A TRUNCATED FRAGMENT OF HARPIN(PSS) INDUCES SYSTEMIC RESISTANCE TO XANTHOMONAS-CAMPESTRIS PV. ORYZAE IN RICE

Multiple isolates of Pseudomonas syringae induced a hypersensitive rea ction (HR) in tobacco and systemic resistance to Xanthomonas campestri s pv. oryzae in rice. These isolates all contain a DNA fragment homolo gous with the hrpZ gene of P. syringae pv. syringae 61. Harpin(Pss), e ncoded by the hrpZ gene, is postulated as a factor of these bacteria r esponsible for these activities. Harpin(Pss) partially digested by pro nase E are more active in inducing the hypersensitive reaction than th e intact protein in tobacco. According to the electrophoretogram of pr onase E partially digested samples, the enhanced HR activity results f rom the occurrence of some pronase E-tolerant fragments. Four 3' trunc ated hrpZ subclones were constructed, and one product of them, HTE3, c omprising the N-terminal 137 amino acids, appeared to be the strongest in inducing HR in tobacco, HTE3 could also induce systemic resistance to X. campestris pv. oryzae, although it did not induce a hypersensit ive-like response in rice seedlings. Thus harpin(Pss) appears to conta in an internal active fragment located in the amino terminal part, whi ch is sufficient for HR induction in tobacco and systemic-acquired res istance in rice. (C) 1997 Academic Press Limited.