How bread wheat got its gluten: tracing the effect of a long-lost relative on modern bread wheat

Genetic detective work has revealed an obscure ancestor of modern bread wheat, in a find similar to revealing a famous long-lost relative through DNA analysis in humans.

In a study published in Nature Biotechnology, researchers sequenced the DNA from 242 unique accessions of Aegilops tauschii collected over decades from its entire original range – from Turkey to Central Asia.

Population genome analysis led by Dr. Kumar Gaurav of the John Innes Center revealed the existence of a distinct lineage of Aegilops tauschii confined to present-day Georgia in the Caucuses region – about 500 kilometers from the fertile crescent where wheat was first cultivated – an area that stretches across modern Iraq, Syria, Lebanon, Palestine, Israel, Jordan and Egypt.

The first author of the study in Nature Biotechnology, Dr. Kumar Gaurav said: “The discovery of this unprecedented contribution to the bread wheat genome is akin to the discovery of the introgression of Neanderthal DNA into the human genome of Africa.”

“It is most likely that it happened through a hybridization outside the fertile crescent. This group of Georgian acclimations forms a distinct lineage that contributed to the wheat genome by leaving a footprint in the DNA.”

The discovery comes through a major international collaboration to improve crops by exploring useful genetic diversity in Aegilops tauschii, a wild relative of bread wheat. The Open Wild Wheat Consortium brought together 38 research groups and researchers from 17 countries.

Further research conducted by Dr. Jesse Poland’s group at Kansas State University was published in an accompanying paper in Communications Biology and shows that the ancestral Aegilops tauschii DNA found in modern bread wheat includes the gene that gives the dough superior strength and elasticity.

Dr. Poland said: “We were amazed to discover that this lineage has yielded the best known gene for superior dough quality.”

Researchers speculate that the newly discovered genus may have been more geographically widespread in the past and that it may have been separated as a refugee population during the last ice age.

After reflecting on all that has come together to make this work possible, Dr. Brande Wulff, the author of the study, “50 or 60 years ago, at a time when we barely understood DNA, my scientific ancestors traversed the Zagros Mountains in the Middle East and Syria and Iraq. They collected seeds and perhaps had a clue, “They could one day be used to improve wheat. Now we’re so close to unleashing that potential, and for me it’s extraordinarily exciting.”

Deciphering the complex genome of wheat

Modern “hexaploid” wheat is a complex genetic combination of different grasses with a huge genetic code, divided into A, B and D sub-genomes. Hexaploid wheat makes up 95% of all cultivated wheat. Hexaploid means that the DNA contains six sets of chromosomes – three pairs of each.

Through a combination of natural hybridizations and human cultivation, Aegilops gave the tauschii D genome to modern wheat. The D genome added the properties of dough making and allowed bread wheat to flourish in different climates and soils.

The origins of modern hexaploid bread wheat have long been the subject of intense study with archaeological and genetic evidence suggesting that the first wheat was cultivated 10,000 years ago during the fertile crescent.

Domestication, while increasing yields and increasing agronomic performance, came at the expense of a pronounced genetic bottleneck that erodes the genetic diversity of protective properties found in Aegilops tauschii, such as disease resistance and heat tolerance.

Analysis performed by Dr. Gaurav and the research team revealed that only 25% of the genetic diversity found in Aegilops tauschii turned into hexaploid wheat. To explore this diversity in the wild gene pool, they used a technique called association mapping to discover new candidate genes for disease and pest resistance, yield, and environmental resilience.

Dr. Sanu Arora, who had previously led a study to clone disease resistance genes from Aegilops tauschii, said: “Previously, we were limited to exploring a very small subset of the genome for disease resistance, but in the current study, we have generated data and techniques to make an independent exploration of species diversity ”.

Further experiments showed the transfer of candidate genes for a subset of these traits to wheat by means of genetic transformation and conventional crossing – facilitated by a library of synthetic wheat – specially bred material incorporating Aegilop’s tauschii genomes.

This publicly available library of synthetic wheat captures 70% of the diversity found across all three known Aegilops tauschii genera, allowing researchers to quickly assess properties in a background of hexaploid wheat.

“Our study provides an end-to-end pipeline for the rapid and systematic exploration of the Aegilops tauschii gene pool for the improvement of modern bread wheat.” says Dr. Wulff.

This research is part of a global collaboration to improve crops by exploring useful genetic diversity in Aegilops tauschii, a wild relative of bread wheat. The Open Wild Wheat Consortium brings together 38 research groups and researchers from 17 countries

The image at the top of the page shows researchers on a wild wheat relatives foraging trip in the central Zagros Mountains in western Iran. Credit – Ali Mehrabi

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