Scientists identify the specific chromosomal regions in the wheat genome that help detoxify synthetic auxin herbicides
Since the 1960s, wheat has been known to have a natural ability to detoxify certain herbicides.
It’s a genetic trait, and if scientists could identify the genes involved, the ability could be amplified.
The problem lies with the complex wheat genetic map. Wheat contains 16 billion genes organized in three semi-independent genomes, which can overlap or substitute for each other. Isolating the genetic connection to enhance specific traits has not been simple.
In a recent study at the University of Illinois, scientists have been able to use wheat’s genetic makeup to identify the specific chromosomal regions that help detoxify synthetic auxin herbicides.
“We are working on collaboration with Corteva AgriSciences to study genes and enzymes that improve post-emergent herbicide tolerance in wheat,” said Dean Riechers, professor in the Department of Crop Sciences and co-author of the study. “One of their newer products is the herbicide halauxifen-methyl, which is why we chose to study it.”
Riechers wrote in the report that synthetic auxin herbicides are commonly used for post-emergent dicot weed control in wheat and other cereal crops. These herbicides are called synthetic auxins because they mimic the natural phytohormone that regulates almost every aspect of plant growth and development. Like other cereal crops, wheat possesses a natural tolerance to synthetic auxin herbicides, which therefore allows for selective control of dicot weeds.
“In our study, we identified a single chromosome, 5A, as being most important for halauxifen-methyl tolerance.”
The team was able to do this though a process called alien substitution. Chromosomes from one of the three wheat genomes is replaced with chromosomes from a wheat relative. One relative is Sears goatgrass (Aegilops searsii). The chromosomes are similar enough that the plant grows and looks like wheat but the benefit is that the plant may not have the same traits as the original wheat plant so this alien substitution helps pinpoint where genes of interest might lie.
“Since wheat has three genomes, it can tolerate losing a chromosome because it is replaced by the corresponding “alien” chromosome. In our case it would be 5S from Aegilops searsii,” said Riechers. “But wheat also has chromosomes 5B and 5D to help the plant compensate and grow normally. The three different genomes in polyploid wheat mean that chromosomes 5A, 5B and 5D, and the genes on each chromosome, are called ‘homoeologs,’ or that they are similar but not identical.”
The method of alien substitution is now so common in wheat research that seeds are available for research that contain the Aegilops searsii chromosomes, or S genome, substituting for each of the seven chromosomes across all three genomes. Riechers and doctoral student Olivia Obenland used them to discover that synthetic auxin tolerance is likely found somewhere on chromosome 5A.
“Although the method is common for finding genes for pathogen resistance and other useful genes in wheat, ours is the only research group to have used this method to search for herbicide tolerance,” said Riechers. “We’ve basically shortened the list from 21 chromosomes down to one so now we know where to focus our future gene discovery efforts.”
Riechers said in the news release that Obenland grew all 21 alien substitution lines in the lab greenhouse along with a wheat cultivar, Chinese Spring, and Aegilops searsii. She sprayed them with high amounts of halauxifen-methyl and then compared the treated plants with untreated controls.
While Chinese Spring showed minimal damage due to its natural detoxifying ability, Aegilops searsii reacted with a high sensitivity, as well as the wheat plants with alien substitution lines, all at chromosome 5A.
“Although we only studied these lines for herbicide tolerance, it is very likely that other types of stress tolerances have important genes located on chromosome 5A. Genes involved in conferring herbicide tolerance in wheat must have other essential functions whether it is for stress tolerance or metabolism of toxins because synthetic herbicides have only been around since the late 1940s. So, these genes must have been in the wheat genome for another purpose from a very, very long time ago.”
The research paper was published in Scientific Reports.