A mitogen-activated-protein kinase from soybean is activated by a pathogen and novel functional analogs of salicylic acid

Treatment of soybean cells (Glycine max L. Merr, cultivar Williams 82) with salicylic acid (SA) rapidly activates a protein kinase within 2–5 min. The activation is dose dependent and transient, decaying to basal activity within 30 min. This kinase is a member of the mitogen-activated protein kinases (MAPK) based on the molecular weight of 48 kDa, the ability to phosphorylate myelin basic protein and specific immuno-precipitation by anti-MAPK antibodies. The soybean MAPK is also activated by low concentration of functional analogs of salicylic acid, including flufenamic acid, LY-171,883 and WY-14,643, which complement a SA dependent cell death program in a soybean–Pseudomonas interaction. Inoculation of soybean cells with Pseudomonas syringae pv. glycinea bacteria in the presence of SA leads to a biphasic activation of the MAPK. The second activity phase occurs at 40–50 min after addition of the bacteria and suggests an exchange of a bacterial signal or metabolite with the plant cells resulting in the second activation of the MAPK.