Microarray Experiments Reveal How Plants Adapt to Climate Changes
When school children learn multiplication tables and grammar - before they move on to calculus and physics - they also learn about photosynthesis. In Andrew Leakey's case, the concept of photosynthesis grabbed him by the throat and didn't let go.
"It's fascinating how plants take light and make food, in the form of sugar, and that photosynthesis is the primary producer of all energy in the biosphere," says Leakey, assistant professor of plant biology. "It's interesting both in the small scale details of photosynthesis but also how it scales up to food production and global ecology."
Broadly speaking, Leakey, a member of the Genomic Ecology of Global Change theme at IGB, is interested in understanding how processes like photosynthesis and respiration respond to climatic changes such as elevated CO2 and drought. In addition, he'd like to elucidate the gene expression that underlies the modifications in plant metabolism in response to environmental changes.
By coming to the University of Illinois in 2002, first as a Fulbright Scholar and later as IGB's first Fellow, Leakey was able to begin using genomics in his research. For example, with the help of his IGB colleagues, Leakey began to conduct microarray experiments on field-grown plants. In plant genetics microarrays were typically used in more controlled settings, such as greenhouses, and used more acute climatic conditions, such as severe drought or temperatures over a shorter time span. Little effort had been made to see if such experiments could be done outside over several growing seasons.
Leakey found that microarray experiments did indeed work in the field. For example, while it had been established that elevated CO2 resulted in greater photosynthesis and plant growth, how the sugars from carbon were used and whether efficiency of the process could be improved was unknown.
"We found that an increase in respiratory metabolism to use the products of photosynthesis was linked to an increase in gene expression for all enzymes of respiration, the mitochondrial machinery," he says. "You need gene expression to build the machine for metabolism. We didn't have that information before."
Understanding the regulation of that machine "would be a big leap forward to making plants that perform better," he says, adding that he thinks the answers could come within five years.
Leakey is also using microarray techniques to understand crop responses to drought. It is a challenge to create drought conditions in the field, but his team was able to intercept about 79 percent of the rainfall on test plots by using canvas covers on motors that blocked the rain at night, when the majority of it falls.
"The surprise was that the yield was not reduced as much as we had expected," he says of the drought experiments.
Leakey's group found that roots grew deeper than expected, but that growth at elevated CO2 somehow impaired this response. This preliminary finding challenged the previously widely held expectation that elevated CO2 enables plants to tolerate drought conditions.
Currently some of Leakey's students are looking at the role of the plant hormone ABA in these responses to drought. As the soil dries, the roots produce ABA, which acts as an early warning. It is carried from roots to shoots where it is sensed by the pores in the leaf surface. These pores then close, conserving water.
"By extracting sap and measuring the level of ABA, it gives us a measure of when a plant is signaling," says Leakey. "To really understand how and when the signal occurs will help us understand how carbon dioxide and drought control plant forms. Now we can put our finger on what is changing, which helps us really see what is causing the stomatal changes."
Leakey, who earned both his undergraduate and doctoral degrees in animal and plant sciences at the University of Sheffield (UK), was drawn to the U.S. and to Illinois because of SoyFACE (Free-Air Carbon Dioxide Enrichment), a technology enabling researchers to study the effect of long-term atmospheric changes on crops, like soybeans or corn. Researchers inject CO2 and other gases into the atmosphere of the field crops using fumigation pipes arranged in circles 20 meters in diameter. Computerized wind sensors control the release of CO2, keeping the plot at about 550 parts/million, the projected CO2 level for 2050. SoyFACE researchers are looking at how elevated CO2 affects the productivity and ecology of Midwestern agro-ecosystems, specifically crops, over the long term in open field conditions. SoyFACE is part of a network of FACE labs that extends worldwide, including Australia, Japan, China, Italy, and Sweden.
"If you want to do integrated science you need a big group of specialists at various different scales so you can learn the techniques and ask lots of questions," he says, describing the appeal of the U of I."
"These genomic techniques help us dissect all the factors and variables in a given project," he says. "The resulting information makes for increased complexity, but that's the intrigue of biology!"