Scientists uncover “gene transfer agent” in Nigerian plant bacterial strain
Researchers affiliated with Nigerian and United States universities said they identified “gene transfer agents” (GTAs) in bacteria that cause plant diseases. These genetic elements help drive the evolution (genetic changes) of the bacteria over time, so understanding more about them may ultimately help scientists better manage the plant diseases they cause.
Plant pathogenic bacteria are tiny microorganisms that cause disease in the plants they infect. Like all living organisms, the instructions that determine the structure and function of these bacteria are coded for within their genes, and small changes in this genetic code is what allows it to adapt to new environments or challenges over time.
Some bacteria use “gene transfer agents” (GTAs) to introduce such genetic changes by transferring genetic material between one another (as opposed to transferring its genetic material to its offspring).
Researchers had previously noticed a pattern of genetic changes similar to those caused by GTAs in a plant disease-causing Xanthomonas strain from Nigeria, and decided to investigate further.
They specifically wanted to study more about the relationship between this Nigerian strain and other strains found elsewhere.
Through genetic analyses they indeed confirmed that this strain from Nigeria contains a GTA. They also found GTA clusters in other Xanthomonas, as well as species of Agrobacterium and Pantoea.
However, many of the other common plant disease-causing bacteria they investigated did not contain GTAs.
The researchers said bacteria with GTAs were more likely to change their genetic makeup over time than those without.
They cannot say why only certain bacteria have GTAs, but suspect it may help those that have it to infect their host. They also speculate that perhaps these bacteria only recently gained GTA elements.
Xanthomonas causes bacterial spots on leaves and fruit, leading to crop losses. Understanding how this strain from Nigeria evolves and infects plants with the help of GTAs could help researchers understand how to manage this and other plant diseases in future.
Background Gene transfer agents (GTAs) are phage-like mediators of gene transfer in bacterial species. Typically, strains of a bacteria species which have GTA shows more recombination than strains without GTAs. GTA-mediated gene transfer activity has been shown for few bacteria, with Rhodobacter capsulatus being the prototypical GTA. GTA have not been previously studied in plant pathogenic bacteria. A recent study inferring recombination in strains of the bacterial spot xanthomonads identified a Nigerian lineage which showed unusual recombination background. We initially set out to understand genomic drivers of recombination in this genome by focusing on mobile genetic elements.
Results We identified a unique cluster which was present in the Nigerian strain but absent in other sequenced strains of bacterial spot xanthomonads. The protein sequence of a gene within this cluster contained the GTA_TIM domain that is present in bacteria with GTA. We identified GTA clusters in other Xanthomonas species as well as species of Agrobacterium and Pantoea. Recombination analyses showed that generally, strains of Xanthomonas with GTA have more inferred recombination events than strains without GTA, which could lead to genome divergence.
Conclusion This study identified GTA clusters in species of the plant pathogen genera Xanthomonas, Agrobacterium and Pantoea which we have named XpGTA, AgGTA andPaGTA respectively. Our recombination analyses suggest that Xanthomonas strains with GTA generally have more inferred recombination events than strains without GTA. The study is important in understanding the drivers of evolution of bacterial plant pathogens.
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