Characterization of a family of genes encoding a fruit-specific wound-stimulated protein of bell pepper (Capsicum annuum): identification of a new family of transposable elements.
A fruit-specific cDNA was used as a probe to isolate the two corresponding homologous genes (Sn-1 and Sn-2) of the bell pepper (Capsicum annuum) genome (nucleotide sequences were determined and have been submitted to the EMBL/GenBank/DDBJ databases under the accession numbers X79230 and X79231, respectively). Both genes have a single intron and numerous unusual long inverted repeat sequences. The introns share 87% homology and Sn-2 contains one 450 bp additional sequence with structural features of a transposable element, which is highly repetitive in the bell pepper genome. Surprisingly, analysis in data banks showed that genes encoding the potato starch phosphorylase (EC 126.96.36.199) and patatin contain a similar element, named Alien, in their 5′-upstream region. Alien elements are characterized by a conserved 28 bp terminal inverted repeat (TIR), small size, high AT content and the potential to form stable DNA secondary structures, and they have probably been inserted at TA target sites. Interestingly, the TIR of the Alien elements shares high homology with sequences existing in the TIR of extrachromosomal linear pSKL DNA plasmid of Saccharomyces kluyveri. Northern blot analyses detected Sn-1 transcripts principally in the red fruit, whereas no Sn-2 transcripts were detected in either of the samples monitored. Western blot analyses detected a 16.8 kDa Sn protein principally in the ripe red fruit and wounded areas of green unripe fruit. A comparison of the deduced amino acid sequence of Sn-1 with protein sequences in data banks revealed a significant homology with protein likely to be involved in the plant's disease resistance response. Analyses at the subcellular level showed that Sn-1 is localized in the membrane of vacuoles.