Grafting Technology Could Facilitate Gene Editing Across Diverse Plant Species

The time-honored method of grafting plants may hold contemporary relevance. This technique allows genetic modifications in species that are typically challenging or unfeasible to alter.

“Though it’s still in its formative stages, this technology shows immense promise,” says Hugo Logo from the University of Pisa, Italy.

Enhancing the yield and nutritional content of crops is vital to address the significant damages caused by farming practices and curbing skyrocketing food prices amid a rising global population and climate change’s impact on production. Utilizing CRISPR gene editing for precise enhancements is the most efficient approach.

However, plants present unique challenges due to their rigid cell walls, necessitating a cautious approach to gene editing. Traditional methods of plant genetic engineering involve techniques like biolistics, which shoot DNA-coated particles into plant cells, alongside employing naturally occurring genetically altered microorganisms like Agrobacterium.

These techniques typically require generating entire plants from modified cells, which is often impractical for various species, including trees such as cocoa, coffee, sunflower, cassava, avocado, etc.

Even if this method functions well, there lies another significant hurdle. When gene editing induces subtle mutations analogous to those that frequently occur in nature, regulatory bodies in certain regions may classify these plants as standard varieties, allowing them to proceed without the extensive and costly examinations required for conventional genetically modified crops. In contrast, biolistic and Agrobacterium-mediated methods often incorporate extra DNA into the plant’s genome, thus necessitating full regulatory scrutiny.

Researchers are exploring ways to refine plants without introducing superfluous DNA segments into the genome. One possibility involves utilizing viruses to deliver RNA carrying parts of the CRISPR toolkit to plant cells. However, a challenge arises since the Cas9 protein, widely used in gene editing, is substantial, making it difficult for most viruses to accommodate RNA that encodes it.

In 2023, Friedrich Kragler at the Max Planck Institute for Molecular Plant Physiology, Germany, unveiled an innovative approach. He discovered that plant roots generate a specific type of RNA capable of moving throughout the plant and infiltrating cells in the shoots and leaves.

His team modified plants to produce RNA encoding two essential components of CRISPR: a Cas protein for editing and a guide RNA that directs the editing process. They then grafted shoots from unaltered plants onto the roots of the engineered plants, demonstrating that some of the shoots and seeds underwent gene editing.

Rogo and his team regard this technique as so promising that they published a paper advocating for its further development. “Grafting enables us to harness the CRISPR system in species like trees and sunflowers,” Rogo states.

A notable advantage of grafting is its ability to unite relatively distantly related plants. For example, a tomato bud can be grafted onto a potato root. Therefore, while genetically engineering sunflower rootstocks for gene editing might not be feasible, it is plausible to engineer closely related plants to form compatible rootstocks.

Once you develop a rootstock that produces the required RNA, it can facilitate gene editing across various plants. “We can utilize the roots to supply Cas9 and editing guides to numerous elite varieties,” asserts Julian Hibbard at Cambridge University.

“Creating genetically modified rootstocks is not overly laborious since they only need to be developed once and can serve multiple species indefinitely,” he notes. Ralph Bock, also affiliated with the Max Planck Institute but not part of Kragler’s team, adds that this efficient method has wide applications.

For instance, only a limited number of grape varieties, such as Chardonnay, can be regenerated from an individual cell, making modification feasible. However, once a gene-edited rootstock is established that offers disease resistance, it will benefit all grape varieties and potentially more.

Rogo also foresees the possibility of integrating the transplant and viral techniques, where the rhizome can deliver the large mRNA of Cas9 while the virus provides the guide RNA. This way, he claims, the same rootstock could carry out various gene edits.