A team of researchers from Michigan State University has discovered an unfortunate side effect of plants exposed to high humidity. The team found specific mechanics that bacteria use to take advantage of saturation in certain parts of the plasma membrane. These bacteria can quickly colonize an oversaturated plant, especially in humid weather conditions. The details are in a paper that was just published in the journal Nature.
Although high humidity and over-watering are known for leading to plant diseases, scientists have failed to figure out the connection between humidity and bacterial disease. Crops can be completely wiped out by devastating bacterial infections; understanding this link is critical for maintaining our global food sources.
Scientists exposed Arabidopsis thaliana plants, common scientific models in plant biology research, to strains of Pseudomonas syringae bacteria. This was the best way for the researchers to learn exactly how the bacteria were infecting the plants in changing environmental conditions. The first observations weren’t too surprising—the bacteria were suppressing the plants’ immune systems to infect the tissue. That still didn’t answer the question of why humidity seemed to result in more disease outbreaks.
The team found that when infecting plants, the P.syringae bacteria used the apoplast as a point of entry. The apoplast is the space right outside the plasma membrane of a plant cell. This area is necessary for the diffusion and transportation of important resources. As bacteria entered the apoplast during the experiment, they released special proteins that filled the area with water. In other words, the bacteria were saturating the apoplast to make it better suited for bacterial colonization and the spread of disease. Releasing the protein wasn’t enough on its own to accomplish this, however, and the researchers found that P.syringae bacteria were collecting water from the air. This means that humid conditions make it much easier for certain bacteria to colonize and infect plants.
The team’s findings may help agriculturists prevent serious disease outbreaks. By understanding how humidity and other environmental conditions change the risk of infection, scientists can develop new ways to tackle crop diseases.
Xin et al. Bacteria establish an aqueous living space in plants crucial for virulence. Nature (2016).