300,000 year standoff could be key to crop pathogen control

©Max Planck Institute for Developmental Biology

Tübingen, 17 July 2018. Researchers in the laboratory of Detlef Weigel at the Max Planck Institute for Developmental Biology discovered a feud going back 300,000 years by studying a common pathogenic bacterium and one of the wild plants it infects. The new findings underscore how in natural ecosystems, the genetic diversity of both plant host and pathogen is greater, and the ongoing struggle between them more evenly matched than in agriculture.

 The scientists were curious how pathogens evolve in a natural ecosystem, without selective breeding. To this end, they visited for three years each fall and spring local places near Tübingen where mouse-eared cress regularly grows, and collected leaves. From these leaves, they isolated Pseudomonas, a widespread occurring bacterium, and sequenced the genomes of well over a thousand different bacteria strains. Their results suggest it is not only the plant that has greater diversity in the natural environment, but the pathogen too. These findings lead some to believe that it is the diversity in plants and the surrounding ecosystem that protects against the threat of any one single microbe strain. Understanding this diversity could boost efforts to combat pathogenic desolation of crop populations.

One common Pseudomonas lineage was found everywhere the team took samples. This single lineage was highly diverse and extremely effective at colonizing most of the plants. It was also much older than expected - not a few decades, but several hundred thousand years. In contrast to agricultural settings, in the natural ecosystem not one single strain had been able to take over the cress, even though they had been around for many millennia.

The study, which has been produced in collaboration with the laboratory of Eric Kemen at the University of Tübingen and was recently published in Cell Host and Microbe, suggests a fine tuned balance between host and pathogen with no single lineage totally dominating or overtaking plants. As each adapts the other responds, resulting in a balanced state over an extremely long time.

Talia Karasov of the Max Planck Institute for Developmental Biology says: “We were amazed by the sheer magnitude of diversity that we saw even in a small geographic area and this told us clearly that we are not seeing the same dynamics as in agriculture. Our prior understanding of plant and pathogen coevolution was premised on a single strain evolving to a single host and sweeping through a population. Now we want to figure out how the diversity of both the plant and surrounding microbes are involved in enabling or stopping a pathogen invading an environment.”

The original publication can be found here: http://www.cell.com/cell-host-microbe/fulltext/S1931-3128(18)30323-8