New Tool Speeds Regeneration of Gene-Edited Citrus

Editing a plant’s genes is only half the battle. Before a new, improved trait can ever reach a farmer’s field, scientists must be able to grow a whole plant from just a few edited cells. That process can be slow, unreliable and, for some plant species, impossible. A new study describes a way to speed up that bottleneck across crops, including perennials such as citrus, strawberry, poplar and potatoes.

A multi-institutional American team developed a system called CRISPR-Combo, which allows scientists to edit a gene of interest and simultaneously activate the plant’s own natural morphogenic genes. These control how cells divide and develop into roots, shoots and eventually entire plants. Instead of inserting extra copies of these growth-promoting genes, CRISPR-Combo turns up the plant’s own version of these genes where they already sit in the genome, using the same CRISPR tool that makes the gene edit.

“Regeneration is one of the biggest roadblocks standing between a promising gene edit in the lab and a crop variety that’s actually useful to growers,” said Kranthi Mandadi, director of the Texas A&M AgriLife Research and Extension Center at Weslaco and professor in the Texas A&M Department of Plant Pathology & Microbiology. “This work shows that we can coax a plant’s own genes to regenerate faster and more reliably, and that approach holds real promise for perennial crops like citrus that have historically been very difficult to work with in the lab.”

To determine which genes were worth activating, the team first screened candidates using a fast, high-throughput hairy root system developed by AgriLife Research. The system induces root growth on plant cuttings without the lengthy process of regenerating a full plant.

In citrus, a crop notoriously resistant to transformation and regeneration, the team screened 10 candidate genes and found five that meaningfully boosted hairy root formation. In lab conditions, all five pushed shoot regeneration efficiency to 80% or higher, compared with under 60% in controls.

The findings were published in Nature Communications. The authors are Manikandan Ramasamy and Mandadi with Texas A&M AgriLife Research; Gen Li, Lei Guo, Hong Fang, Ayman Eid, Rushil Mandlik, Yanhao Cheng, James N. Culver, Gary D. Coleman, Zhongchi Liu and Yiping Qi with the University of Maryland; and Randall P. Niedz with the U.S. Department of Agriculture Agricultural Research Service in Florida.

Source: Texas A&M AgriLife