TOBACCO PROTEINASE INHIBITOR-I GENES ARE LOCALLY, BUT NOT SYSTEMICALLY INDUCED BY STRESS

A cDNA library of tobacco mosaic virus (TMV)-infected tobacco was scre ened with polymerase chain reaction products obtained using a degenera te primer corresponding to proteinase inhibitor I (PI-I) of tomato and potato. The resulting clones encoded two highly similar, putative tob acco PI-I proteins, indicating that both genes identified in tobacco a re probably expressed. The tobacco PI-I's were approximately 50 % iden tical to wound-inducible potato and tomato PI-I and 80 % identical to an ethylene-regulated tomato PI-I. Northern blot analyses indicated th at healthy tobacco leaf contains only minor amounts of PI-I mRNA, and that the inhibitor genes are induced by TMV infection, salicylate trea tment, ethephon spraying, UV light irradiation and wounding. The resul ts indicate that the tobacco PI-I genes are coordinately expressed wit h the genes for the basic pathogenesis-related proteins. Contrary to P I-I genes of tomato and potato, wound induction of the tobacco genes o ccurs only locally; the upper, unwounded leaves do not show any wound- induced PI-I gene expression.