Rewriting the code of wheat

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These are exciting times for wheat geneticists. Wheat has a huge hidden potential and new technologies are releasing the bottleneck in breeding. We asked Cristobal Uauy, project leader at the John Innes Centre in Norwich (UK), how genome editing is going to impact the field.

cristobalYour work is to identify genes involved in wheat productivity and to accelerate the development of improved varieties. What do you expect from the CRISPR revolution?

Genome editing has come at the perfect time for wheat. An international effort has now sequenced the complete bread wheat genome, and Italy has led on the sequencing of the durum wheat genome. We now have all the pieces in the puzzle, but we need to make sense of them. Genome editing provides a key technology to address this question by providing an experimental method in which we can target and study specific genes. The fact that wheat has three copies of every gene makes the technology even better suited since genome editing offers the possibility of altering the function of all three copies within a single plant. This is incredibly important given that in many cases mutations in a single gene copy will not be any different to the normal plant, given that the plant compensates and can still function correctly based on the remaining two copies. Hence, in many cases, we need to alter all three gene copies to see an effect. Genome editing provides an important tool in this direction. As we learn more about how genes are regulated in polyploids such as wheat it might be possible to also tweak how specific genes are expressed in certain tissues or developmental time-points. All of these approaches will allow us to learn more about how wheat functions and to develop strategies to enhance wheat’s performance in the field.

Why is the yield of wheat growing less than other cereals? Is it because of polyploidy?

For the most part, wheat and rice are both on a common trajectory and are plateauing, whereas maize is the cereal which is still on the upward. You could argue that this has to do with the level of investment in maize compared to rice and wheat. I do not think that polyploidy is holding yields back per se. Rather polyploidy has meant that breeders have selected adaptation and yield in different ways compared to diploids. In technical terms, breeders have selected dominant variation in wheat which is able to overcome all three genomes at once (for example mis-expression of the flowering signal which once started by one genome triggers flowering). In diploids, breeders have often selected recessive variation since the loss of one gene leads to a phenotype. So the exciting thing is that we can now generate recessive variation in wheat with genome editing.

Many genes controlling yield are supposed to be negative regulators, working as molecular brakes that stop the grain from growing bigger. Will genome editing help in taking those brakes off?

It will be extremely useful to take the brakes off. These “brakes” are the equivalent of recessive variation which requires all three to come off before you get an effect. So genome editing offers the prospect of allowing us to do this in a coordinated and precise manner by targeting all three genomes at once.

Is it basic science and applied science at the same time?

I think this is just science! I am not a big fan of separating basic and applied science since the application of science is a consequence of good science and time. Many of the key breakthroughs did not emerge from “applied” science but rather by scientific curiosity that then led to an application (for example Cas9 itself, technologies used in next-gen sequencing, etc). Taking the brakes off will deliver practical outcomes of immense value to breeders and growers, but at the same time it will also allow us to do fascinating science which could ultimately have an application, despite this not being the main aim.

How long it will take to go from lab to impact?

Genome editing is technically very simple and it seems to be a very universal system. This is allowing many researchers to perform genome editing across a range of crops at a relatively reasonable cost. However breeding and real-world impact are long term endeavors. If all goes well the mutant alleles need to be transferred to locally adapted varieties through back-crossing and then the lines need to be evaluated in the field for 2-3 years as is normal practice in most breeding programmes. In the future, the expectation would be that the transformation or introduction of the genome editing components would be performed directly on the most advanced locally adapted breeding lines. This would greatly accelerate the process as the back-crossing would be eliminated and the lines would already be known to be good performers. However, the current transformation technology is still very inefficient and limited to a handful of varieties. Having said this, it is a fast developing field and the ability to use any variety with equal efficiency would be a major boost to deploying genome edited wheat into the field.

Besides increasing yield, which goals are more valuable for wheat geneticists? What kind of improved varieties do you dream of?

I have lots of dreams! Overall one would want wheat plants that are able to grow in the most sustainable manner possible. This means wheat plants adapted to farming practices that allow for more efficient use of water and nutrients and for reduced pesticide use, while producing a high yielding and nutritious wheat. These are all complicated traits and many times they are antagonistic. However, I am optimistic that we will be able to make significant advances in many of these traits. Importantly, these traits all have a genetic component, but require close collaboration with other disciplines such as agronomy to ensure that the genetic potential is realized in farmers’ fields. So the dream is to understand the genetic factors controlling these traits, how they interact within the plant, and how they are influenced by the environment to ensure that they work for farmers.

You calculate that we all eat 50 wheat plants every day. That’s impressive. Is there room also for quality improvement?

Quality is essential in this discussion. This includes both processing quality to make the perfect “al dente” pasta, but also nutritional quality to ensure that humans eat nutrient dense wheat within their diets. This is especially relevant as rising CO2 is associated with decrease in nutrient content. One issue is that natural variation for micronutrients such as iron is limited so genome editing or transgenic approaches might be best suited to address some of the nutritional challenges.

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