“The holy grail” of crop transformation: UK researchers develop wheat genetic modification system

04 Nov 2019 --- Researchers at UK-based John Innes Centre (JIC) have developed an open-source reproducible Agrobacterium-mediated transformation system for the spring wheat cultivar “Fielder” (Triticum aestivum L.). While transformation efficiency for wheat has languished around 5 percent for many years despite its global importance, the new system can yield efficiencies of up to 25 percent of those generally achieved using comparable systems.

“We knew from the onset that it was going to be difficult to develop and optimize a wheat transformation protocol. We took it step-by-step, planning our next experiments from the results of the previous ones. What has been surprising is the demand for wheat transformation from the research community. The BRACT transformation lab, here at JIC, offers wheat transformation as a service to researchers and keeping up with the demand is challenging,” Dr. Sadiye Hayta, Postdoctoral Scientist at JIC and the study’s lead author tells FoodIngredientsFirst.

Wheat is the most difficult crop to transform.Impact on the food industry
While wheat remains the most difficult of all major crops to modify genetically, it is no less of a staple ingredient in feeding an ever-ballooning global population. Wheat is grown on more land area than any other commercial crop, with global production at 700 million metric tons, according to data from the UN’s Food and Agriculture Organization (FAO).

Although genetically mutated foods and crops often face strict regulations and legislation, Dr. Hayta predicts their wheat transformation process may indirectly impact the food industry. Their discoveries can then be used in traditional wheat breeding systems to produce better performing varieties of wheat, for example, exhibiting more disease and drought resilience or higher yields during adverse growing conditions. The latter is becoming increasingly more critical because of the rapid onset of concerning climate change and the rising global population.

The JIC study, published in the Plant Methods journal, is the product of six years of research. It revealed an optimized, reproducible Agrobacterium-mediated transformation system for the spring wheat cultivar ‘Fielder’ that yields transformation efficiencies of up to 25 percent. Some of the most significant factors influencing transformation efficiency include donor material, pre-treatment by centrifugation, vector type and selection cassette. 

After five weeks growing in Petri dishes, the wheat embryos regenerated shoots with visibly strong roots. The highly efficient and repeatable transformation system for wheat has already been used to introduce genes of interest and for CRISPR–Cas9 based genome editing.

Difficult to transform
The wheat genome is extremely complex, at five times the size of the human genome, says Dr. Hayta. Methods reported in the literature on wheat transformation remained around 5 percent for many years. This is due to wheat’s genetic characteristics, both its large and complex genome as well as its reluctance to regenerate through tissue culture. 

If a selected wheat embryo is too small, it may regenerate into plants well, but transfer DNA less. Vice versa, slightly more mature embryos accept the DNA well but do not regenerate as well. Finding the sweet spot within the embryo selection remains a difficult challenge. Sometimes, the researchers were presented with a window of opportunity of only a few days to select the correct wheat embryos. 

Given its genetic complexity and narrow window of opportunity to transform, Dr. Hayta calls wheat “the holy grail” in terms of transformation. “With some plants like barley there is more leeway, for example – they are more forgiving in culture,” Dr. Hayta notes. However, wheat remains a particular challenge in the crop transformation space.

The embryos have to be large enough to work with, but not too large in case they do regenerate well enough.“Through our research, we have tried to address many of these limiting factors to produce an efficient and reproducible wheat transformation system for the wheat research community. In our paper, we meticulously describe the exact growing conditions of donor plants and explain in much detail the growth stage and size of the embryo to select. We also included detailed pictures and a small video to help wheat researchers,” Dr. Hayta explains. 

Wheat transformation also opens the way for new genome editing technologies based on CRISPR/Cas. These genome editing technologies rely on transformation to introduce very precise edits to the plant genome. Genome editing technologies allow the breeder to achieve desired traits while shaving years off the process of traditional breeding. The first genome-edited crop, a Brassica, was released in the US early this year, says Dr. Hayta. 

Further research
With an eye on the future of crop transformation, Dr. Hayta states that new genome editing technologies based on the CRISPR/Cas systems are very fast-moving fields in R&D. “Our lab is already using CRISPR/Cas systems to genome edit wheat amongst other crops, such as barley, brassica and tomato. We can now do things that we could only dream of doing a few years ago. This wheat transformation method should enable the advancement of genome editing technologies in wheat,” Dr. Hayta concludes. 

DNA coding and genetic modification is a wide-spanning field of research which may offer solutions to end global hunger and feed growing populations. Research from the UK showed that rider retrotransponsons, or jumping genes, alter the gene expression and physical characteristics of plants. This could allow crops to better cope with more extreme conditions driven by the changing climate, such as helping to make them drought-resistant. 

Scientists at the Agricultural Research Service (ARS) and the Boyce Thompson Institute (BTWI) identified rare taste-enhancing gene in tomatoes. The researchers say breeders should be able to increase the flavor of store-bought, mass-produced tomatoes while preserving the traits that make them an economically advantageous crop. 

By Anni Schleicher