Gene editing to boost breeding of new crops

Scientists from the University of Maryland College of Agriculture and Natural Resources have developed a method to edit multiple genes in plants while simultaneously changing the expression of other genes.

This new tool will enable genetic engineering combinations that work together to boost functionality and improve breeding of new crops.

Ten years ago a new technology called CRISPR-CAS9 made it possible for scientists to change the genetic code of living organisms.

As revolutionary as it was, the tool had its limitations, only performing one function: removing or replacing genes in a genetic sequence.

Boffins later developed another function that allowed them to change gene expression by turning them on or off, without removing them from the genome. But each of these functions could only be performed independently in plants.

Now the Maryland scientists have developed CRISPR-Combo, a method to both edit multiple genes in plants while simultaneously changing the expression of others.

“The possibilities are really limitless in terms of the traits that can be combined,” said Yiping Qi (pictured above), an associate professor in the Department of Plant Science and Landscape Architecture and co-author of the study.

“But what is really exciting is that CRISPR-Combo introduces a level of sophistication to genetic engineering in plants that we haven’t had before.”

The benefits of manipulating more than one gene at a time can far outweigh the benefits of any one manipulation on its own.

For example, imagine a blight raging through wheat fields, threatening farmer livelihoods and food security.

If scientists could remove a gene from the wheat that makes it susceptible to the blight and simultaneously turn on genes that shorten the plant’s life cycle and increase seed production, they could rapidly produce blight-resistant wheat before the disease had the chance to do too much damage.

Professor Qi said: “As a proof of concept, we showed that we could knock out gene A and upregulate, or activate, gene B successfully, without accidentally crossing over and knocking out gene B or upregulating Gene A.”

CRISPR-Combo was tested on a flowering plant called rockcress (Arabidopsis), which is often used by researchers as a model for staple crops like corn and wheat.

The researchers edited a gene that makes the plant more resistant to herbicides while activating a gene that causes early flowering, which produces seeds more quickly.

The result was an herbicide-resistant rockcress plant that yielded eight generations in one year rather than the ordinary four.

The team also demonstrated how CRISPR-Combo could improve efficiency in plant breeding using tissue cultures from poplar trees.

Breeding programmes to develop new varieties of plants generally use tissue cultures rather than seeds –consider how a plant can regrow roots and leaves from a single stalk planted in the soil.

Scientists genetically modify stem cells from plant tissue that have the ability to grow into full plants, and when those plants mature and produce seeds, the seeds will carry on the genetic modifications.

Some plants are better at regenerating from tissue cultures than others, which makes this step the single largest bottleneck in genetic engineering of crops. For some plants the success rate is just one per cent.

Professor Qi and his team addressed the bottleneck by first editing a few traits in poplar cells, then activating three genes that promote plant tissue regeneration.

“We showed in poplars that our new method could offer a solution to the tissue regeneration bottleneck, dramatically increasing the efficiency of genetic engineering,” he said.

Currently, growing genetically engineered plants from tissue cultures requires the addition of growth hormones, which activate growth promoting genes.

The research team shortcut this process in rice by directly activating these genes with CRISPR-Combo.

The result was gene-edited rice from tissue cultures that did not require hormone supplementation.