By Kelsey Jackson

COLUMBIA, Mo. ? Without eyes or ears, plants must rely on the interaction of
molecules to determine appropriate mating partners and avoid inbreeding.

In a new study, University of Missouri researchers have identified pollen
proteins that may contribute to the signaling processes that determine if a
plant accepts or rejects individual pollen grains for reproduction.

Like humans, the mating game isn?t always easy for plants. Plants rely on
external factors such as wind and animals to bring them potential mates in
the form of pollen grains. When pollen grains arrive, an introduction occurs
through a ?conversation? between the pollen (the male part of the flower)
and the pistil (the female part of the flower). In this conversation,
molecules take the place of words and allow the pollen to identify itself to
the pistil. Listening in on this molecular conversation may provide ways to
control the spread of transgenes from genetically-modified crops to wild
relatives, offer better ways to control fertilization between cross species,
and lead to a more efficient way of growing fruit trees.

?Unlike an animal?s visual cues about mate selection, a plant?s mate
recognition takes place on a molecular level,? said Bruce McClure, associate
director of the Christopher S. Bond Life Sciences Center and researcher in
the MU Interdisciplinary Plant Group and Division of Biochemistry. ?The
pollen must, in some way, announce to the pistil its identity, and the
pistil must interpret this identity. To do this, proteins from the pollen
and proteins from the pistil interact; this determines the acceptance or
rejection of individual pollen grains.?

In the study, researchers used two specific pistil proteins, NaTTS and 120K,
as ?bait? to see what pollen proteins would bind to them. These two pistil
proteins were used because they directly influence the growth of pollen down
the pistil to the ovary where fertilization takes place.

Three proteins, S-RNase-binding protein (SBP1), the protein NaPCCP and an
enzyme, bound to the pistil proteins. This action suggests that these
proteins likely contribute to the signaling processes that affect the
success of pollen growth.

?Our experiment was like putting one side of a Velcro strip on two pistil
proteins and then screening a collection of pollen proteins to see which of
the pollen proteins have the complementary Velcro strip for binding,?
McClure said. ?If it sticks, it?s a good indication that the pollen proteins
work with the pistil proteins to determine the success of reproduction.?

In previous studies, McClure showed that S-RNase, a protein on the pistil
side, caused rejection of pollen from close relatives by acting as a
cytotoxin, or a toxic substance, in the pollen tube.

For their study, the MU team used Nicotiana alata, a relative of tobacco
commonly grown in home gardens as ?flowering tobacco.? The study, ?Pollen
Proteins Bind to the C-Terminal Domain of Nicotiana Alata Pistil
Arabinogalactan Proteins,? was published in the Journal of Biological
Chemistry and was co-authored by McClure; Kirby N. Swatek, biochemistry
graduate student; and Christopher B. Lee, post-doctoral researcher at the
Bond Life Sciences Center.

Faculty from six of MU?s colleges and schools perform interdisciplinary
research in the Christopher S. Bond Life Sciences Center with a vision to
become a recognized world-wide center of scientific excellence and
leadership in life sciences research, innovation and education. The Center
integrates the strengths of multiple, often disparate, disciplines to
promote discovery that boosts the production and quality of food, improves
human and animal health and enhances environmental quality. The Center
enriches the state of Missouri and its people by generating new businesses
and jobs, fueling the economy through the creation and dissemination of new
knowledge, and training young people to solve complex interdisciplinary
problems.
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