rightVast vineyards dotted with carefully tended vines fill the air with sweet, fruity aromas that are typical of America’s booming wine industry. In the 1800s, however, these lands painted a different picture, with Pierce’s disease (PD) ravaging the vines, causing leaves to wilt and fruit to wither.1
caused by bacteria Xylella fastidiosaPD was first notified in California in 1884.2 Since then, the disease has been found across the globe, destroying vines and causing economic losses. Researchers estimate the disease costs more than $100 million in California alone.3 The widespread damage caused by PD has prompted the research community to identify the origins of the pathogen and determine how it spreads across continents.
Herbaria are valuable repositories of ancient plant specimens, providing well-preserved specimens that provide a unique window into historical ecosystems, plant evolution, and the spread of pathogens over time.
UC Davis Plant Diversity Center Herbarium
Now, after isolating the bacterium from a 120-year-old grapevine, scientists have reconstructed the history of Parkinson’s disease, including its arrival in California and its mode of spread.4 Their findings were published in modern biologyalso reveals a key moment in the history of bacterial evolution.
“The biogeography of this pathogen is That’s important because new outbreaks are constantly occurring, leading to epidemics around the world, she said. Understanding the history of pathogens can help researchers understand the context of disease outbreaks and reveal the evolutionary adaptations that led to them.
To delve deeper into the pathogen’s history, the researchers obtained historic grapevine specimens from the UC Davis herbarium. Of the 10 diseased cuttings they found, one was infected X. X. fastidiosa.
To isolate DNA from samples, researchers had to work in ultra-clean conditions to avoid cross-contamination with modern samples, recalls study co-author Monica Donegan, a graduate student in Almeida’s lab. After filtering the sequencing reads and extracting those that map to modern X. X. fastidiosa After analyzing the genome, the team was left with a pile of short fragments typical of ancient DNA, confirming that there was no cross-contamination in modern samples.
Next, the team stitched the pieces together to assemble the ancient piece from scratch. X. X. fastidiosa genome. Researchers use computational phylogenetic tools to compare historical genomes X. X. fastidiosa These include 330 of the latest strains collected from plants in the United States, Costa Rica, Spain, Taiwan and Mexico. This helped the team build a detailed phylogenetic tree charting the pathogen’s evolutionary lineage.
Phylogenetic analysis showed that the herbarium strains were closely related to newer strains from California and the eastern United States, suggesting a common ancestral origin. However, not all X. X. fastidiosa Strains found in California grapevines share this common ancestor, as some of them are more similar to strains from the eastern, central and Spanish United States. These findings suggest that in California, the disease is caused by multiple introductions of the pathogen.
After determining that multiple entries exist X. X. fastidiosa After entering U.S. plants, researchers set out to determine when the pathogen first entered the country. By measuring the mutation rate of the pathogen’s DNA over time, the researchers estimated that all X. X. fastidiosa The strains in the United States share a common ancestor dating back to approximately 1741, 35 years before the Declaration of Independence was written, and 150 years before PD was first recorded in California.
Looking for clues about evolution X. X. fastidiosaAlexandra Kahn (left) and Monica Donegan (right) collect ancient DNA samples from plants preserved in the herbarium.
Matthew Burciaga, University of California, Berkeley
“That actually surprised us a little bit because we thought the sample we had (because it’s from 1906) would be the ancestor of everything in California,” Donegan said. “Adding just one herbarium from 1906 pushes the date of introduction back. This emphasizes the power of adding these herbariums and ancient samples to these studies.
“This is a good study,” said Michael Martin, an evolutionary genomics researcher at the Norwegian University of Science and Technology who was not involved in the study. Although researchers have sequenced ancient plant pathogens before, this study is noteworthy because the team performed a complete de novo assembly X. X. fastidiosahe pointed out.
However, he was not surprised that the addition of the 1906 sample pushed the pathogen’s estimated introduction date back. “Predictions of introduction times are all based on these phylogenetic trees, and the dates you get for different parts of the tree depend directly on the samples you include,” he said.
The team hopes to collect more samples to get a clearer picture of the pathogen’s entry and eventual spread. Since most of the plant samples came from California, the researchers aimed to diversify and sample in other areas of the country. “We can try to really [fill] There are gaps in our data collection,” Kahn said.
