More than 125 years ago Charles Darwin first reported that most plants grow
in a spurt during the night, not the day - and this week, scientists are
reporting the discovery of the genes that control this phenomenon.
These rhythmic growth spurts, and the ability of plants to move in response
to light, are actually controlled by genes involved in circadian rhythms ?
the "biological clock" genes that are influenced by light and dark, vary
their activity based on time of day, and are increasingly found in both
plants and animals to control a wide variety of functions, ranging from
growth to nervous system function and even fertility.

"This is an incremental but important step in understanding how plants
grow," said Todd Mockler, an assistant professor of botany at Oregon State
University, and co-author of the report with colleagues at the University of
California/San Diego and the Salk Institute for Biological Studies.

Ultimately, more understanding of these growth genetics could allow
scientists to create plants that grow faster, produce more food or have
other useful characteristics, the researchers said.

The findings will be reported this week in PloS Biology, a professional
journal. The research was funded by the National Science Foundation,
National Institutes of Health and the Howard Hughes Medical Institute.

"We now know that the expression of certain genes and hormones at night and
just before dawn is important for plant growth," Mockler said. "During the
day, the plant focuses on other tasks, such as the photosynthesis that
produces its energy. And plants are not only responding to time of day, but
also the length of daylight to control such things as flowering time and
stem length."

When such mechanisms are more fully analyzed, it may be possible to
influence them with genetic modification, Mockler said.

This advance was made possible largely by the use of DNA microarrays and
bioinformatics, most of which was done at OSU. This technology allows
powerful computers to be combined with more conventional biological research
to examine thousands of genes in an organism, in a very short period of
time, and determine which ones are active and what their role is.

Researchers now believe that almost all plant genes are expressed only at a
particular time of day, depending on the growth condition. And they use
growth and movement to maximize their chance of survival in a competitive
environment ? a plant leaf, for instance, will literally move if it becomes
shaded by another plant.

In 1880, in one of his lesser-known works that was not focused on animal
evolution, Darwin first described this phenomenon. He found that rather than
growing at a steady rate, plants often grow in regular nightly spurts.

The findings in this study were made with the plant Arabidopsis, a small
plant in the mustard family that is often used as a model for genetic
research. A glowing enzyme, luciferase, was attached to the genes that were
identified as responsible for rhythmic growth. And it would glow, on and
off, as the genes began functioning to create the hormones responsible for
growth in the dark of night.

The research program also learned that most of the genes involved in this
process have a common DNA sequence, which they called the "HUD" element for
"hormone up at dawn."

Further studies are needed to identify a protein that attaches to this HUD
element and regulates its function. Identifying that regulator, the
scientists said, could open the door to ways to control plant growth and
yield.
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