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Herbicide resistance is no longer a black box for scientists

The Pat Toraneru, depicted with millions of Amaranthus tubercii seeds, is approaching the determination of the genetic structure of herbicide resistance in problematic weed species. Credit: Fred Zwicky

When agricultural weeds evolve resistance to herbicides, they do it in one of two ways. In target site resistance, small mutations in the plant’s genetic code mean that chemicals are no longer compatible with proteins designed to attack. In non-target site resistance, plants deploy large amounts of enzymes that detoxify chemicals before they cause harm.


For scientists, resistance at the target site is easy.What they know Target protein That is, they can see directly Genetic code To understand responsible mutations. But when it comes to resistance to non-target sites, it’s a guessing game. Researchers can find out which class of enzymes detoxify chemicals, but know little about what. gene Code of those enzymes. In other words, the resistance of non-target sites is a black box.

The University of Illinois study is the first to open the box in a new way, identifying the genetic region responsible for non-target sites. Herbicide Amaranthus tubercuit resistance.

“We used a gene mapping approach Reference genome Pat Tranel, a professor and vice president and co-author of the University of Illinois School of Crop Science, said: “We were able to narrow it down to two regions of the genome: about 60 genes.”

Accurate identification of genes for non-target site resistance may provide tools for early detection and herbicide management.

“Ultimately, we want to develop an assay that farmers can use to determine if the amaranthus tuberc in their field is resistant to certain chemicals. Previous applications did not work. To see why, or to see if we’re wasting money before spraying, “said Brent Murphy, a doctoral researcher and lead author of the study. .. “These genomic assays exist for target site resistance because they know the region of the genome where these mutations reside, but until now we didn’t know where to look for non-target site resistance. ..

“Now we know that the causative gene is somewhere in these two small regions of the genome, so it’s used by growers to determine if a particular chemical needs to be sprayed. We have reached an intermediate stage in the final development of a capable assay. “

Researchers have specifically sought genes that can evade HPPD-inhibiting herbicides such as Amaranthus tubercii, a chemical commonly used in seed corn and other production systems, such as tembotrion.

To find the responsible genomic region, they crossed Amaranthus tubercii plants that were resistant or susceptible to HPPD inhibitors. Next, the grandchildren of those parent plants were exposed to HPPD-inhibiting herbicides to see how they progressed. With the complete Amaranthaceae genome available, we were able to look for commonalities between plants that survived the application of HPPD inhibitors.

“You basically ask a question. Tolerant plants, Which part of the genome do they share? And it can tell which part of the genome controls the trait of interest. We used this approach, known as gene mapping, to identify two regions of the genome that appear to be associated with resistance, “says Tranel.

Murphy was able to determine which plants had each of the two areas, and which had both.This allowed him to rank the importance of Gene region..

“Often it is known that traits are regulated by two genes, but does that mean that both genes are equally important, or one gene is 90% responsible and no longer? Does that mean that one gene is 10% responsible? That’s part of what we’re looking for. Within the genetic structure of the trait: the number of genes, where they are, and these different The relative importance of genes, “says Tranel. “Here we see a great gradual effect. If you have one area, you have a kind of resistance. If you have the other area, you have a kind of resistance. If you have both, you have a kind of resistance. , Quite resistant. In essence, resistant. Like a resistant parent. “

Researchers do not yet know which of the 60 genes are essential for HPPD inhibitor resistance, but are keeping in mind follow-up studies to further refine their search. p450 enzyme.. These have been involved in multiple studies as a major player in non-target site resistance.

“Although the p450 enzyme may still be involved, our mapping studies show that the changes that cause resistance are not in the p450 gene itself, but in the gene that regulates p450,” Tranel said. I will explain.

HPPD inhibitors are commonly used in seed corn and other corn production systems, but interestingly, they have not been used in areas where researchers have collected amaranthus tubercons for research.

“There was no history of previous field use of this chemistry, so it was really interesting to see our population resisting it. How did this develop? In most cases We expect resistance to develop as a result of some, in the form of selection pressure, but nothing obvious here, “says Murphy.

Toraneru believes that resistance of non-target sites to one class of herbicides may confer cross resistance to another. The population in this study was resistant to another class of herbicide, 2,4-D, which may have caused resistance to HPPD inhibitors.

“Why is this plant resistant to multiple herbicides? Are there common genomic changes to promote that resistance? Give farmers advice on what they can do to mitigate non-targets. So it’s very important to understand this-site resistance, because it’s still a bit black box, “Tranel says. “Target site resistance can instruct you to use herbicides with different mechanisms of action, but non-target site resistance allows different herbicides, for example, with different p450s regulated in the same way. The drug can be metabolized, which is why it needs to be further elucidated to come up with a better, more informed strategy to reduce resistance at non-target sites. “

Toraneru predicts that as more weed genomes become available, genetic maps will become the mainstay for investigating resistance to non-target sites.

“Finally, we have the tools we need to reach the roots of metabolic herbicide resistance, which is the greatest threat to modern weed management,” he says.

The article “The Genetic Structure Underlying HPPD Inhibitor Resistance in the Nebraska Amaranthus tuberculatus Population” Pest management science..


Studies explain the metabolic resistance of Amaranthus tubercii to topramison


For more information:
Brent P Murphy et al, Nebraska Amaranthus tuberculatus Population Underlying HPPD Inhibitor Resistance Genetic Structure Pest management science (2021). DOI: 10.1002 / ps.6560

Quote: Herbicide resistance is no longer the black box of scientists (August 16, 2021) August 16, 2021 https://phys.org/news/2021-08-herbicide-resistance-longer-black-scientists Obtained from .html

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Herbicide resistance is no longer a black box for scientists

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