SALICYLIC-ACID INTERFERES WITH TOBACCO MOSAIC-VIRUS REPLICATION VIA ANOVEL SALICYLHYDROXAMIC ACID-SENSITIVE MECHANISM

Salicylic acid (SA) induces resistance to all plant pathogens, includi ng bacteria, fungi, and viruses, but the mechanism by which SA engende rs resistance to viruses is not known. Pretreatment of tobacco mosaic virus (TMV)-susceptible (nn genotype) tobacco tissue with SA reduced t he levels of viral RNAs and viral coat protein accumulating after inoc ulation with TMV. Viral RNAs were not affected equally, suggesting tha t SA treatment interferes with TMV replication. Salicylhydroxamic acid (SHAM), an inhibitor of the mitochondrial alternative oxidase, antago nized both SA-induced resistance to TMV in nn genotype plants and SA-i nduced acquired resistance in resistant (NN genotype) tobacco. SHAM di d not inhibit induction of the PR-1 pathogenesis-related protein or in duction of resistance to Erwinia carotovora or Botrytis cinerea by SA. This indicates that SA induces resistance to TMV via a novel SHAM-sen sitive signal transduction pathway (potentially involving alternative oxidase), which is distinct from that leading to resistance to bacteri a and fungi.