A truncated fragment of harpinPssinduces systemic resistance toXanthomonas campestrispv.oryzaein rice

Abstract

Multiple isolates ofPseudomonas syringaeinduced a hypersensitive reaction (HR) in tobacco and systemic resistance toXanthomonas campestrispv.oryzaein rice. These isolates all contain a DNA fragment homologous with thehrpZgene ofP. syringaepv.syringae61. HarpinPss, encoded by thehrpZgene, is postulated as a factor of these bacteria responsible for these activities. HarpinPsspartially digested by pronase E are more active in inducing the hypersensitive reaction than the intact protein in tobacco. According to the electrophoretogram of pronase E partially digested samples, the enhanced HR activity results from the occurrence of some pronase E-tolerant fragments. Four 3′ truncatedhrpZsubclones were constructed, and one product of them, HTE3, comprising the N-terminal 137 amino acids, appeared to be the strongest in inducing HR in tobacco, HTE3 could also induce systemic resistance toX. campestrispv.oryzae, although it did not induce a hypersensitive-like response in rice seedlings. Thus harpinPssappears to contain an internal active fragment located in the amino terminal part, which is sufficient for HR induction in tobacco and systemic-acquired resistance in rice.