Plant Molecular Biology 21: 985-992, 1993. © 1993 Kluwer Academic Publishers. Printed in Belgium. 985 Tobacco proteinase inhibitor I genes are locally, but not systemically induced by stress Huub J.M. Linthorst, Frans Th. Brederode, Chris van der Does and John F. Bol Institute of Molecular Plant Sciences, Department of Biochemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, Netherlands Received 3 September 1992; accepted in revised form 20 December 1992 Key words: pathogenesis-related proteins, signal transduction, wound induction Abstract A cDNA library of tobacco mosaic virus (TMV)-infected tobacco was screened with polymerase chain reaction products obtained using a degenerate primer corresponding to proteinase inhibitor I (PI-I) of tomato and potato. The resulting clones encoded two highly similar, putative tobacco PI-I proteins, indicating that both genes identified in tobacco are probably expressed. The tobacco PI-I's were ap- proximately 50 ~o identical to wound-inducible potato and tomato PI-I and 80 ~o identical to an ethylene- regulated tomato PI-I. Northern blot analyses indicated that healthy tobacco leaf contains only minor amounts of PI-I mRNA, and that the inhibitor genes are induced by TMV infection, salicylate treatment, ethephon spraying, UV light irradiation and wounding. The results indicate that the tobacco PI-I genes are coordinately expressed with the genes for the basic pathogenesis-related proteins. Contrary to PI-I genes of tomato and potato, wound induction of the tobacco genes occurs only locally; the upper, un- wounded leaves do not show any wound-induced PI-I gene expression. Introduction Plants respond to stress conditions with the in- duced expression of a large number of genes. In recent years, we and others have characterized several classes of genes encoding so-called patho- genesis-related (PR) proteins, which are induced upon necrotizing infection of tobacco with to- bacco mosaic virus (TMV) and other pathogens. Similar PR proteins are induced in many differ- ent plant species upon infection with viruses, vi- roids, fungi and bacteria [for a review see 10]. The tobacco PR proteins can be divided in groups of homologous acidic and basic counter- parts. Each group contains five sets of proteins. The acidic PR proteins all accumulate in the ex- tracellular space of the leaf, whereas the basic proteins are targeted to the vacuole. The enzy- matic or biological activity of several of these pro- teins suggests that they are involved in the in- duced resistance of the plant to pathogen attack [10,21]. Recently, we showed that acidic and basic PR proteins display different stress induc- tion patterns; the most distinct difference being The nucleotide sequence data reported will appear in the EMBL Nucleotide Sequence Database under the accession numbers Z12619 (PII-4) and Z12623 (PII-3).