University of Colorado Boulder-led sunflower research shows their genes are linked to the abundance of bacteria linked to resistance to one of the pathogens that causes white mold
Sunflowers are not only a symbol of summer beauty but also economically important, being the fourth most important oilseed crop in the world, and new research suggests that some bacteria may help protect the crop from the ravages of white mold.
They can harvest a variety of products, including seeds and oil, and consumer demand has increased significantly in recent years. Researchers note that sunflowers may also contribute to climate resilience because they can adapt to various weather conditions and sunflower sprouts contain nutrients that may promote human health.
Unfortunately, like many other plants, sunflowers are susceptible to disease, resulting in severe crop losses.For example, white mold, caused by a fungal pathogen Sclerotinia, resulting in an average annual loss of more than 1% of sunflower crops. It also affects beans, eggplants, lettuce, peanuts, potatoes and soybeans, in some cases destroying 100% of the crop.
Nolan Cain, associate professor of ecology and evolutionary biology at the University of Colorado Boulder, and his research colleagues found that some bacteria in the soil around the roots of sunflowers may help protect them from white mold infection.
While approaches to controlling diseases such as white mold often focus on plant genetics, a recent study published in the journal Plant Genetics molecular ecology Researchers led by the University of Colorado Boulder have shown that the microbial communities surrounding plant roots also play an important role, and that plant genetic variation does in fact affect the associated microbiome.
Field and greenhouse experiments
The study included a greenhouse study and a field experiment in which the researchers extracted and sequenced DNA from different varieties of sunflowers. Twenty plants of each sunflower variety were grown in a field that the researchers expected contained microorganisms hostile to sunflowers. Sclerotinia pathogen. Some plants are infected and some are not, which is necessary to differentiate between microorganisms relevant to the study and those that exploit virus-induced tissue death. Sclerotinia.
In the greenhouse experiments, sunflowers were grown in soil in the same environment as the field experiments, half of which was sterilized to remove any microorganisms. The plants were infected and their resistance to disease assessed, allowing the researchers to determine the importance of the microbes to the outcomes experienced by different varieties of sunflowers in field experiments. If sunflowers grown in sterile soil have less disease resistance, it means that microorganisms confer disease resistance on the plants.
Researchers learned that 42 microbial species were associated with disease resistance. Greenhouse experiments showed that these microorganisms are important for plant disease resistance, as sunflowers in sterile soil died 19 days earlier than similar sunflowers. Next, the abundance of the main microorganisms was related to the genetic characteristics of the different plants, and the researchers found that certain genes corresponded to increased microbial abundance.
The researchers concluded that this all suggests that different varieties of sunflowers have been genetically modified to increase the number of beneficial microorganisms in nearby soil, making them more resistant to white mold. Since the link between plants and microorganisms is genetic and therefore heritable, this resistance can be developed through methods such as breeding.
Microbial and plant disease resistance
Nolan Kane, an associate professor of ecology and evolutionary biology at the University of Colorado Boulder and a renowned sunflower researcher, said that before this study, it was unclear how much influence microbial communities had on plant disease resistance.
He said there are indeed some documented cases where this is important, but for most pathogens the plants have the right allele on this gene and they become resistant to the pathogen if they Without the correct alleles, they are susceptible.
(Humans) have a very sophisticated immune system that recognizes new proteins all the time. Plants have very different immune systems, which are often simplified to just a single gene that detects pathogens. If the pathogen protein is a detectable version of the gene, the plant becomes resistant, but without the right match, the plant becomes sensitive.
Unlike the human immune system, plant immune systems do not keep track of every microbe they fight. Instead, they use specialized receptors to recognize molecular patterns associated with disease. Each type of receptor can only interact with specifically shaped molecules, which fit together like matching puzzle pieces. Once this contact occurs, the receptors signal a defense response.
White mold, caused by a fungal pathogen Sclerotinia, resulting in an average annual loss of more than 1% of sunflower crops. (Photo: National Sunflower Association)
Take the sunflowers studied by Kane and his fellow researchers, at least in Sclerotinia, things are more complicated. “In this case, we do think the microbiome or some other environmental component may play an important role,” Kane said. The researchers found that four bacteria were closely associated with sunflower resistance to fungal pathogens, suggesting their hunch was correct.
However, Kane said there are many microbes related to each other, meaning the effect could be a result of the entire community and not just the four bacteria, which are known as operational taxonomic units (OTUs).
Kane continued, “The four bacteria we highlighted are most closely related to pathogen resistance, and when we controlled for these four bacteria, none of the other associated OTUs were associated with disease, although the main four bacteria may not improve disease resistance alone.” sex, because many of these microorganisms do not grow well on their own or behave differently when cultured alone.
Plant/microbe symbiosis
Researchers found that the more of these four bacteria in the soil around plants, the better they were able to fight off Sclerotinia. So, how do plants use these bacteria, and what does this have to do with plant genetics?
It turns out that plants can cultivate useful microbial communities in the area of soil around their roots, known as the rhizosphere.
In general, Kane explains, plants can secrete compounds that inhibit the growth of certain microorganisms or promote their growth. Photosynthesis is the process by which plants convert light into usable energy, producing large amounts of carbohydrate molecules such as sugar and starch. For this reason, Kane said, many of their interactions with microbes involve sugars or carbohydrates provided by plants, which benefit by getting nitrogen or other things they need.
Plants have similar symbiotic relationships with fungi, and they can benefit from a boost. Nitrogen is just one example of the benefits plants get from symbiotic relationships: In the studies we’ve done, we don’t know if it’s necessarily the same mechanism, Kane says, but it’s likely that there’s some kind of root exudate that’s shaping the microbiome. . This is one of the key mechanisms used by plants.
The way plants interact with rhizosphere microbes depends on their genes. As a result, the researchers were able to link four bacteria to specific parts of the sunflower’s genetic code.
Association with microorganisms
The study had other important findings.Results showed that 4 out of 40 sunflower samples studied were resistant Sclerotinia Even without the protection of beneficial bacteria. They did perform worse in sterilized soil than in soil with bacteria, but significantly better than the other samples.
Researchers at the University of Colorado Boulder have discovered that sunflowers can cultivate useful microbial communities in the soil zone around their roots.
It could be some ability to respond to pathogens in a protective way, Kane said. We do not yet know whether this is a useful breeding goal because of possible trade-offs, or whether it may have limited or no protective effect under normal conditions. Still, it does suggest that the whole story isn’t just about microbes. There’s an important component, even if it’s smaller, that has to do with inherent plant genetics.
This study raises further questions about the costs and benefits of microbial symbiosis, the molecular mechanisms of symbiotic changes, and the importance of interactions between genotype and environmental factors. Kane said he and his research colleagues are studying some of these strains in more diverse environments across the United States and trying to determine whether these microbial associations are common across a wide range of environments or whether they are specific to one environment.
Because these studies are conducted in farmers’ fields, the plants examined are not exposed to pathogens. Instead, researchers are focusing on plant-microbe connections, Kane said.
Likewise, Kane said it’s really exciting to see these genetic effects on so many different microbes in the same environment, because it suggests the sunflowers we used in this study have some interesting variations that may be related to our related to various characteristics of the study.
Many crops lose some of their microbial associations through breeding, but this is not a problem for the research community, making it potentially valuable for future research, Kane said.
Still, recently published research provides ideas on how to exploit microbial associations to protect plants. The most straightforward approach is to selectively breed plants for genes that correspond to increased abundance of beneficial microorganisms in the rhizosphere.
Kane explained that in addition to breeding, different agricultural and environmental practices can promote beneficial communities or suppress harmful ones. It is also important to apply useful microorganisms to the field if they do not yet exist. Kane said it could be a combination of more than one different thing. Some biotech companies are already working on mixtures of microbes that could be beneficial to certain crops, which could be applied in fields or coated on plant seeds.
This research could certainly help with sunflower breeding, Kane concluded, but it could also help us understand how to breed other species more efficiently, as well as some basic science, including not just how plants interact with their environment, but how the entire community beneath the soil works. interaction.
Cairns’ co-investigators include Cloe Pogoda, Kyle Keepers, Stephen Reinert, Ziv Attia, Jason Corwin, Erin Collier-zans and Alisha Quandt of the University of Colorado Boulder’s Department of Ecology and Evolutionary Biology; and Zahirul Talukder, Brian Smart, Kennedy Money , William Underwood, Thomas Gulya and Brent Hulke.
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