Identification of the pepper SAR8.2 gene as a molecular marker for pathogen infection, abiotic elicitors and environmental stresses in Capsicum annuum

Pepper (Capsicum annuum L.) SAR8.2 genes, designated CASAR82A, B and C, which are induced by all the biotic and abiotic stresses, were isolated from a pepper cDNA library constructed with the mRNAs from pepper plants infected with Xanthomonas campestris pv. vesicatoria. The pepper CASAR82A, B and C gene products, which are very similar to each other in amino acid sequences, have 43-50% homology with those of tobacco SAR8.2 genes. The CASAR8.2 genes were not constitutively expressed in any of the organs of healthy pepper plants. In contrast, the CASAR82A gene was locally or systemically induced in pepper plants infected by X. campestris pv. vesicatoria, Colletotrichum coccodes or Phytophthora capsici. Strong induction of the CASAR82A gene also was found in pepper leaves treated with ethylene, methyl jasmonate, indole-3-acetic acid, abscisic acid, salicylic acid, benzothiadiazole, DL-beta-n-amino butyric acid or hydrogen peroxide. Interestingly, the transcription of the CASAR82A gene was rapidly triggered by high salinity, drought or low-temperature stresses, but not by mechanical wounding. In situ hybridization results revealed that the CASAR82A mRNAs were localized in phloem and epidermal cells of pepper leaf and stem tissues infected by C. coccodes and P. capsici, or treated with salicylic acid. These results thus suggest that pepper SAR8.2 genes may be valuable as a molecular marker for the detection of various pathogen infections, abiotic elicitors and environmental stresses.