Mitigating Plant Pandemics

It’s not easy for anyone to navigate the pandemic these days, let alone a 5.7 earthquake and then hurricane-force winds that uprooted thousands of trees in Salt Lake Valley.

Harder still when you’ve been tapped in Germany to be a new faculty member in the School of Biological Sciences… and you have a lab to launch.

Such was the case last year when Talia Karasov, an evolutionary geneticist who studies plant-microbe interactions at the Max Planck Institute in Tuebingen Germany, found herself on an airplane headed to Salt Lake City. She is part of a recent innovative hiring cluster at the University of Utah in which multiple, related academic units come together to hire researchers who study related topics in evolutionary biology. Karasov made it safely, masked and sociallydistanced, to Utah and began setting up her lab—similar to launching a startup. It’s been a whirlwind execution. Fortunately, her dog “Laika,” named after another famous traveling dog (the first to orbit earth… on the Russians’ Sputnik), has been there all along as a steadying force.

Traversing new frontiers is in the family, apparently. For Karasov, though, “going boldly where no one has gone before” is decidedly earthbound… through flora and its pathogens. Plant pathogens pose a huge problem for food security around the globe. Annually, plant pests—including microbes and insects—are responsible for 20–40% loss in agricultural yield. Decades of research on pathogen resistance has led to great success in identifying, developing and deploying pathogen-resistant crop varieties. Unfortunately, pathogens often evolve quickly to overcome these resistance traits. A common pattern has emerged in which a single genotype of pathogen evolves to circumvent resistance, and spreads widely to other populations and then globally. Once the pathogen evolves to circumvent resistance, the cycle begins anew. It’s hard if not impossible to keep up with these arms races in various cash crops, especially when the cycle of resistance/counter-resistance can happen within a few years.

This boom-bust cycle may not be inevitable, however. Indeed, anecdotal evidence from wild plant systems suggests that many (if not most) wild plants are less likely to suffer epidemics.

In her research of plant-pathogen interactions Karasov studies non-agricultural plant systems to understand which factors

are important for preventing outbreaks. Substantial evidence points to the role of diversity—genetic and environmental—in keeping plants healthy. It has been widely hypothesized that genetic diversity in plants, or the lack thereof, plays a central role in plant-pathogen epidemics. In modern agriculture, we often plant single genotypes of crops across large areas. This low genetic diversity sets up a perfect environment for a pathogen to invade and spread widely. In contrast, wild plants differ between individuals in their immune systems, and a pathogen that can infect one plant in a population may not find success in the neighboring plant that encodes a different immune complement.

Karasov’s work seeks to explicitly determine the impact of plant immune diversity on pathogen evolution and spread. “How are pathogens evolving and spreading in wild, heterogeneous populations?” is a central query propelling Karasov’s research. She begins asking this question by performing field surveys to assess the abundance and genotypes of pathogens infecting wild populations. Once she has determined which microbes are colonizing a host, she uses comparative and population genomics analyses to determine which plant and microbial genes are evolving in response to one another. These coevolutionary analyses pinpoint the molecular mechanisms that plants use to resist pathogens and that pathogens use to infect plants.

Through this interdisciplinary work that synthesizes field work with comparative genomics, microbiology and molecular biology Karasov and her colleagues are starting to get a picture of which genes and environmental factors are important for preventing pathogen spread.

During her post-doc studies at Max Planck she and her team sought to learn about pathogen adaptation to a diverse host by studying wild populations of the model plant Arabidopsis thaliana. Karasov found that Arabidopsis populations were largely resistant to being overtaken by single strain outbreaks of the bacterial pathogen Pseudomonas syringae. Genetic diversity in Arabidopsis populations seems to have forced the diversification of the pathogen population, and has prevented any one pathogen from causing widespread disease. This research also identified numerous rapidly evolving genes in the pathogen populations that may be evolving in response to changes in the host populations.

It’s the sort of question embedded in host-pathogen evolution and the maintenance of genetic diversity that will certainly inspire inquiries here in Salt Lake City and to possible solutions to the fast turn-around cycle of defense-counter-defense in crop yields essential to our own survival as a species.

Meanwhile, since arriving in the Beehive State, Karasov has been joined by another four-legged friend, a cattle dog adopted here in Utah, and together they have successfully made a home despite the epidemio-, geo- and meteorological challenges they’ve faced.