Discover could improve drought resilient wheat

• Shorter varieties are more robust

• Seeds planted deep for moisture

• No adverse effect on emergence

Semi-dwarf wheat varieties with improved drought resilience may soon be grown in fields across the world – thanks to Norfolk scientists.

Researchers at the John Innes Centre have discovered a height-reducing gene which means seeds can be planted deeper to obtain access to moisture – without the adverse effect on seedling emergence seen with existing wheat varieties.

Varieties of wheat with the Rht13 gene could be rapidly bred into wheat varieties to enable farmers to grow reduced-height wheat in drier soil conditions, said John Innes Centre group leader Philippa Borrill.

“We have found a new mechanism that can make reduced-height wheat varieties without some of the disadvantages associated with the conventional semi-dwarfing genes,” said Dr Borrill, who co-authored the study.

“The discovery of the gene, its effects and exact location on the wheat genome, means that we can give breeders a perfect genetic marker to allow them to breed more climate-resilient wheat.”

Agronomic benefits

The findings, which appear in the Proceedings of the National Academy of Sciences (PNAS), suggest that additional agronomic benefits of the new semi-dwarfing gene may include stiffer stems, making crops better able to withstand stormier weather.

Since the 1960s, reduced height genes have increased global wheat yields because the short-stemmed wheat they produce puts more investment into the grains rather than into the stems. They also have improved standing ability.

But the so-called Green Revolution genes which were bred into wheat in the 1960s also had a significant disadvantage: when these varieties are planted deeper to reach moisture in dry conditions, they can fail to reach the surface of the soil.

The newly discovered Rht13 dwarf gene overcomes this problem of seedling emergence because the gene acts in tissues higher up in the wheat stem – so the dwarfing mechanism only takes effect once the seedling has fully emerged.

Other advantages

This gives farmers a significant advantage when planting deeper in dry conditions.

The discovery of the Rht13 dwarfing gene was made possible by recent advances in wheat genomic research, principally the publication in 2020 of the Pan Genome, an atlas of 15 wheat genomes collected from around the world.

Earlier studies had identified the Rht13 locus – the region of DNA – as located on chromosome 7B on the wheat genome but the underlying gene had not been identified.

In collaboration with the group of Wolfgang Spielmeyer at CSIRO Australia, researchers used RNA and chromosome sequencing to track down the new semi-dwarfing gene.

They found a one- point mutation change – a single letter change in a sequence of DNA – and this variation on the Rht13 locus encodes an autoactive NB-LRR gene, a defence related gene, that is switched on all the time.

Experiments testing the effects of the gene confirmed that the Rht13 variation represents a new class of reduced height gene – more commonly associated with disease resistance as opposed to the widely used Green Revolution genes which affect overall growth.

“This is an exciting discovery because it opens a new way to use these autoactive NB-LRR genes in breeding in agriculture,” explains Dr Borrill.

“In dry environments, the alternative reduced height gene will allow farmers to sow seeds at depth – and not have to gamble on the seedlings emerging.

“We think the stiffer stems could result in less lodging – where stems fall over – and the upregulation of a pathogen related dwarfing gene may help to enhance resistance response to certain pathogens.”

The next step is to test how this gene works in different climates from the UK to Australia. Researchers also investigating how the mechanism works – which may be down to molecular restrictions on the cell wall preventing elongation.