When pollen comes of age

New research from the University of Georgia has determined when pollen comes of age and begins expressing its own genome, a major life cycle transition in plants.

Each grain of pollen is actually its own multicellular organism – with two to 40 cells, depending on the species. Pollen expresses its own genome and is genetically distinct from its parent plant. That means pollen grains from a single flower can have different traits and characteristics, similar to how you might be different from your siblings.

When pollen grains compete to fertilize the egg, only those pollen grains with the most successful traits will survive to pass on their genetic information to the next generation. This fierce competition between pollen is a quality check on the genome in plants because harmful mutations are removed when the pollen grains with these mutations cannot compete.

Before the study, which landed the Jan. 28 cover of Science, scientists weren’t sure when pollen began to express its own genetic information.

“Since pollen expresses its own genome, natural selection can act directly on pollen. This makes pollen competition an important force shaping plant evolution,” said Brad Nelms, lead author of the study and an assistant professor of plant biology in the Franklin College of Arts and Sciences. “If we had better knowledge of the extent and timing of pollen selection, it would help us better predict how plant species adapt to changing environments. We might even be able to use pollen selection to speed up crop breeding, selecting for more heat-tolerant crops, for example.”

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Image: Fluorescence microscopy image of pollen (bright objects) on maize silks (long strands). New RNA sequencing results identify when this generation “comes of age” and begins its independent gene expression program. Volume 375 Issue 6579 of Science