Wheat science and the climate crisis

How long will we have to wait for the first wheat varieties genetically edited to resist drought? We asked geneticists gathered in Bologna to discuss the future of pasta.  

The climate crisis threatens the grain that feeds the world. If you think this is an exaggeration, think again. Wheat scientists expect a 6-7% decline in yield for every degree increase in temperature. This a decrease we cannot take lightly, knowing that wheat is the most widely grown cereal in the world and provides two and a half billion people with 20 percent of their carbohydrates and protein.

When we come to bread and pasta, meeting the challenge of food security in the coming decades will require not only smart agronomic practices but also all the knowledge that genomics can provide and the versatility of new breeding techniques such as gene editing. How difficult is the goal?

We asked two leading geneticists at the conference “From seed to pasta” organized by Roberto Tuberosa of Distal-University of Bologna in collaboration with renowned international partners, including Cymmit and Icarda (members of the CGIAR consortium, that was the driving force behind the Green Revolution of the last century) and the Wheat Initiative (launched in 2011 by the G20 countries).

Eduard Akhunov works to decipher the complexity of the wheat genome at Kansas State University and has authored major papers on the evolution of wheat. The premise is that most of the studies done in the world are on bread wheat (which has six copies of each chromosome) and not on pasta wheat (which has four copies but more biodiversity). Fortunately, however, the gap can be bridged thanks to genomics.

“The reference genome allows you to compare the gene content and identify the variants of the genes that are the same or different. Essentially, it allows you to easily transfer information almost base by base”, says Akhunov. For example, the powdery mildew resistant wheat developed in China recently is bread wheat, they knocked out the powdery mildew susceptibility gene. According to Akhunov, you could do the same with the other kind of wheat, and very likely the effects will be the same.

“I think that we need to continue sequencing. The more good genomes we have, the more accessions are sequenced and aligned, the better it is. But we need to do that strategically, trying to sample entry accessions from various countries and locations so that you could capture something that is valuable, but quite rare.”

The durum wheat pangenome project, coordinated by Tuberosa and presented at the meeting by Luigi Cattivelli, from Crea, is a great start. “You always start with the set that is representative of main breeding programs, in this case the durum community sequencing 18 tetraploid accessions, but it’s a small sample. In reality, we have a much more diverse and rich collection of accessions in germplasm, and it’s the same for bread wheat. I believe that we will continue expanding this using new genomic technologies. And this will allow us to characterize the entire spectrum of genetic diversity, including those genetic variants that are quite rare,” says Akhunov.

The thought goes to sustainability and the climate crisis: how long will it take to harness the power of genomics to edit resilience traits into wheat? “Hard to say, maybe we are not very far, I would guess, maybe four or five years. Gene editing technologies are developing very fast, becoming not only easier and more accurate, but also capable of doing more gene edits. Now we can edit hundreds of genes within a very short timeframe.”

That will allow us to start making gene edits on a large number of candidate genes and see the effects on the trait. “I think that’s what will be required for complex traits, like yield or drought tolerance. So we need to screen probably thousands of genes in different field conditions before we could tell these are the gene edits that would work. But we now have capacity from the gene editing side. And I think that there is just the matter of developing these lines and testing them in the field and I suspect that it will take three to five years”.

Not everyone is so optimistic, however. Peter Langridge, from the University of Adelaide, chairs the scientific board of the Wheat Initiative established to coordinate research on a global scale. He points out that adaptations to environmental stress are complex traits involving many genes, so they are not low-hanging fruits. The same goes for plants that will hopefully use nitrogen more efficiently and thus require less fertilizer.

“We need to make a distinction between the simple knockouts where you’re just inactivating a gene and where you want to change a gene sequence, because the regulatory requirements will be different. Moreover, we know very little still”, says Peter Langridge. There are some examples where we know more: in the case of disease resistance, there are very nice examples where modifying the gene itself generates new resistance to pests and diseases. The problem is that more drastic changes take you into a more complex regulatory framework. “Things will be easier for changes that turn off genes, for example, reducing gluten expression for the celiac disease, or changing acrylamide formation. So you have the safety advantage that comes with that”.

Langridge thinks the modifications for drought tolerance and heat stress tolerance will be much more difficult because we know so little about genetics. “However there are some encouraging signs for modifications to increase nutrient quality. For example, it would be a very important health benefit if we could increase the zinc levels in wheat”. The good news is that we can look at the way the whole genome is behaving.

“The wheat genome is incredibly dynamic. Many people think that the genetic makeup is fixed or constant. Quite the reverse. It’s quite dynamic, with rearrangement changes and genetic information from other species coming in”, says Langridge. There are going to be other approaches, he adds. “Basically we know more about domestication genes than we do about yield or drought tolerance. So let’s fix the domestication problems in wild relatives and see if we can bring in completely new germplasm with diversity”. Langridge has a re-domestication project and is quite excited: “We just got our first results from some trials, and it looks quite dramatic. So I think those sorts of things are likely to have an impact”.

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