As hard as we fight against plant pathogens, we have to be aware that those pathogens are doing what they can to fight us. One such microbe, Ralstonia solanacearum, enters roots through wounds or natural openings and chokes off the water-transport system of a plant. The result is that the plant — commonly tobacco, tomatoes, and potatoes, among others — wilts and dies.
R. solanacearum has been the focus of intense research, the latest coming from Caitilyn Allen, from the University of Wisconsin, and published last month in the journal PLOS Pathogens. Allen’s team looked at the interaction between R. solanacearum and the specialized border cells at the outer surface of plant roots that fight off pathogenic microbes. Plants go on the defensive around this pathogen, responding by releasing DNA, thereby forming sticky traps that entangle the bacteria. The researchers noted that about 25 percent of the entangled bacteria were killed in the traps. “The anti-bacterial activity depended both on the presence of extra-cellular DNA and of histone H4, a DNA-associated protein present in plant and animal cells,” according to the news release on the study.
The researchers were trying to identify which specific pathogen signals trigger the extra-cellular trap response in the root. Basically, they wanted to know why will a plant root tries to fend off R. solanacearum yet doesn’t go after another microbe with the same defensive intensity. This was done by sending mutated versions of R. solanacearum against a plant root to see what differences triggered the root’s defenses. It was also discovered that plant pathogens use the nuclease enzyme to escape the extracellular DNA traps generated by host root border cells.
The study, of course, didn’t crown a long-term winner in this struggle. What it did do is give science a competitive edge: Understanding the host-pathogen interactions at the plant root might help in breeding or engineering disease-resistant plant variants.
Images courtesy of Tran et al.