AN INVESTIGATION OF THE ROLE OF THE ANTHER TAPETUM DURING MICROSPORE DEVELOPMENT USING GENETIC CELL ABLATION

The effects on anther development of a fusion of the Arabidopsis anthe r-specific apg gene promoter to a ribonuclease (barnase) in transgenic tobacco plants were examined. Contrary to expectations, viable pollen grains were produced by these plants despite the demonstration that r ibonuclease expression in the microspores and tapetum caused targeted cell ablation. Transformed plants were reduced in male fertility due t o ablation of a proportion of pollen dependent on apg-barnase locus nu mber. Plants were otherwise phenotypically normal and fully female fer tile, confirming the anther-specific nature of the apg promoter. In mi crospores inheriting an apg-barnase locus following meiosis, loss of c ell viability, as judged by fluorescein diacetate staining, occurred d uring mid to late microspore development. Microspores not inheriting a transgene went on to mature into viable pollen grains. Premature dege neration of the tapetum was also observed as a result of apg-barnase e xpression, but this did not appear to disrupt the subsequent microspor e and pollen developmental programmes. This was substantiated by obser vations of microspore development in plants in which the tapetum was r escued from ablation by crossing in a second transgene encoding a tape tum-specific inhibitor of the ribonuclease. It was determined that tap etum cell disruption occurs at the early to mid uninucleate microspore stage in apg-barnase transformants. The data presented show that afte r this point in microspore development the tapetum is no longer essent ial for the production of viable pollen in tobacco.