Regulation of a stylar transmitting tissue-specific gene in wild-type and transgenic tomato and tobacco.

We have characterized a gene, 9612, that is expressed predominantly in the styles of tomato pistils according to a tightly regulated temporal program. 9612 RNA levels were maximal in mature pistils from flowers at anthesis, with transcripts undetectable in pistils from flowers collected 5-7 days prior to anthesis. In situ localization of mRNA in tissue sections showed that expression of the gene is confined in the pistil to the outer five cell layers of the strands of transmitting tissue within the upper two-thirds of the style. The maximal levels of 9612 RNA detected in anthers and vegetative organs were more than 50-fold and 250-fold lower than the level in pistils, respectively. A homolog to the 9612 gene was detected in tobacco and was also found to be expressed predominantly in the style. The ability of the 5' flanking region of the tomato gene to appropriately regulate expression of a heterologous coding sequence was examined in transformed tomato and tobacco plants. In contrast to results with previously described regulated genes, the 9612 promoter functions correctly in the pistils of tomato plants, but fails to direct correct expression in tobacco plants. The sequence of the 9612 cDNA includes an open reading frame encoding a polypeptide of 404 amino acids with a highly hydrophobic amino-terminal region that may represent a signal peptide.