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 putative 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 P0. The predicted amino acid sequence of CaPR-4 is very similar to those of other plant PR-4s. Southern blot analysis showed that small gene families of PR-4-related sequences were present in the pepper genome. Hot pepper cultivar Bugang, resistant to TMV-P0 and susceptible to TMV-P1.2, induced CaPR-4 expression by pathotype P0 inoculation in inoculated and systemic leaves, but not by pathotype P1.2. Effects of exogenously applied abiotic elicitors upon the CaPR-4 expression were 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 that jasmonic acid and ethylene play key roles in the SA-independent pathways 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 signaling compounds, jasmonic acid and ethylene could have a great regulatory potential in a plant's defense against TMV.     

Molecular cloning and expression of the hot pepper ERabp1 gene encoding auxin-binding protein

The 22 kDa auxin-binding proteins in higher plants have received considerable attention as candidates for an auxin receptor. A cDNA clone Ca-ERabp1 of hot pepper (Capsicum annum) was isolated using the oligonucleotides as PCR primers. The cDNA codes for a polypeptide related to the major 22 kDa auxin-binding protein from maize and Arabidopsis ERabp1. The deduced amino acid sequence contains an endoplasmic reticulum retention signal, the KDEL sequence located at the C-terminal end, and has two possible auxin-binding sites, HRHSCE and YDDWSVPHTA conserved sequences. Northern hybridization analysis revealed that the Ca-ERabp1 gene is differentially expressed in total RNA isolated from different organs of a pepper plant, showing the highest level of expression in fruits but barely detectable in leaves and roots.