Cloning, expression and characterization of protein elicitors from the soyabean pathogenic fungus Phytophthora sojae

The oomycete Phytophthora sojae is a severe pathogen of soybean. Several re sistance genes against races of P. sojae exist in soybean but the nature of corresponding avirulence genes is unknown. Clones encoding four different isoforms of a protein elicitor from P. sojae (sojein 1-4) belonging to the class of acidic alpha-elicitins have been isolated. These 98 amino acid pro teins show high homology to elicitins from other Phytophthora species. The different sojein isoforms were expressed in Escherichia coli as His-tagged fusion proteins. Purified sojein as well as recombinant sojein isoforms ind uce hypersensitive reaction (HR)-like lesions in tobacco but are not active as race-specific elicitors in soybean. However all sojein isoforms induce defence-related genes like those encoding phenylalanine ammonia lyase, glut athione-S-transferase and chalcone synthase in tobacco and soybean plants a nd cell cultures. It is concluded that sojeins contribute to the induction of defence responses but that they are not involved in race specific recogn ition of the P. sojae races by soybean plants.