With climate change said to bring hotter, drier growing seasons in many regions, growing crops that can source water and nutrients deeper underground will become a greater challenge.
Wheat is adapted to a variety of soils but how the structure of wheat’s roots is shaped has not been clearly understood.
Now, scientists at the University of California, Davis, have discovered that the right number of copies of a specific group of genes called OPRlll can stimulate longer wheat root growth, offering opportunities for farmers to grow healthier crops with greater yields, despite climate variables.
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They found that wheat plants with a loss-of-function variance in the gene actually showed longer roots. However, an increase in the genetic ‘dosage’, or an over-expression, reduced root growth.
“We wanted to check the genomic variances that are responsible for the differences between two wheat NILs (near isogenic lines) that showed differences in yield under both normal and drought conditions,” said Gilad Gabay, postdoctoral researcher, Department of Plant Sciences, and first author of the paper.
Near isogenic lines are strains whose genetic makeups are identical except for a few specific locations. The research revealed two NILs with a difference in copy number.
Gabay wrote in the report that increases in wheat yield are needed to feed a growing population, but losses generated by water stress are increasing with global warming and eroding progress in other areas of wheat improvement.
Root depth and biomass distribution in the soil are critical traits for adaptation to water stress. Finding ways to improve root structure have been prioritized for improving drought resilience in wheat. However, since the network of genes regulating these traits in wheat has remained undetermined, the researchers undertook studies to understand and modify wheat root design to improve sourcing water by both common (bread) wheat and durum (pasta) wheat. The priority is to produce plants that can adapt to lower water conditions and still have increased yield.
The discovery of the gene family known as OPRlll proved that different copies of these genes affect root length.
“The mechanism by which the OPRlll genes regulate root growth is by the hormone Jasmonic acid,” said Gabay.
Jasmonic acid is a naturally occurring growth regulator.
“The duplication of the OPRlll genes result in increased production of Jasmonic acid,” Jorge Dubcovsky, project leader in the Department of Plant Sciences said in the news release. “Different dosages of these genes can be used to obtain different roots.”
To stimulate the growth of longer roots, researchers used CRISPR gene-editing technology to eliminate some of the OPRlll genes duplicated in wheat lines with shorter roots. The research also included inserting a rye chromosome into common wheat, which resulted in decreased OPRlll genes, stimulated longer roots and a yield advantage during drought. However, according to the report, introducing the rye chromosome, resulted in a reduction in bread-baking quality.
“Fine-tuning the dosage of the OPRlll genes can allow us to engineer root systems that are adapted to drought, to normal conditions, to different scenarios,” said Gabay. “We used transgenic methods such as overexpression and knock-out (with) CRISPR-Cas9 to generate lines with different dosages to validate that they affect root growth in wheat.”
He wrote in the report that the field research was conducted on split-plot experiments where various test wheat varieties were grown over a four-year period, in two locations, and under both full-irrigation and terminal drought conditions.
The test wheat with the rye chromosome showed a significantly higher grain yield relative to the test wheat without the rye chromosome. They also showed increased water content and water indexes compared to the rolled leaves and dry leaf tips evident during some of the years in the adjacent plots.
In a subsequent field study, they excavated three two-metre-deep trenches by cutting perpendicular across the middle of the plots in three blocks. This allowed them to take horizontal soil core samples from the centre of each plot. These data confirmed the rye-wheat lines had a higher root density with roots reaching deeper into the soil.
He said that the removal of some of the OPRlll duplicate genes through the CRISPR process resulted in an increase in root length by more than 16 percent. Knowing the right combination of genes means researchers can search for wheat varieties that have those natural variations and breed for release to growers planting in low-water environments.
The research provides novel tools to modify wheat root architecture to withstand low water conditions.
“In many environments, increased root length is a favourable characteristic,” he said. “However, our final goal is to understand how different OPRlll dosage affects root architecture so breeders can design the root based on the target environment. In some conditions, more compacted root architecture is favourable.”
The research paper was published in Nature Communications.
