A hot pepper cDNA encoding a pathogenesis-related protein 4 is induced during the resistance response to tobacco mosaic virus

Hot pepper (Capsicum annuum) plants exhibit a hypersensitive response (HR) against infection by many tobamoviruses. A clone (CaPR-4 encoding a putativ e pathogenesis-related protein 4 was isolated by differential screening of a cDNA library prepared from resistant pepper plant leaves inoculated with tobacco mosaic virus (TMV) pathotype P-0. The predicted amino acid sequence of CaPR-4 is very similar to those of other plant PR-4s, Southern blot ana lysis showed that small gene families of PR-4-related sequences were presen t in the pepper genome. Hot pepper cultivar Bugang, resistant to TMV-P-0 an d susceptible to TMV-P-1.2, induced CaPR-4 expression by pathotype P-0 inoc ulation in inoculated and systemic leaves, but not by pathotype P-1.2. Effe cts of exogenously applied abiotic elicitors upon the CaPR-4 expression wer e also examined. The expression of the CaPR-4 gene was stimulated by methyl jasmonate (MeJA), ethephon and wounding treatment. However, application of salicylic acid (SA) did not trigger the expression. Evidence is emerging t hat jasmonic acid and ethylene play key roles in the SA-independent pathway s of plant-pathogen interaction. Taken together, these results suggest that the CaPR-4 gene is one of the defense-related genes conferring resistance on pepper plants by the SA-independent pathway and the cross-talk between s ignaling compounds, jasmonic acid and ethylene could have a great regulator y potential in a plant's defense against TMV.