Gene editing can prevent eucalyptus from becoming invasive

By Joseph Maina

May 24, 2021

Gene editing can prevent eucalyptus — a tree highly valued in Kenya and elsewhere for its hardy timber, wood fuel and medicinal extracts — from invading native ecosystems, a team of international researchers has shown.

Dr. Steve Strauss of Oregon State University led a team of scientists in the research, which concluded that the CRISPR Cas9 gene editing technique can successfully prevent the tree from sexually reproducing.

The scientists used CRISPR to knock out LEAFY, the principal gene behind flower formation, according to findings published in Plant Biotechnology Journal.

“The flowers never developed to the point where ovules, pollen or fertile seeds were observed,” Strauss said. “And there was no detectable negative effect on tree growth or form. A field study should be the next step to take a more careful look at stability of the vegetative and floral sterility traits, but with physical gene mutation we expect high reliability over the life of the trees.”

CRISPR, pronounced “crisper,” is an acronym for “clustered regularly interspaced short palindromic repeats.” CRISPR-Cas9 enables geneticists and medical researchers to edit parts of the genome by removing, adding or altering sections of the DNA sequence. Through the technique, researchers have the ability to make highly accurate changes in the DNA sequence of a living organism, basically customizing its genetic makeup.

“This could be a great means to prevent future spread from new plantings,” Strauss said. “Our work or something similar could be very useful for this goal, with the main barriers being [biosafety] regulations that might make it hard to get authorized in some countries. There would also be the challenges to genetic modification of many eucalypt species, which is often biologically difficult.”

Strauss, PhD student Estefania Elorriaga and research assistant Cathleen Ma teamed up with scientists from the University of Colorado, Beijing Forestry University and the University of Pretoria in the research. The greenhouse study involved a hybrid of two species, Eucalyptus grandis and E. urophylla, that is widely planted in the Southern Hemisphere.

“Eucalyptus is one of the most widely planted genera of forest trees, particularly the 5.7 million hectares of eucalyptus in Brazil, the 4.5 million hectares in China and 3.9 million hectares in India,” said Elorriaga, a postdoctoral researcher at North Carolina State.

Those plantings can lead to undesirable mingling with native ecosystems, note the scientists. Eliminating their ability to sexually reproduce without affecting other characteristics would be an effective way to greatly reduce the potential for invasive spreading in areas where that is considered a serious ecological or economic problem.

In Kenya, this important tree species is reputed to have a voracious appetite for water at the expense of other plant species — claims that have not been conclusively supported by scientific evidence, notes the Kenya Forest Service (KFS).

Eucalyptus is ranked among major commercial forestry species in the country, alongside cypress, pines and Grevillea, according to the Kenya Forestry Research Institute (KEFRI).  As at 2009, statistics showed that the area under eucalyptus in the country stood at 100,000 hectares.

Among its contributions to the national economy, eucalyptus provides power transmission poles for the expanded rural electrification program and is an alternative source of affordable industrial energy for the tea, tobacco, lime, cement and other industries. It contributes to increased forest cover and carbon sequestration, which mitigates against climate change. Eucalyptus also provides additional services as windbreaks, shelterbelts and boundary demarcation.

The tree’s undeserved reputation as a water hog has been the subject of spirited campaigns to weed it out of wetlands, where it is considered unsuitable due to its perceived high water consumption. Under Kenya’s Agriculture Act, it is forbidden for any agricultural landowner or occupier to grow or maintain any eucalyptus species in wetlands and riparian areas.

Image: Young women carrying shopping baskets on their heads walk past a eucalyptus plantation in Kenya. Shutterstock/Jen Watson