Introducing Dr. Olivia Landau, a new USDA-ARS weed scientist

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Episode transcription:

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Drew Lyon: Hello, welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production.

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My guest today is Dr. Olivia Landau. Olivia is a new research weed scientist with the USDA-ARS Wheat Health, Genetics, and Quality Research Unit. Olivia received her Ph.D. from the University of Illinois in August 2023 and moved to Pullman in April 2024. Her research interests include characterizing herbicide resistance mechanisms, identifying factors contributing to weed seed persistence in the soil seed bank, and identifying genes regulating these traits. This research aims to develop tools to predict the risk of herbicide resistance development and practices for weed seed bank management. Hello, Olivia.

Dr. Olivia Landau: Hi, Drew.

Drew Lyon: So, tell us about your background and what interested you in weed science. It’s not a field that everybody takes a liking to or even knows about.

Dr. Olivia Landau: So, yeah, I grew up in a town called Libertyville, Illinois, which is a northern suburb of Chicago, and it’s not too far away from Six Flags Great America and the Wisconsin border. And I really didn’t have much of an ag background other than my grandparents having a corn/soybean farm in central Illinois, which really just meant that I could distinguish between those two plants and I knew the meaning of crop rotation.

But growing up, I did always enjoy science, especially biology. And when it came time to figure out what I wanted to do for undergrad, my dad suggested looking into plant breeding and also that the University of Illinois has a really good crop science department, so we should just go visit and check it out.

And so that’s exactly what we did. And funny enough, I was supposed to meet with a wheat breeder there, but he had some other engagement. And so, I ended up actually meeting with Dr. Pat Tranel, who’s one of the weed scientists there, and it’s just funny in hindsight, because it kind of seems like a sign of what was to come.

So, I visited and thought like it was a lovely department and thought it was worth, you know, taking the opportunity to pursue it. And luckily I got into U of I, and as an undergrad, I had to take an introductory weed science class and I ended up really enjoying it. I enjoyed the challenge of weed ID and learning about herbicides and how plants can find ways to overcome those herbicides. And by taking that class and doing well in it that basically led to me getting my first internship with Agreliant Genetics, where they needed an intern to perform herbicide injury ratings on their corn inbred lines. So, I really enjoyed that experience. The people there were lovely, and I also enjoyed just getting to apply my weed science knowledge. And finally, that definitely inspired me to take more weed science classes.

So, that following fall I actually took a graduate level weed science class taught by my future advisor, Dr. Dean Riechers. And during that time, he kind of took notice of how much I was enjoying the class and how well I was doing, and basically offered me a job as an undergrad hourly after a quiz. So, I kind of jumped at that opportunity because I really both wanted a job and wanted more experience with research. So, that then led to me doing some undergrad research funded by the WSSA Undergrad Research Award and that involved characterizing a carfentrazone-ethyl-resistant waterhemp population.

That was a great experience just to give me an idea of what grad school is like and, you know, just weed science research in general, because you take a plant or a population of plants and you do a dose response, see a difference between that and the sensitives, then sequence that target site, look for mutations. If you see none, maybe do a malathion experiment or look at expression, what have you. So, I really enjoyed that.

It’s kind of like a murder mystery in a way. You kind of have to go through your usual suspects and, you know, think logically. And so, I really enjoyed that and that inspired me to stick around for both a masters and Ph.D. And during my masters, I actually kind of switched gears from looking at, you know, herbicide resistance in weeds to looking at herbicide tolerance in wheat, you know, wheat with an H and not weeds.

Drew Lyon: Okay.

Dr. Olivia Landau: That was a fun change of pace because you’re looking at a crop and basically, we know that wheat can detoxify synthetic auxins like halauxifen-methyl or Arylex for people who want to hear common names. And while we know it can detoxify that, the genes in wheat that encode these detoxifying enzymes haven’t really been identified and that’s kind of valuable information because you can use that for breeding programs or [to] try and determine which alleles offer the most resistance, what have you. And then also often those herbicides are used, at least in cereals, they’re used with herbicide safeners, which are pretty neat and very helpful in enhancing herbicide detoxification. That’s the generally accepted thought behind using them is that they’ll enhance the activity of these detoxification enzymes and that allows for, say, an increased rate of herbicide to be used or an increased application window.

And while they’ve been used for decades, there’s not a whole lot known exactly on how they work or what genes are necessary. And so, the nice thing with wheat is that there is an abundant amount of plant material you can use to kind of study the genome and what wheat–one type of line that we used is an alien substitution line. And with those basically, you know, wheat has 21 chromosome pairs and you can remove the endogenous chromosomes and kind of replace them with an alien genome or, sorry, the equivalent chromosome from an alien genome. And the thought was, if you had 21 lines, each one just missing one pair of chromosomes, you’re probably taking away some necessary gene needed for either the herbicide detoxification or safener phenotype and you should see a commensurate response typically. So, if we had a line that’s missing a gene needed for halauxifen-methyl tolerance, then we should see sensitivity. Or if you have a line that, you know, is missing a gene to achieve that safening phenotype, then it won’t respond to safener. You won’t protect against the injury basically.

So, well basically, I screened 21 different lines and we saw that whenever chromosome 5A is missing you see significantly more injury. But unfortunately, we didn’t see too many relevant findings for a safener basically. None of the plants lost responsiveness to safener. That’s a whole other story. There [are] probably reasons behind that, but I’ll try to keep it short so we can keep moving forward.

But basically, for my Ph.D., then we kind of pursued more with chromosome 5A. So, since we knew that was important, we kind of wanted to further confirm that by performing metabolomics experiments with liquid chromatography [and] mass spectrometry. And that’s basically going to allow you to measure herbicide detoxification over time. And so, in lines that lack 5A, you should see reduced rates of detoxification or not so much compared to lines that have 5A. And that’s what we found.

And with that knowledge of 5A being relevant, you kind of can use that to focus on, you know, certain candidate genes when you’re looking at genomic or transcriptomic data. And we did some RNA seq[uencing] and found that one of the significantly induced genes was cytochrome P450. And that made sense because they’re often involved with detoxification of synthetic auxins and as well as many other herbicides as well. But I digress.

And so, we kind of pursued this P450. We collaborated with Dr. Tom Clemente at the University of Nebraska so we could basically Crispr-edit wheat and in the hopes that we’d have lines with, like, a knockout mutation for this gene.

And we did successfully create these lines. They weren’t knockout mutations. They just had, like, a single-base insertion in the promoter, which wouldn’t really knock it out; it might affect expression. And then once you have lines like that, you can kind of phenotype them for not just changes in halauxifen-methyl tolerance, but other relevant herbicides since, you know, this P450 could potentially detoxify other herbicides.

We didn’t find any changes in halaufexin-methyl tolerance, but we did see a change in propoxycarbazone tolerance.

Drew Lyon: Oh, interesting. Not even the same mechanism of action.

Dr. Olivia Landau: Yeah, exactly. In some ways that’s surprising because again, these P450 can detoxify many different classes of herbicides. So, that was kind of the whole gist of that. And it’s very exciting. And, yeah, if you want to know more, feel free–but I assume there’s other questions you want to ask, too.

Drew Lyon: I’m sure you can go very in-depth into what you did in your masters and Ph.D. You did mention herbicide detoxification and your new position here with the USDA-ARS in Pullman. Is herbicide detoxification going to be something you continue to study here?

Dr. Olivia Landau: In short, yes, because it’s one of the most common ways weeds can achieve herbicide resistance. Basically, once you’ve confirmed [that] it’s probably not a target site-based mechanism, that’s a common thing people will explore as a non-target site-based resistance mechanism. And in the immediate future, for sure, I know Dr. Ian Burke–one of his former students characterized some Pyroxsulum-resistant Italian ryegrass populations. And I think there was a total of 30 and only 2 of them had target site mutations. And they did follow up with a bit of a malathion experiment, and it’s like, I think at least like 15 of them show some evidence of having some enhanced detoxification.

So, where I would come in definitely was kind of to perform some LCMS and see if there is some change in the rate of pyroxsulam detoxification versus like sensitive plants, which should have very little to no. So that would be–that’s the next logical step, and once we identify which populations have enhanced detoxification, we can take those lines [and] create mapping populations that we can use for genomic and transcriptomic analysis. And that’ll help identify potential candidate genes to, you know, further study and hopefully [it] functionally characterizes, you know, actually contributing to that resistance.

So, that could be P450s or it could be other detoxifying enzymes like GSTs or glucosyltransferases and even transcription factors that regulate those. So, there’s a lot to explore and it’s a little exciting.

Drew Lyon: I know early on in herbicide resistance, you know, the target site was what everybody [was interested in]. But it seems like of late a lot of herbicide resistance is this kind of metabolic resistance of these different enzymes so like all these amaranth populations and things that are resistant to glyphosate seems to be along those lines. Is that–it sounds like it’s a little bit more work figuring those out than the single target site type.

Dr. Olivia Landau: Yeah. That’s, I mean, it makes sense to always check the target site and it’s relatively easy to explore–like, you just need to know how to make primers and how to sequence and maybe do some qPCR to look at expression and copy number of a gene. But yeah, those can be relatively easy to explore. And if it is a target site-based mutation, it’s easy to screen for it too.

There’s definitely more interest now because that’s–you know, metabolic resistance has been becoming more widely reported. And there’s no reason to think that something that has a target site mutation won’t also have that mechanism as well. So, yeah, they can be compounded.

And some of like–what’s more likely to form kind of depends on the mode of action of a given herbicide—or, sorry, like basically how it inhibits the enzyme in general. So, sometimes it’s a competitive inhibitor, sometimes it’s not competitive. You know, especially those noncompetitive inhibitors like target site mutations can accumulate rapidly and have no fitness penalty. That’s kind of why there’s so many ALS or ACCase instances of resistance, because those are both noncompetitive inhibitors.

Drew Lyon: Okay. And those once they’re resistant there’s no fitness penalty so you’re unlikely to ever return to a case where your population reverts back to being susceptible again. Is that correct?

Dr. Olivia Landau: Pretty much. Yeah.

Drew Lyon: So, why is it important to understand the genetics behind a given trait, especially herbicide resistance? Why do you have to really understand that and not just know that it’s resistant?

Dr. Olivia Landau: Basically, like knowledge is power, and we really need all the knowledge we can get. And once we know the gene or genes that are involved, you can basically develop assays to detect them and figure out which alleles are versions of the gene endow resistance versus not. And once you have assays for detection, you can kind of determine how prevalent these resistance-endowing alleles are in a given area and then determine how heritable they are, determine fitness penalties, and then also determine how they’re regulated.

And in the future, you know, there’s a lot of desire to incorporate gene drive and RNAi into weed science. There’s still work to be done, but if they do work out the kinks for that, these are the types of targets they could utilize for those mechanisms basically. I think like a good example of just knowing all the details around a gene is like–especially in target site resistance, for PS2 inhibitors, we know the gene that encodes the target site is PSBA. That’s actually chloroplast encoded, so that means it’s maternally inherited, and we know that plants with this mutation in the target site have reduced photosynthetic capacity. So, that is a fitness penalty.

And when you’re not using, say, atrazine every year you can kind of see a reduction in the resistance alleles over time because they are out competed by the plants that lack this mutation in the target site. So, that would be a good example how it can inform how you go about using certain herbicides in the future.

Drew Lyon: Okay. One of the areas you mentioned is an area of interest for you is the persistence of the soil weed seed bank. Can you kind of describe what weed seed persistence is and any plans you have to study it? It is one of the aspects of weeds that makes weed management challenging is that you have this bank of seeds and until you deplete it, you continue to fight that weed.

Dr. Olivia Landau: Yep. Yep. Indeed. So, persistence is basically the seed’s ability to survive from the time it’s formed until it’s lost from the seed bank, either through germination, predation, decay, or age-related death. And what determines persistence is basically the seed’s level of dormancy and longevity and how those two traits interact with its environment. And the environment could include the weather, the temperature, agricultural practices, and what’s of more immediate interest is the microbiome.

And the microbiome is basically the microbial community that surrounds the seed. Also, the roots are relevant as well. And the reason it’s of interest is because obviously those microbes can be beneficial or kind of antagonistic. And there’s not much been done on the weed microbiome–the exception being parasitic weeds. They’ve kind of found that especially with broom-rapes, there’s certain strains of like Pseudomonas that can suppress the germination of those seeds. And I think there’s other bacteria that can interfere with the interaction between that parasitic plant and its host. So, it’s very interesting in that regard.

But as far as weeds relevant to the Pacific Northwest, there’s not been a whole lot done. And the nice thing about my research group in the ARS is that we have a lot of plant pathologists around, like Tim Paulitz, who is interested in collaborating with me and Ian Burke to kind of explore the microbiome of seeds and roots for relevant weeds. And I guess in general, we just want to take a look and see what is the difference in the microbiome between the weeds and the crops and see is there anything that could benefit us? And if, we can manipulate the microbiome through different practices. So, it’s a new territory for me because obviously I haven’t really done a whole lot of plant pathology in my life other than like intro classes in undergrad. But I’m looking forward to it and seeing how we can kind of get creative with some weed control tactics there.

Drew Lyon: Yeah, I think work in soil has been a little slow because it’s hard work, right? But we’re starting to develop some new technologies and new abilities to work in there. So, I think there’s a lot of things to learn yet and I welcome your contributions to that area. And, I welcome you to the Pacific Northwest.

I’m an Illinois native myself and so I’ve enjoyed my move to the West, and the Pacific Northwest specifically, and I think you’ll have a good time. And we look forward to seeing what new insights you can bring to us on weed management.

Is there a way our listeners can reach out to you if they’re interested in touching base with you?

Dr. Olivia Landau: Yeah. So, I’m part of the Pacific Northwest Herbicide Resistance Initiative and they have a website called pnwhri.org which has contact info for me and everyone that’s part of that group. Or you can also email me at olivia.landau@USDA.gov.

Drew Lyon: All right. We’ll get both of those addresses in our show notes so listeners can find them and reach out to you if they have questions. Thank you, Olivia.

Dr. Olivia Landau: No, thank you. And thank you for welcoming me.

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Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcast app. If you have questions or topics you’d like to hear on future episodes, please email me at drew.lyon — that’s lyon@wsu.edu — (drew.lyon@wsu.edu). You can find us online at smallgrains.wsu.edu and on Facebook and Twitter [X] @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.

I’m Drew Lyon, we’ll see you next time.

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The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University’s endorsement.