The Web of Life (79-9) Damn Spots

 Damn Spots

Phytopathogens can manipulate plant hormone signaling to access nutrients and counteract defense responses. ~ Chinese botanist Xiao-yu Zheng et al

Pseudomonas syringae is bacterial pathogen that produces brown leaf spots in over 50 different plants. The brown spot bacterium is a biotroph but fools a plant into thinking it is a nectrotroph.

Pseudomonas produces coronatine, which mimics jasmonic acid, and initiates a cascade of molecular activity that mimics a necrotrophic invasion. The plant responds by lowering salicylic acid production to keep the cell alive. Normally, salicylic acid is involved in closing stomata, and acts an essential signal for the cell-killing defense that would be most effective against a biotroph.

By confusing the plant and jamming signals, Pseudomonas keeps the stomata open for further infestation. Meanwhile, it has free rein to reproduce in extracellular spaces.