Temperature sensitive diphtheria toxin confers conditional male-sterility in Arabidopsis thaliana

A gene encoding a temperature-sensitive diphtheria toxin A chain (DTA) polypeptide was fused to the Arabidopsis thaliana tapetum-specific A9 promoter. Expression of the chimaeric gene in transgenic A. thaliana lines resulted in plants that were male-sterile, but female-fertile, when grown at 18 degrees C, and fully self fertile at 26 degrees C. No pollen grains were found on the anthers of transgenic plants grown at 18 degrees C, although aggregated pollen grains were found inside the anthers. Electron microscopy revealed discrete alterations in the tapetal cells of the male-sterile transgenic plants. The strength of the phenotype observed in segregants correlated with the level of expression of the gene and the copy number. The low frequency at which fully male-sterile plants were generated suggests that the temperature-sensitive DTA protein is disabled as a cytotoxin, relative to the wild-type protein activity.