A RETROTRANSPOSON-LIKE SEQUENCE LINKED TO THE S-LOCUS OF NICOTIANA-ALATA IS EXPRESSED IN STYLES IN RESPONSE TO TOUCH

We have identified a family of repetitive sequences in the genome of N icotiana alata named Tna1 (Transposon of N. alata). The first element we characterised was on a genomic clone for the N. alata S-6-ribonucle ase (S-6-RNase), a gene required for self-incompatibility in this spec ies. The DNA sequence of this element resembles the integrase domain o f retrotransposons of the gypsy class and is most similar to a retrotr ansposon from Lilium henryi. A transcript present in N. alata styles ( self-incompatibility genotype S6S6) hybridized to Tna1 and accumulated in the style following either pollination or touching. This transcrip t was cloned from a cDNA Library and was encoded by a second, partial Tna1 element. Neither the transcribed sequence nor the original Tna1 e lement contain an open reading frame or is likely to be able to transp ose. The second element was mapped using a population of N. alata plan ts segregating for alleles of the self-incompatibility locus and is cl osely linked to the S-6-allele. The Tna1 element is present in a numbe r of Nicotiana species and appears to have been active at least twice during the evolution of this genus.