Identification of soybean elicitation competency factor, CF-1, as the soybean Kunitz trypsin inhibitor

The soybean defence responses that occur in cells immediately adjacent (proximal) to the hypersensitive response (HR) can he induced by the cell wall glucan elicitor (WGE) from Phytophthora sojae, but in some cultivars only in cells that have been pre-conditioned by endogenous competency factors associated with wounded or HR-dying cells. Competency factor, CF-1, causes a general amplification of phenylpropanoid responses to elicitor and greatly enhances the phenolic polymer response to elicitor. CF-1 activity, which is heat-labile and associated with it low speed centrifugal pellet of soybean tissues, call be partially mimicked by reduced glutathione (GSH). Here it is reported that GSH releases CF-1 activity into intercellular washing fluids, suggesting it is associated with the apoplast. Likewise, GSH can be used to enrich CF-1 activity greatly in extracts from low speed pellets. This enrichment allowed the purification of CF-1 to near homogeneity and its subjection to mass spectral and sequence analysis. CF-1 was identified as the soybean Kunitz trypsin inhibitor (SKTI). Although plant protease inhibitors have been implicated in insect and pathogen resistance, to the authors' knowledge this is the first suggestion of a regulatory role in activation of cellular defence responses. Protease inhibitors play a role in many signaling processes in eukaryotic systems, and SKTI has intriguing three-dimensional homologies to interleukin 1-alpha and 1-beta and fibroblast growth factor. (C) 2001 Academic Press.