Imagine broccoli’s short, sparse and ugly cousin, and you have Arabidopsis thaliana. It is native to
Eurasia and some parts of Africa, but most consider it a weed. Fast-growing, quick flowering and able to thrive in small spaces—those traits that make it weedy are the same that make it a model plant for scientific research.
Chris Oakley, an assistant professor in the Department of Botany & Plant Pathology, has an eye that can behold the hidden beauty of such a plant. He’s spent over a decade studying the ecological genetics Arabidopsis thaliana and how it thrives naturally across different climates, his research leading him to the mountains of Sweden and the streets of Rome.
Over time, plants adapt to their local environments through slight changes in their genes, which translate to changes in the plant’s physical traits. These plants within the same species but with different adaptations suited to different native habitats are called ecotypes.
Think of how people adapt to their environments: a born-and-raised Hoosier is used to cold winters and has a bundle of heavy coats, hats and mittens at the ready. People in Florida, on the other hand, have more short sleeves, sandals and swimsuits.
Plants can’t change clothes with the seasons, however. Without the capability to move away from the cold and snow, the Arabidopsis thaliana native to Sweden, or the Swedish ecotype, is able to sense when the winter is coming and prepare with physiological changes.
“The plants experience cool temperatures and decreasing day length in the autumn, and they'll start making sugars that decrease the freezing point of their cells,” Oakley explained. “Plants have to stabilize and protect membranes. There's some proteins that are thought to decrease the formation of ice and help plants survive through freezing, too.”
Not all plants can acclimate to the cold like the Swedish ecotype of Arabidopsis can. For example, the Arabidopsis thaliana native to Rome can’t do it half as well. This Italian ecotype is more accustomed to relatively mild winters and warm, dry springs than snowy mountain sides. No need to make preparations for a freezing cold winter.
Oakley and his lab at Purdue University work with a collaborator at Uppsala University in Sweden to conduct studies of these different ecotypes of Arabidopsis. They’ve taken the plants native to Sweden and Italy and switched them around, growing them in their native environments and climates they’re not adapted to for comparison over the course of more than ten years.
The pandemic limited travel between America, Italy and Sweden. So, Gwonjin Lee and Brian Sanderson, former researchers in Oakley’s lab, had to replicate the growing conditions of the two different countries for indoor growth chambers.
“Designing simulated growth chamber programs was like creating a new world for me,” Lee said. “There's no perfect way to replicate native environments, so I had to carefully manage many environmental conditions, including air and soil temperatures, day lengths, light intensity, water amounts and specific cold periods necessary for flower development. I was repeatedly optimizing and adjusting the settings based on 13 years of climate data from native field sites in Italy and Sweden.”
One of the positives of working in a laboratory environment was the quick access to the plants for genetic analysis. Previous ecological work has focused on general regions of genes that change within a species, the latest paper published in the Proceedings of the National Academy of Sciences (PNAS) from Oakley’s lab heralds the discovery of single mutation in the Arabidopsis genome that heavily affects its ability to acclimate to the cold.
Oakley (right) talks his lab technician Mac Johnson through how to use a shaved-ice machine to quickly and evenly coat a flat of young Arabidopsis plants with a layer of snow. This freezes the whole plant at the same time, which is important for later genetic analysis. The gene encodes a transcription factor, or a protein that activates other genes, called CBF2. It’s thought to regulate several genes involved in cold tolerance in Arabidopsis. In the Swedish ecotype, CBF2 is functional and able to kick-start things like sugar accumulation when the plant senses the arrival of winter. The Italian ecotype’s CBF2 is broken and cannot perform these same tasks.
Sounds counter-intuitive, right? Why would a plant adapt by having a broken gene, especially when two-thirds of the planet freezes at some point of the year? Lee, Sanderson, Oakley and their colleagues found that cold acclimation, while keeping the plant alive through cold winter months, also came with a consequence of redistributing resources and energy—a consequence with a cost to yield.
It helps to go back to human adaptations. How well would a Hoosier’s heavy coat suit them in a humid, hot summer on the beach? Would a Floridian own the thermals and wool scarves necessary to survive an Indiana winter?
When the Swedish ecotype was grown in Italian conditions, both in the lab and in the field, it struggled. It was using too many resources to prepare for a cold spell that would never come. The Italian ecotype also struggled in cold Swedish winters without being able to acclimate to survive the harsh winter.
CBF2 helps the Swedish ecotype (SW) survive in its native snowy winters, but it's a trade-off that causes the plant to suffer when grown in a warmer Italy. Without having a functional CBF2 gene, the Italian ecotype (IT) struggles to cope with the cold of Sweden’s mountains. Oakley’s lab was able to use CRISPR-Cas9 technology to switch the CBF2 genes in the two ecotypes. There was a significant difference between the original ecotypes and the genetically-modified ecotypes growing in their simulated native environments, indicating a strong fitness, or survival, trade-off caused by cold acclimation that’s turned on by CBF2.
Oakley says these results are important for thinking about how climate change will affect plants across temperate zones. If plants sense winter is coming and make costly preparations, will this negatively affect their fitness and ability to compete with other species if no freezing happens?
According to Oakley, one possible strategy for improving resilience in plants lies in searching for more plastic plants. “Plasticity in plants is the ability to respond to changing conditions, so they're better able to perceive changing environmental conditions and change their suite of traits in response. We need plastic plants that can adjust, and there is genetic variation for plasticity that both natural and artificial selection can act on.”
- Chris Oakley, assistant professor in Botany & Plant Pathology
