Nearly 80 percent of the food that feeds the world begins as seeds, including such staple crops as corn, wheat and rice. Despite the importance and ubiquity of seeds, researchers have discovered precious little about the processes that regulate plant fertilization, the essential first step in seed formation.

Now, Howard Hughes Medical Institute (HHMI) researchers have identified a key molecular signal that regulates the growth and guidance of the "pollen tube," a tunnel formed by the pollen grain that aids in fertilizing the plant's eggs. They say their initial findings could open a new route to understanding the multitude of interacting control signals that likely guide the pollen tube on its crucial journey.

In an article published in the July 11, 2003, issue of the journal Cell, HHMI investigator Daphne Preuss and her colleagues at the University of Chicago report that the molecule gamma-amino butyric acid (GABA), best known for its role as a neurotransmitter in the mammalian nervous system, is a key signaling molecule that triggers plant reproduction.

"When a pollen grain is deposited on the surface of a flower, it's like a speck of dust landing on the skin," said Preuss. "The fertilization process is unlike that in animals, in which the sperm swim through a well-defined cavity. Instead, this pollen grain somehow has to grow a tube from the stigma of the flower, digesting tissue to burrow all the way inside to where the eggs are.

"While a few molecules involved in this process have been identified over the years, we really still don't understand how this tube gets from start to finish," said Preuss. "And since the world's agriculture depends so profoundly on plant fertility, understanding this process is fundamentally important."

The study began when co-author Laura Brass analyzed a peculiar mutant form, called pop2, of the plant Arabidopsi
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
10-Jul-2003

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