Pollen ablation of transgenic tobacco plants by expression of the diphtheria toxin A-chain gene under the control of a putative pectin esterase promoter from Chinese cabbage.

We previously showed that a 383 bp (-274 to approximately +109) promoter of a pollen-specific gene, GBAN215-6, had a property of a late gene in pollen development in transgenic tobacco plants. It drove GUS gene expression from uninucleate microspores to pollen tube growth of trinucleated cells. To more precisely characterize the specificity of the promoter, we placed the diphtheria toxin A-chain (DTx-A) coding region under the control of the GBAN215-6 promoter. Transgenic tobacco plants containing the GBAN215-6/DTx-1 were phenotypically normal until an early stage of flowering. The dehisced anthers do not contain pollen grains and the filament length of stamen was shorter than that of normal plants. Microscopic examination showed that ablation of pollen by the expression of DTx-A was variable. The transgenic tobacco plants containing one copy of the DTx-A gene show 50% aborted and 50% normal pollen, which suggests that this gene acts gametophytically. However, most of the transgenic plants with high copy number were male-sterile. When these male-sterile tobacco plants were backcrossed as female with pollen from wild-type tobacco plants, the fruit capsule sizes and seed yields of the next generation (BC1 lines) were severely reduced and the segregation of male-sterile to fertile plants in BC1 seeds was not Mendelian.