San Diego, California
March 12, 2009
Biologists at the
University of California, San
Diego have identified a key protein that links the morning
and evening components of the daily biological clock of plants.
Their discovery, detailed in the March 13 issue of Science,
solves a longstanding puzzle about the underlying biochemical
mechanisms that control plant clocks and could provide a new way
to increase the growth and yield of agricultural crops.
The finding is the first outcome of a larger effort to assemble
a complete library of all proteins called transcription factors,
which regulate genes, in Arabidopsis, a plant often used as a
genetic model.
Scientists previously had identified two primary feedback loops
in the plant daily clock - one that detects the onset of light
in the morning and another that tracks when light fades in the
evening.
"The best way to construct a robust clock would be to connect
the loops so that they both communicate that information to each
other," said Steve Kay, dean of the Division of Biological
Sciences at UC San Diego whose research team made the discovery.
"Now a protein we call CHE has provided that link."
CHE, first predicted nearly a decade ago, has proved difficult
to find.
Multiple backup systems for many important functions in plants,
including timekeeping, frustrate efforts to identify the
function of an individual molecule or gene.
"In plants there are a lot of redundancies - proteins that do
similar things," said Jose Pruneda-Paz, a postdoctoral fellow at
UC San Diego and the first author of the study. "In the clock,
on top of the redundancies, you have feedback loops that are
interconnected. So it's difficult to perturb the system."
Disrupting a protein will fail to reveal its function if the
system can compensate for its loss, so the team took a different
approach. They sorted through proteins with the ability to bind
to DNA, and therefore to regulate genes, and selected candidates
mostly likely to be part of a clock: the ones that cycle between
abundant and scarce.
Of those cyclical proteins, only CHE stuck specifically to the
part of plant DNA that controls a critical component of the
morning loop.
Further experiments demonstrated that CHE also binds to an
evening loop protein providing the missing link.
Pruneda-Paz and his co-authors "solve a major puzzle in our
understanding of the plant clock," wrote C. Robertson McClung,
professor of biology at Dartmouth College, in a commentary on
the article that will appear in the same issue of Science.
Evidence increasingly points to the clock as a critical
component of functions growth and the timing of flowering. A
recent paper published in Nature by a group at the University of
Texas, Austin reports that an altered clock contributes to
hybrid vigor, suggesting that targeting clock genes may be a way
to improve the growth of crops. "It's going to be a way to come
up with rational design for increasing yield in the field," Kay
said.
Kay expects the growing catalog of transcription factors to be
completed by the end of the year with more than 2,000 entries,
he said. "This is going to be a significant resource for the
plant science community developed here at UC San Diego."
Grants from the National Insitutes of Health supported his
team's research. |
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