Purification and characterization of a soluble salicylic acid-binding protein from tobacco.
Previously, we identified a soluble salicylic acid (SA)-binding protein (SABP) in tobacco whose properties suggest that it may play a role in transmitting the SA signal during plant defense responses. This SA-binding activity has been purified 250-fold by conventional chromatography and was found to copurify with a 280-kDa protein. Monoclonal antibodies capable of immunoprecipitating the SA-binding activity also immunoprecipitated the 280-kDa protein, indicating that it was responsible for binding SA. These antibodies also recognized the 280-kDa protein in immunoblots of the partially purified SABP fraction or the crude extract. However, when the crude extract was prepared in the presence of antioxidants, only a 57-kDa protein was recognized. Since the SABP has a native molecular mass of 240 kDa, it appears that the SABP is a complex which contains a 57-kDa subunit and perhaps one or more additional proteins which are covalently crosslinked in the absence of antioxidants. The ability of a variety of phenolic compounds to compete with SA for binding to the SABP was both qualitatively and quantitatively correlated with their biological activity in inducing defense-related genes. Moreover, the inducibility of the pathogenesis-related (PR)-1 genes by SA was proportional to the abundance of the SABP in different organs. These correlations are consistent with a role for the SABP in perceiving and transducing the SA signal in plant defense.
Chen
Z
Z
Waksman Institute, Rutgers, State University of New Jersey, Piscataway 08855-0759.
Ricigliano
J W
JW
Klessig
D F
DF
D000911:Antibodies, Monoclonal / Q000276:immunology; D005786:Gene Expression Regulation; D017343:Genes, Plant; D010935:Plant Diseases; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification*; D010947:Plants, Toxic; D011233:Precipitin Tests; D012459:Salicylates / Q000378:metabolism*; D015398:Signal Transduction; D014026:Nicotiana / Q000502:physiology*
D000911:Antibodies, Monoclonal; D010940:Plant Proteins; D012459:Salicylates; C053376:pathogenesis-related proteins, plant