SUPEROXIDE-DISMUTASE - A DIFFERENTIATION PROTEIN EXPRESSED IN UROMYCES GERMLINGS DURING EARLY APPRESSORIUM DEVELOPMENT

Germlings of the bean rust fungus Uromyces appendiculatus detect penet ration sites on the surface of the host leaf by thigmosensing topograp hical features. Within 2-4 min after the apex of a urediospore germ tu be encounters the cuticular lip of a stomate, the germling ceases pola rized growth and begins to swell over the aperture. The mechanism by w hich the cells detect topographical signals is not understood; however , previous experiments indicated that the initiation process does not involve de novo gene expression. In order to detect posttranslational modifications, the protein profiles of induced and noninduced germling s were compared at the earliest stages of appressorium formation, and a 21-MDa differentiation protein was identified by a shift in isoelect ric point. The N-terminal amino acid sequence exhibited homology with superoxide dismutase(SOD), and antibodies to a synthetic peptide fragm ent of the respective sequence recognized cooper/zinc isozymes of SOD in electroblots of native gels. Electroelution of the active enzyme ba nds and separation by SDS-PAGE indicated that the 21-kDa protein is a component of a tetrameric 85-kDa SOD. (C) 1995 Academic Press, Inc.