Forests in the making

Katharina Braeutigam
Friday, August 9, 2019 - 10:16am

Plant epigeneticist Katharina Braeutigam wants to grow trees fit for a future climate.

Braeutigam studies trees at the molecular level. She researches how the plants respond to external signals such as drought, and how the plants record “memories” of the stress. She also researches how the plants respond to internal signals, specifically those that determine sex.

Braeutigam studies the balsam poplar, a dominant tree species in Canada that can be found from the very east of the country to the west and from the south to the north.

“It’s a very typical tree for Canadian forests, even more so than the maple tree. It is more widespread,” says Braeutigam, an assistant professor in the Department of Biology at the University of Toronto Mississauga.

Forest ecosystems buffer carbon dioxide levels through photosynthesis. The forests store water and release water vapour back into the atmosphere, which cools the environment around them. They are slow-growing plants that drive the planet's climate.

External signals

“Unlike us, trees are not mobile. They are fixed in place for a very long time. It is important for them to acclimate within the moment, which for a plant is its lifetime, and to adapt within the evolutionary time scale,” says Braeutigam.

She gives an example of a young poplar that experiences an unusually hot and dry summer--a heatwave combined with a drought. This affects the tree’s growth immediately. It may be smaller than its “cousins” that grew in wet and cooler years.

If this stress happens repeatedly, the tree might make a record alongside its genome. This record would give the tree the capacity to respond differently to environmental changes from the cousins that had never experienced a heatwave. In a sense, this tree would have learned and might be able to pass that on to the next generation.

“Does it teach its children? This is a hotly debated topic in biology that we call transgenerational molecular memory. We know that this happens in short-lived plants,” says Brauetigam.

Braeutigam’s poplars grow for between five to ten years before they flower and they need to flower to make the seeds that produce the next generation. Instead, Braeutigam takes cuttings from her trees and propagates them under controlled conditions in the U of T Mississauga’s research greenhouse before transplanting them outdoors.

“We have seen that they can carry over epigenetic marks or “memories” into a new plant. We have published some of this work and are continuing to work to understand how long the memory lasts, which specific positions in the genome are affected, if there are individual trees that do this more or better than others from the same population,” says Braeutigam.

Internal signals

Recently, Braeutigam with collaborators from the University of British Columbia, Agriculture and Agri-Food Canada, and the University of Guelph successfully identified a strong candidate for a master regulator of sex in balsam poplars using genomic information, epigenetic information and machine-learning.

“If the master regulator, the “switch,” is turned on, a female tree is produced. Turned off, and a male is produced. Now we are working to understand exactly how this master switch works,” says Braeutigam. “Understanding this can have implications for breeding.”

Harnessing solutions

There is a wealth of information to be learned from how the same genome can be interpreted in many different contexts such as cell types, stress situations and different ages, Braeutigam says. “It is important to study and understand and to harness the solutions that all these organisms have found to solve a certain problem.”

Forests take a very long time to produce seeds. If the environment changes too fast, they may not be able to reproduce quickly enough for standard natural selection to happen. Plants may die in their own habitat without having the opportunity to reproduce and spread, she says.

Braeutigam is fighting future forest die-back through her work to find individual genotypes that may not naturally occur in an area but that will have to be there in the future.