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 One of those traits is herbicide tolerance. Many cereal crops,
including wheat, have a natural ability to detoxify certain
herbicides applied to weeds in their midst. Under optimal
conditions, weeds die, but the crops stand tall. If scientists
can identify the genes involved, they could potentially amplify
expression of those genes to make the detoxification process
more effective under a range of environmental conditions.
In a new University of Illinois study published in Scientific
Reports, scientists take advantage of wheat’s flexible genetic
makeup to identify chromosomal regions that help detoxify
synthetic auxin herbicides.
“In the 1950s, scientists came up with a process called ‘alien
substitution’ where you can replace chromosomes from one of the
three wheat genomes with chromosomes from a wheat relative, such
as Aegilops searsii. The chromosomes are similar enough that the
plant can still grow and still looks pretty much like wheat,”
explains Dean Riechers, professor in the Department of Crop
Sciences at Illinois and co-author on the study. “The benefit is
that the relative might not have the same traits as wheat, so
the alien substitution line will help pinpoint where genes of
interest are located.”
The method is now so commonplace in wheat research that
scientists can simply obtain seeds for wheat plants with
Aegilops searsii chromosomes, denoted as the S genome, subbing
in for each of the seven wheat chromosomes across all three of
its genomes (A, B, and D). These are known as alien substitution
lines, and Riechers and doctoral student Olivia Obenland used
them to determine that synthetic auxin tolerance in wheat likely
resides 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,” Riechers says. “We've basically shortened the list
from 21 chromosomes down to one, so now we know where to focus
our future gene discovery efforts.”
Obenland grew all 21 alien substitution lines in the greenhouse,
along with wheat cultivar ‘Chinese Spring’ and Aegilops searsii,
and sprayed them all with high rates of the synthetic auxin
herbicide halauxifen-methyl. She then compared the biomass of
the treated plants to untreated controls.
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The researchers expected and observed minimal injury
in ‘Chinese Spring,’ thanks to its ability to naturally detoxify the
chemical. But Aegilops searsii turned out to be highly sensitive to
halauxifen-methyl, as were wheat plants with alien substitutions at
chromosome 5A.
“By subbing 5A with the 5S chromosome of the alien species, we took
away wheat’s natural halauxifen-methyl tolerance and made it
sensitive,” Obenland says.
Plants with the substitution at chromosome 5B also showed some
sensitivity, but only when the herbicide was applied at the highest
rate. Although this means 5B likely possesses genes involved in
synthetic auxin detoxification as well, the results so far point to
5A as the key player. Interestingly, chromosome 5D in wheat’s third
(D) genome doesn’t seem to play a major role, according to the
research.
The next step is to scour chromosome 5A for specific genes that
could be involved in herbicide tolerance. Obenland and Riechers are
already working on it, and although they’ve identified some
interesting genes related to those they’ve found in resistant
waterhemp, they’re not ready to release those results without
further molecular tests.
“Ultimately, we hope to broaden and deepen our understanding of
wheat’s natural tolerance to halauxifen-methyl, as well as other
synthetic auxin herbicides, and this is a great first step. And it
is very satisfying to apply existing genetic tools to address a new
scientific problem,” Riechers says.
The article, “Identification of chromosomes in Triticum aestivum
possessing genes that confer tolerance to the synthetic auxin
herbicide halauxifen-methyl,” is published in Scientific Reports [DOI:
10.1038/s41598-020-65434-x]. Funding support was provided by Corteva
AgriScience.
The Department of Crop Sciences is in the College of Agricultural,
Consumer and Environmental Sciences at the University of Illinois.
[Source: Dean Riechers
News writer: Lauren Quinn] |
