To determine which genes control these rhythmic patterns of growth, the research team turned to Arabidopsis thaliana, a tiny mustard plant used as a laboratory model by plant geneticists. Because Arabidopsis, like many other plants, grows fastest in the hours before dawn when exposed to day and night cycles of light, the scientists sought to determine which of its genes were being turned on during that period. Using DNA microarray chips, they were able to test thousands of genes at a time to determine which ones were active during that period.
"We did many hundreds of thousands of measurements," said Kay, "and then asked what genes are rhythmically being turned on and are correlated with this rhythmic growth pattern just prior to dawn? What we found was that a whole bunch of genes all scattered around the Arabidopsis genome that deal with hormone biosynthesis, hormone signaling and hormone metabolism are all tightly correlated with rhythmic plant growth. This told us that this set of genes could be the actual molecular signature that defines plant growth at the molecular level."
The scientists said these disparate genes act together to regulate rhythmic plant growth much like a gate with its hinges controlled by photoreceptors and the biological clockopening in the predawn hours to allow a wave of multiple plant growth hormones to act within the cells, then closing the gate to put the brakes on plant growth until the next 24-hour cycle.
"This temporal integration of hormone pathways allows plants to fine tune phytohormone responses for seasonal and shade-appropriate growth regulation," they write in their
|Contact: Kim McDonald|
University of California - San Diego