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Understanding cooperation and conflict in plant symbionts

Understanding cooperation and conflict in plant symbiotes

Medicago truncatula plants in the greenhouse were infected with Sinorhizobium meliloti. Credit: Rebecca Batstone

The traditional idea of ​​symbiosis – long-term interactions between two organisms – is that the participants mutually benefit from each other. However, researchers have debated whether the interests of the symbionts always match the hosts they inhabit, or whether genes that benefit symbionts can be at the expense of their hosts. A new study explores this question through genomic sequencing and infecting plant hosts with their microbial symbionts.

“It has become clear that the health of crops and our own health is determined by the microbes we interact with. For example, in agriculture there is a big movement to try to develop microbes to make happier plants,” said Katy Heath (IGOH ), an associate professor of plant biology. “Our approach is a little different because we can measure all of the genomic variations in a natural population of symbionts that have been interacting with their host for a long time to see what genes do in nature.”

“There’s the idea that microbes that interact with humans or plants are automatically beneficial because they’ve been living with them for a very long time,” said Rebecca Batstone, a former postdoctoral researcher at the Carl R. Woese Institute for Genomic Biology. “However, a lot of work has shown that the interests of the symbionts do not always align with those of the host they inhabit. We wanted to ask at the genome level how much alignment there is between hosts and symbionts versus how much conflict.”

In their study, the researchers examined naturally occurring 191 strains of the microbial symbiote Sinorhizobium meliloti, combined with its host Medicago truncatula, a clover-like plant native to the Mediterranean region. The microbe resides in the root nodules of the plant and supplies it with nitrogen. The group matched each microbial strain to an individual plant and also used a mix of different strains and infected the same plant, a competitive situation that often occurs in nature.

“In our experiments, we measured how well the plant is doing with the specific microbial strain,” Batstone said. “In addition to measuring plant growth, we also looked at microbial fitness by counting the number of nodules that were packed with these microbes and measuring the nodule size.”

The researchers also sequenced the genomes of the microbial strains, and using a technique called genome-wide association, they were able to compare which bacterial genes are associated with plant growth.

“If there is an association, for example a gene of interest is strongly associated with plant growth, then it is an indication that the gene may be important for controlling that trait,” Batstone said.

When they compared how many symbiote genes matched the host’s interest, the researchers found that nearly 80% of the genes they identified appeared to be associated with alignment.

“In competitive environments, you would expect that there will be a disconnect between the interests of the host and symbionts, because the symbionts are also competing with each other,” Batstone said. “This is a striking result because it shows that while the symbionts don’t evolve to help their hosts, it often pays to be beneficial.”

While they’ve worked with more than 2,000 plants, the group would like to look at more hosts to see if this trend still holds true for a larger sample of plant species. They also want to test these interactions under different environmental conditions.

“We did everything under low nitrogen conditions because the plants get nitrogen from their symbionts. You can imagine if you add nitrogen to the system, you might see more conflict,” Batstone said.

Biologists shed light on mystery of how microbes evolve and affect hosts

More information:
Rebecca T. Batstone et al, Phenotypic and genomic signatures of interspecies cooperation and conflict in naturally occurring isolates of a model plant symbiont, Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.0477

Provided by the University of Illinois at Urbana-Champaign

Quote: Understanding cooperation and conflict in plant symbiotes (2022, August 3), retrieved August 3, 2022 from https://phys.org/news/2022-08-cooperation-conflict-symbionts.html

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