A novel grafting method could allow gene editing in plants like cocoa, coffee, and avocados that are currently hard to modify. Researchers have demonstrated that engineering rootstocks to produce CRISPR components can edit shoots from non-modified plants. This approach promises broader application of precise genetic improvements for agriculture.
Gene editing with CRISPR offers precise ways to enhance plant productivity and nutrition, crucial for addressing farming's environmental impact, rising food prices, and climate challenges amid population growth. However, many plants pose difficulties due to rigid cell walls and challenges in regenerating whole plants from modified cells. Conventional techniques like biolistics—firing DNA-impregnated pellets—or using Agrobacterium insert extra DNA, triggering stringent regulations, unlike tiny natural-like mutations that regulators often treat as standard breeding.
In 2023, Friedrich Kragler at the Max Planck Institute of Molecular Plant Physiology in Germany developed an innovative solution. His team engineered plant roots to produce mobile RNAs encoding the Cas protein and guide RNA for CRISPR. By grafting non-modified shoots onto these roots, they achieved gene editing in the shoots and seeds. This leverages plants' natural RNA transport from roots to aerial parts.
Ugo Rogo at the University of Pisa in Italy, along with colleagues, highlighted this in a paper published in the International Journal of Molecular Sciences (DOI: 10.3390/ijms26199294). "It is still at the beginning stage, but this technique has great potential," Rogo said. Grafting's versatility allows combining distantly related plants, such as tomato shoots on potato roots, enabling editing of species like sunflowers, trees, cocoa, coffee, cassava, and avocados where direct methods fail.
"Grafting gives us the possibility to use the CRISPR system in trees or in plants such as sunflowers," Rogo noted. Julian Hibberd at the University of Cambridge added, "You can use the roots to deliver Cas9 and editing guides to all sorts of elite varieties." Ralph Bock, also at the Max Planck Institute, emphasized efficiency: "Making the transgenic rootstock is not a big effort, given that it just needs to be made once, and then can be used forever and for multiple species."
For grapes, where only varieties like Chardonnay regenerate easily, a modified Chardonnay rootstock could confer traits like disease resistance to all varieties. Rogo envisions hybrid approaches, using rootstocks for large Cas9 mRNAs and viruses for guide RNAs, expanding editable crops without unwanted DNA insertions.