability
in plants," says June Nasrallah, Cornell professor of plant
biology, and the lead author on the Science paper.
In addition to Nasrallah, co-authors of "Allele-Specific
Receptor-Ligand Interactions in Brassica Self-Incompatibility"
include Mikhail Nasrallah, Cornell professor of plant biology;
Aardra Kachroo, Cornell postdoctoral researcher in plant
biology; and Christel R. Schopfer, a former Cornell postdoctoral
researcher who now conducts research in Germany. Funding for the
research was
provided by a four-year grant from the National Institutes of
Health for the purpose of understanding cellular communication
systems. The Nasrallah group examined the reproductive processes
of Brassica plants. Like humans and animal species, plants use
eggs and sperm in order to make seed and multiply. On the
plant's pistil is the stigma, which is the site for capturing
pollen. Pollen, which carries the male sperm, is released by
stamens and is carried by wind or insects, and it is drawn to a
plant's stigma.
If genetically unrelated (nonmatching) pollen lands on the
stigma, the pollen germinates and produces a pollen tube that
then runs through the plant's pistil and into the plant's
ovaries. Fertilized eggs then develop into seed ready to be
grown in a garden or a producer's field.
However, if "self-related" pollen lands on the stigma, the
stigma's outer (epidermal) layer genetically recognizes the type
of pollen and precipitates a self-incompatible reaction that
inhibits the pollen tubes from growing. The Cornell group found
that pollen recognition is based on highly specific lock-and-key
interactions between receptors (the lock) on the stigma surface
and ligands (the key) on the pollen surface. "If the pollen is
matching kin, the receptor on the stigma is activated to prevent
pollen tube growth," says Kachroo. "If the pollen is
nonmatching, the receptor is not activated and pollen tubes can
grow."
With this revelation, scientists are one step closer to
understanding the reproductive barriers of flowering plants and
their evolution. "The potential is to finally grasp -- at the
molecular level -- which genes are needed for pollen rejection,"
says Mikhail Nasrallah. "The ability to silence, mutate and
transfer the genes that control the self-incompatibility barrier
could be a boon to breeders. Even self-fertilizing crops like
tomatoes and rice can benefit from increased genetic
variability."
Contact: Blaine P. Friedlander
Jr.
Office: 607-255-3290
E-mail: bpf2@cornell.edu
Cornell University News Service
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Cornell University
Ithaca, NY 14853
607-255-4206
cunews@cornell.edu
http://www.news.cornell.edu
Cornell University news release
N3781
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