Virus-induced synthesis of messenger RNAs for precursors of pathogenesis-related proteins in tobacco

Infection of Samsun NN tobacco with tobacco mosaic virus (TMV) induces a number of host-encoded, so-called pathogenesis-related (PR-) proteins, which are found in the intercellular space of the leaf and are associated with induced resistance. By immunoprecipitation of their in vitro translation products we were able to detect the mRNAs corresponding to a number of PR-proteins in TMV-infected tobacco, but not in healthy plants. Analysis by the Northern blot technique using cloned cDNA of PR1-mRNAs as probe showed that the mRNAs for the closely related proteins PR1a, 1b and 1c occur at a low level in healthy tobacco; upon TMV infection this level is increased > 100-fold. The PR1-specific probe did no hybridize to mRNAs corresponding to other PR-proteins. Sequencing of the 5'-terminal region of PR1-mRNAs showed that PR1-proteins are derived from precursors by removal of an N-terminal signal peptide of 30 amino acids.