Identification of a short interspersed repetitive element in partially spliced transcripts of the bell pepper (Capsicum annuum) PAP gene: new evolutionary and regulatory aspects on plant tRNA-related SINEs.

In bell pepper, a gene encoding a major plastid-lipid associated protein is expressed as both partially and totally spliced transcripts (respectively PAP2 and PAP1). Although PAP is present as a single-copy gene in the bell pepper genome, Southern blots using PAP2 as a probe revealed multiple homologous copies. Analyses of the intronic sequence of PAP2 showed the existence of a 206bp short interspersed repetitive element (SINE) belonging to the Ts family of retrotransposons (Yoshioka et al., 1993). Comparison with PAP sequences in other Solanaceae species suggested that the structure of the gene is highly conserved: the two introns are inserted at the same position. However, the Ts insertion found in bell pepper is absent in tobacco and tomato. Studies using RT-PCR showed that in these latter species only totally spliced transcripts of PAP are present. On the other hand, RNA analyses of tobacco plants transformed with the bell pepper PAP revealed the presence of both totally and incompletely spliced transcripts. Altogether our results support the hypothesis that the Ts insertion into the first intron of PAP results in a splicing defect of the corresponding pre-mRNA. Based on the presence of peculiar, previously unidentified Ts elements, a possible horizontal transmission of Ts elements from animals to plants is discussed.