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Mycotoxins - May 2008

Desjardins Dr. Anne Desjardins
From the Special Topic of Mycotoxins

According to our Special Topics analysis on mycotoxin research over the past decade, the scientist whose work ranks at #5 by total citations is Dr. Anne Desjardins, with 27 papers cited a total of 545 times. She is also ranked at #18 by total papers and #2 by cites per paper.

In Essential Science IndicatorsSM from Clarivate Analytics, her record includes 50 papers, the majority of which are classified in the field of Plant & Animal Science, cited 955 times between January 1, 1997 and December 31, 2007. She is also the author of Fusarium Mycotoxins: Chemistry, Genetics, and Biology (American Phytopathological Society Press, 2006).

Dr. Desjardins is currently a Research Chemist in the Mycotoxin Research Unit of the United States Department of Agriculture's Agricultural Research Service in Peoria, Illinois. She is also on the Editorial Board of The Journal of Applied and Environmental Microbiology, as well as a Fellow of the American Phytopathological Society and of AAAS.

In the interview below, she talks with correspondent Gary Taubes about her highly cited research.

  How did you first begin studying mycotoxins and what was the USDA’s interest at the time?

Let me first tell you about the USDA interest. Back in the late 1970s/early ‘80s, Alexander Haig was at the U.N. talking about the Russians and how they were using bio-warfare agents in Southeast Asia—yellow rain. That’s how it all started, because trichothecenes were implicated in yellow rain. That’s why the USDA started a program on these toxins.

I started working on them in 1984, specifically on these trichothecenes implicated in bio-warfare. How were they bio-synthesized? How could they be controlled? Within four or five years it became very clear that the natural occurrence of these toxins was a much more serious, real problem than any intentional distribution of them. That’s when the project took off and why it stayed funded for 25 years.

  How are mycotoxins a problem agriculturally?

History again: in 1993, there were floods in the Midwest, which really started the consistent year-to-year problems with trichothecene contamination in grain, mainly wheat. The other related issue was what we call conservation tillage, or low-tillage agriculture, which was introduced in the ‘70s and ‘80s. Most US farmers don’t plow under crop residues anymore. The reason is to conserve the soil; prevent soil erosion. The debris is left on the fields through the whole winter, and that helps keep the rain and wind from blowing off the topsoil. The downside is that certain fungi, the trichothecene-producing fungi among them, survive the winter in this crop residue.

"We went from being, in 1984, perhaps the only lab in the US doing genetics and biochemistry on these fungi, to probably one of 50 or 60 and now hundreds worldwide."

So there is the whole constellation of factors, including public awareness of mycotoxins, that kept us interested and the USDA interested. Climate change comes in here too, speculatively, and the very dominant growth of corn in this country. All of these factors led to the particular fungi that make trichothecenes, mainly Fusarium graminearum, becoming very, very well established. It’s always been around; it’s always caused problems, but now it’s exceedingly well established. The toxins are now regulated: if certain levels of trichothecenes appear in grain, it cannot be used for human food. Above certain levels it cannot be used for animal feed.

This all feeds into the continuing interest in controlling these mycotoxins. In 1988, we began working on new Fusarium species and a new Fusarium toxin, known as fumonisins, and they actually are carcinogenic, although much less so than aflatoxins. They also cause a variety of animal health problems. They’ve been tied to neural tube defects in populations that eat high levels of maize. Since 1984, we’ve worked as a multidisciplinary group, with chemists, geneticists, and biologists, studying these two kinds of toxins.

  What prompted your highly cited 1999 paper on the polyketide synthase gene required for biosynthesis of fumonisins (Proctor RH, et al., "A polyketide synthase gene required for biosynthesis of fumonisin mycotoxins in Gibberella fujikoroi slating population A," Fungal Genet. Biol. 27[1]: 100-12, June 1999)?

Our job is to characterize these toxins. Where do they occur? What fungal species make them? The second thing we do is identify the genes required for the synthesis of toxins, the biosynthetic pathways. These are complex pathways with many enzymes, many steps, and many genes. Our program has done the complete pathway for both these toxins. It’s been a very long-term effort, with lots of people involved.

Once the pathways are known and the genes are available, then we do gene function analysis. That 1999 paper was looking at the fumonisin gene, the first gene required for the biosynthesis of fumonisin. That was the first time anyone discovered a gene required for these toxins. It’s pretty straightforward and that’s why it’s so highly cited. Robert Proctor, Ronald Plattner, and I were the three main people on the fumonisin project.

  What do you find to be the most challenging aspect of your mycotoxin research?

To be perfectly honest, it’s making this long-term collaboration between biologists, geneticists, and chemists work, year after year after year. That was the hardest part of the project. It wasn’t the scientific problems. We had all the tools and the technologies and equipment we needed. The people here are very well trained. The hardest thing is to coordinate it all.

Take a project like this. You’re doing very difficult chemistry in complex agricultural matrices. You need very, very good chemists. You’re also doing cutting-edge molecular biology, so you need very, very good molecular biologists, and they’re constantly trolling for new techniques, new methods. And then everybody is working together, year after year, toxin after toxin. Then we add to this research the gene-function analysis, using gene knockouts. People do this in mice and you can do it in fungi. We were the first lab in the US to take these genetically modified, knockout fungi into the field and we saw how the actual agricultural interrelationship changes when we eliminate this gene.

This was really groundbreaking work in determining why these fungi make these very complex metabolites. But it involved, again, a whole pyramid of chemists, geneticists, and biologists, all working together over a very long period of time. I think maintaining that network was the hardest thing to do. Everyone had to feel that they were treated fairly; that they got proper credit.

  You seem obviously pleased with how it worked out.

I think we did that very successfully, yes. I think our group is very unique in that we maintained this coordinated approach on all fronts. If you can picture the whole thing: you’ve got chemists working with mass spectrometers; you’ve got cloners typing data into GenBank, then making knockout mutants, characterizing them in the lab and taking them into the field.

The field work with these mutants was done under stringent regulations from the USDA animal plant health inspection service out of Washington. They regulate any movement of genetically modified fungi. All this research had to be cleared with them. That was the whole process we did for 20 years and we did it pretty well.

  What turns out to be the function of these complex metabolites that are mycotoxins?

For trichothecenes, it turns out that they are virulence factors. If you knock out the toxin you get less disease in the plants. So the toxins are actually acting to inhibit protein synthesis in the plant, which makes it more susceptible to the disease. This was very clear in the trichothecenes situation.

"...if certain levels of trichothecenes appear in grain, it cannot be used for human food."

In fumonisins, it actually didn’t turn out to be the case. With this other class of toxin, all our field work indicated that those toxins were what you would call dispensable. It still remains a mystery what is selecting for maintaining toxin production in that population. There’s a reason these fungi make the fumonisins, but we don’t know what it is at this point. Knockout mutants are completely pathogenic. They make no toxins but cause the same level of disease in the host plants.

  How has the field and mycotoxin research evolved in the years since you published the 1999 FGB paper?

The field is just enormous now. The USDA has a Fusarium head blight initiative for wheat and barley. It’s funded by a special grant from Congress, several million dollars a year to support research on this problem. It’s huge now, or at least huge for agricultural research—we’re not the NIH.

When the USDA-NSF fungal gene-sequencing initiative started around 2001, I think Fusarium graminearum was the third fungal genome that was sequenced. That was finished in 2003. The Fusarium that makes fumonisin toxins was sequenced about two years later. These were very high priority in these genome-sequencing projects. Once the genomes were sequenced, a lot of people got interested. We went from being, in 1984, perhaps the only lab in the US doing genetics and biochemistry on these fungi, to probably one of 50 or 60 and now hundreds worldwide. It really has become huge.

  How hard is it to keep up with 50 or 60 local competitors when you used to have the field to yourself?

I try to work on unique aspects of the problem. In the last few years, I’ve tried to work more in maize and Arabidopsis. It does become more difficult when the field becomes so heavily populated. You really need to be smart and you need to pick projects that are unique and that other people aren’t working on.

  What message would you like to give to the general public about your research?

I’d have to say that it’s always important for us to stay connected with the real world and particularly with the real world of agriculture. As laboratory researchers, we have to remember who we ultimately work for. And that’s sort of a mantra for the whole USDA. We work for the public. We work for the agricultural industry. We wear two hats and we have to keep that in mind. And we need to do this better than we have. We can’t stay isolated in the research areas, where we’re not interacting with the real needs of both the public and the agricultural community.

Anne E. Desjardins
Mycotoxin Research
Peoria, IL, USA

Dr. Anne Desjardins's most-cited paper with 91 cites to date:
Proctor RH, et al., "A polyketide synthase gene required for biosynthesis of fumonisin mycotoxins in Gibberella fujikori slating population A," Fungal Genet. Biol. 27(1): 100-12, June 1999. Source: Essential Science Indicators from Clarivate Analytics.

Keywords: mycotoxins, Fusarium, fumonisins, polyketide synathase gene, trichothecenes, agriculture.


Special Topics : Mycotoxins : Dr. Anne Desjardins - Special Topic of Mycotoxins