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In healthy, untreated pepper plants, transcripts of thionin (CATHION1) gene were induced in an organ-specific manner, as revealed by RNA blot analysis and in situ hybridization. The CATHION1 mRNAs were expressed in stems and flowers as well as roots, but not in leaves and fruits. In the stem and root tissues, the CATHION1 mRNA was present in endodermis and the phloem. In contrast, the transcripts were uniformly located in all the cells of flower tissues. Northern blot analysis and in situ hybridization were also performed to examine the temporal and spatial expression patterns of thionin (CATHION1) mRNA in leaf and fruit tissues of pepper (Capsicum annuum L.) infected by anthracnose pathogens Colletotrichum coccodes and C. gloeosporioides, respectively. Transcripts of the CATHION1 gene were more rapidly induced in pepper leaves at the 4- than at the 8-leaf stage by C. coccodes infection. Typical anthracnose symptoms were observed on green pepper fruits inoculated with C. gloeosporioides, but not on red pepper fruits. The transcript accumulation was more pronounced in green fruits than in red fruits upon C. gloeosporioides infection. The CATHION1 transcripts were detected in the phloem cells infected by anthracnose pathogens.

The pathogen- and ethylene-inducible pepper-basic pathogenesis-related (PR)-1 gene, CABPR1, was strongly expressed in pepper leaves by osmotic and oxidative stresses. The pepper CABPR1 was introduced into the Arabidopsis plants under the control of the cauliflower mosaic virus 35S promoter. Polymerase chain reaction-amplification with the Arabidopsis genomic DNA and Northern blot analyses confirmed that the pepper CABPR1 gene was integrated into the Arabidopsis genome, where it was overexpressed in the transgenic Arabidopsis plants under normal growth conditions. The constitutive overexpression of CABPR1 induced the expression of the Arabidopsis PR-genes including PR-4, PR-5 and PDF1.2. Enhanced resistance to phytopathogenic bacteria, Pseudomonas syringae pv. tomato DC3000, was also observed in the transgenic Arabidopsis plants. CABPR1 overexpression in the transgenic Arabidopsis caused enhanced seed germination under NaCI (ionic) and mannitol (non-ionic) osmotic stresses. Enhanced tolerances to high salinity and dehydration stresses during seed germination of the transgenic plants were not found at the early seedling stage. The transgenic Arabidopsis plants exhibited a higher tolerance to oxidative stress by methyl viologen at the seed germination, seedling and adult plant stages. These results suggest that the CABPR1 gene may function in the enhanced disease resistance and oxidative stress tolerance of transgenic Arabidopsis plants.

Northern blot and in situ hybridization analyses revealed that a pepper basic class II chitinase gene (CAChi2) is constitutively expressed in floral organs and root endodermis, but not in leaf, stem and fruit of pepper. Resistance of pepper leaves to Colletotrichum coccodes infection at a late growth stage was correlated with induction of beta-1,3-glucanase and PR-1 mRNA, but not of chitinase (CAChi2) mRNA. Transcriptional activation of the CAChi2 gene in pepper leaves occurred during anthracnose development. The CAChi2 transcripts were mainly localized in phloem cells of vascular tissues of pepper leaves infected with C. coccodes. The CAChi2 gene was also differentially induced in leaf and stem tissue by treatment with abscisic acid (ABA), sodium chloride or drought. Strong accumulation of the CAChi2 transcripts occurred in pepper stem tissues due to high salt and drought, and also due to treatment with ABA. These results suggest involvement of the chitinase gene in protection of pepper plants against the pathogen, but also document cross talk with stress signals mediated by ABA, high salinity and drought.

A new basic pathogenesis-related (PR)-1 cDNA (CABPR1) was isolated from a cDNA library of pepper leaves infected with Xanthomonas campestris pv. vesicatoria. The full-length clone contains an open reading frame of 531 nucleotides encoding 177 amino acid residues with a predicted molecular mass of 20241 and pI of 8.1. The deduced amino acid sequence of CABPR1 has a high level of identity with PR-1 proteins from tobacco and tomato. Expression of the CABPR1 mRNA was greatly induced in an incompatible interaction of pepper leaves with X. campestris pv. vesicatoria. Accumulation of the basic PR-1 mRNA in the bacteria-infected leaves was intrinsically associated with the induction of ethylene biosynthesis. Treatment with 1-aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, strongly suppressed the induction of PR-1 mRNA expression in the bacteria-infected leaves. These data suggest that ethylene may function as a strong signal elicitor in the activation of PR-1 genes, eventually mediating the plant defence response. Phytophthora capsici infection also distinctly stimulated ethylene biosynthesis, together with accumulation of PR-1 mRNA. Expression of the basic PR-1 mRNA was also induced in the pepper leaves by treatment with dl-β-amino-n-butyric acid or salicylic acid, but not by wounding. Treatment with methyl jasmonate, in combination with salicylic acid, strongly induced the PR-1 transcripts. The basic PR-1 gene expression occurred in untreated roots, flowers and green fruit of pepper but not in leaf, stem or red fruit.

A stellacyanin cDNA clone (CASLP1) was isolated from a pepper cDNA library from hypersensitive response (HR) lesions of leaves infected with an avirulent strain of Xanthomonas campestris pv. vesicatoria. The deduced amino acid sequences of CASLP1 are homologous to those of stellacyanins from cucumber, maize, pea and Arabidopsis. The CASLP1 mRNA was not constitutively expressed in all organs of pepper, but strongly induced and accumulated in pepper tissues infected with X. campestris pv. vesicatoria, Colletotrichum coccodes, Phytophthora capsici or C. gloeosporioides. In situ hybridization results revealed that CASLP1 transcripts were strongly localized in the phloem areas of vascular bundles in infected tissues of pepper stems and fruits. CASLP1 mRNA accumulation was found in lower pepper leaves infected by either virulent or avirulent strains of X. campestris pv. vesicatoria and non-pathogenic Pseudomonas fluorescens, but not in uninoculated upper leaves. Induction of this CASLP1 gene occurred in pepper leaves applied with methyl jasmonate (MeJA), but not with ethylene, salicylic acid, dl-beta-amino-n-butyric acid and benzothiadiazole. Accumulation of CASLP1 transcripts was locally or systemically induced in pepper leaves upon mechanical wounding and was activated in a MeJA-dependent manner. The CASLP1 transcript was also strongly induced in leaf and stem tissues after exposure of pepper plants to abscisic acid, salt and drought.