Three pathogen-inducible genes encoding lipid transfer protein from pepper are differentially activated by pathogens, abiotic, and environmental stresses.

The three cDNA clones, CALTPI, CALTPII, and CALTPIII, corresponding to pepper lipid transfer protein (LTP) genes were isolated from a pepper (Capsicum annuum) cDNA library from hypersensitive response (HR) lesions of leaves infected with Xanthomonas campestris pv. vesicatoria. The CALTP genes are well conserved in their coding region with 57-72% identity at the amino acid level, but display 72-83% identity at the nucleotide sequence level. The transcripts of the three CALTP genes differentially accumulated in pepper leaf, stem, and fruit tissues infected by X. campestris pv. vesicatoria, Phytophthora capsici and Colletotrichum gloeosporioides. The CALTP genes were also strongly induced in the systemic, upper leaves after immunization on lower leaves by either pathogenic or non-pathogenic bacteria. In situ hybridization results showed that the CALTPI mRNA was localized in phloem cells of vascular tissues in pepper leaf, stem and fruit tissues after pathogen infection. CALTPI and CALTPIII genes were predominantly expressed in various pepper tissues infected by pathogens, while infection by P. capsici and C. gloeosporioides did not induce the transcription of the CALTPII gene. Ethylene, methyl jasmonate and abscisic acid induced CALTPI and III gene expression in pepper leaves. Drought, high salinity, low temperature and wounding stresses also induced the expression of the CALTPI and CALTPIII genes in a similar manner. In contrast, only high salinity induced the CALTPII expression that was not generally affected by abiotic and other environmental stimuli. When compared with each other and with LTPs from other plants, CALTPI is more distantly related than CALTPII and CALTPIII sequences, indicating that the three pepper CALTP genes represent two different classes. These results thus show that CALTPI and CALTPIII genes, although different in sequence structure, are transcriptionally activated in pepper tissues by pathogen infection as well as abiotic and environmental stresses.