P syringae action elucidated
Researchers from the UK’s Imperial College (London) have elucidated the molecular mechanism used by the bacterial disease, Pseudomonas syringae, to trigger plant infection. In tomatoes, where it causes bacterial speck, it uses a pair of two very similar genes, HrpR and HrpS (HrpRS), which have evolved as a result of gene duplication. The genes work in tandem to launch the infection process that eventually kills the plant's cells. The researchers found that the HrpRS pair control the production of pili, which are needle-like structures through which bacteria secrete proteins that repress plant cell immune responses. Pili are only produced once bacteria are inside a plant cell. Pili development, and thus infection, cannot proceed effectively without both genes being active.