Trees repurpose flowering gene toolkit to control winter growth stop

The length of the growing season affects how well a tree survives winter and how much it can grow. Understanding what controls this timing is therefore important, not least for predicting how forests will respond to climate change.

Ove Nilsson and his team at the Umeå Plant Science Centre wanted to find out whether the same genes that regulate flowering in annual plants also play a role in trees and how they control growth during the season. What they found surprised them. Evolution appears to reuse the same genetic toolkit but for different purposes.

“We studied the role of the so-called ‘AP2-like’ genes. In annual plants these genes act as powerful repressors of flowering and help stop growth once the plant begins to set seeds,” explains Ove Nilsson. “We showed that these genes also control seasonal growth cessation in trees.”

Same genes, different functions

The researchers also found that these genes interact with the same molecular components in both annual plants and trees, but with opposite effects. In Arabidopsis, they repress the flowering gene FT, while in hybrid aspen they activate the corresponding gene. 

“So far, very few activators of FT expression in trees have been identified, but many repressors,” continues Jihua Ding, former postdoc in Ove Nilssons lab and now a research group leader in Wuhan, China. “We were very excited to find important activators of this ‘flowering gene’ since it is central for determing the length of the growing season in trees.”

To reach these results, the researchers CRISPR-Cas9 to switch off different combinations of AP2-like genes. They eventually created sextuple mutants in which all twelve alleles – the two copies of each of six related genes - were inactivated at the same time. 

“This work was started several years ago by previous PhD students in my lab, Maria Klintenäs and Shashank Sane, and could now be completed by Jihua Ding in her own lab in Wuhan,” says Ove Nilsson. “This knowledge can help us understand better how trees adjust their growth to the light conditions at different latitudes and may in the future support the breeding of forests better adapted to a changing climate.”