A researcher from the Campbell laboratory prepares poplar trees for analysis. Photo by Malcolm M. Campbell
After helping to decipher the genome of the poplar tree in 2006 and finding it had 45,000 different genes, University of Toronto Professor Malcolm Campbell turned to the next logical question: What do each of the genes do? He was especially interested in understanding which genes are active in response to drought conditions. What he found was quite surprising – time of day matters to forest trees when dealing with drought.
“Each gene is like a line of code in a computer program,” Campbell explained. “Depending on which lines of code are used, the tree can create a different program to respond to environmental stimuli like drought.”
Rather than study drought-responsiveness at a single point in time, as most previous researchers have done, Campbell and student Olivia Wilkins conducted laboratory experiments where they exposed poplars to drought conditions and then examined their genes at four different times of the day and night.
“What was really intriguing was that the suite of programs that is brought to bear to contend with drought in the middle of the day is very different from those brought to bear in the middle of the night,” Campbell said. “Just as the human body reconfigures its metabolism throughout the day in response to our activities, plants must do the same thing. The stress may be constant, but because conditions change during the day, the plant must reconfigure how it responds.”
Previous research had assumed that the genes invoked in response to drought or other stresses continued to work day and night, which may have overemphasized the importance of some genes and totally missed others.
According to Campbell, understanding the genetic response to drought is crucial to helping scientists identify, conserve, and breed trees that are better able to contend with drought.
“Drought is a particularly important issue to address because trees are exposed to multiple cycles of drought over their lifetime,” he said. “Poplars are frequently riparian species, so they are particularly susceptible to fluctuations in water. We know that changes in water availability occur over the lifetime of a tree, and that is going to be exacerbated over time as climate models indicate that increasingly severe droughts will occur in different regions of the world.”
The next step for Campbell is to study genetic drought response in other tree species and to find out how drought response is affected by other stresses.