When scientists want to improve a variety of vegetables, it can take a year or less to see changes—just the length of the reproductive cycle. But reproductive improvements in trees can take years — sometimes decades — before changes become apparent.
Now, a process developed by researchers at the University of Georgia may cut that time down to a fraction.
Using the gene-editing tool CRISPR, CJ Tsai of UGA Warnell College of Forestry and Natural Resources and Franklin College of Arts and Sciences has developed a method that shortens the time it takes a poplar tree to flower, from about seven to 10 years to just a few months. By reducing this time frame, it can speed up tree reproduction to improve traits, such as cold or drought tolerance.
The results were recently published in New Botany. The paper also sheds light on how trees develop reproductive organs and opens doors to new research.
Previous methods for inducing early flowering in poplar trees have been inconsistent and labor intensive. said Tsai, professor at Winfried N. Hank Haynes, a senior fellow at the Georgia Research Alliance, said this is a major barrier to research. “But by using CRISPR technology to modify a flowering-suppressing gene, we can compress the flowering time from over seven years to three to four months, and the year-long period of flower organ development down to a few days.”
Ran Zhou, a postdoctoral researcher with Tsai, previously worked on sex determination in willows and poplars. Using his ideas, the team decides to modify the woman’s sex-switching gene into a female Poplar. They saw that this is possible with the early flowering system to bypass the long reproductive cycle of the trees. Within a few months, Tsai and her team saw new male flowers, indicating a successful sexual transformation.
The method could be a game-changer in the world of tree research, where projects can take decades compared to research on food crops. By shortening the time it takes for a tree to flower, researchers can perform controlled crosses and assess traits of interest more quickly. For example, traits that help trees better tolerate drought or temperature extremes could be tested in a smaller time frame.
Poplar trees were used in the experiment, Tsai said, because of their potential as a woody bioenergy crop, and their DNA has been fully mapped by the Energy Department. It usually takes years before the sex of the poplar tree is noticed.
“The fast-track flowering system is both crucial and timely for enabling rapid-cycle breeding and rapid-cycle genomic selection in perennial woody raw material species,” said Tsai.
Tsai and her team also noticed an additional feature in the flower development process: Female poplars have developmental potential for trimonose, or the ability to have both male and female flowers on the same plant. Poplars are usually separate male and female trees. But as it bloomed exponentially, Maria Ortega, a senior research associate at the Tsai Forest Functional Genomics Laboratory, noticed an unusual development of male flowers or full male and female flowers in the female poplars the team studied.
The CRISPR project revealed another surprising development as researchers watched flowering trees grow: an additional genetic modification showed promise in reducing the cottonseed appendages that plants use to spread their seeds each spring.
The white, feathery growths can be a nuisance as they fall off — or a nightmare for allergy sufferers. By blocking specific selection and the flowering gene, Tsai’s team found that cottony attachments are almost non-existent.
While the process requires further study, it could be a positive change for allergy sufferers in the future. “This provides a molecular basis for the development of hairless seeds, which can reduce the spread of allergens in urban areas or through working forests,” she added.
Not only did the change in seed hairs help confirm the process, but it created new opportunities for exploring how trees mature and reproduce. Tsai said she is excited about the new possibilities.
“This work has opened up a lot of new opportunities for research into key reproductive traits,” she said. “And a smaller time frame can give students more opportunities for their own research projects, rather than starting something that takes years or a decade to produce results.”
Besides Tsai, the paper’s co-authors were Zhou, lab research technician Margot Chen, postdoctoral researcher Patrick Beuge, and senior researcher Bindu Simon. Ortega was the paper’s main author.