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The use of genetic cell ablation through the expres- sion of rnases, toxic genes or antisense mrna along with promoters directing the expression to different cell types has aided in the molecular dissection of plant develop- mental processes. the cell ablation techniques have been used to study male gametogenesis, by visualization of the developmental events in the absence of specific cells, and can be used as a tool to produce male sterility (mariani et al., 1990; mccormick, 1991; nasrallah et al., 1991; denis 1993; goldberg et al ., 1993; roberts 1995; twell, 1995; zhan ., 1996; beals and goldberg, 1997). male gametogenesis occurs in the sporophytic tissue of the anther and begins with the meiotic division of a diploid sporogenic cell (pollen mother cell) into a tetrad of haploid microspores, which later undergo an asymmetric mitotic di- vision, resulting in pollen grains. these pollen grains contain a small generative cell within a larger vegetative cell. the pollen grains mature and undergo another mitotic division, before or after germination, giving rise to two sperm cells that complete the process with the double fertilization of the egg and the central cell (bedinger, 1992; mccormick, 1993). the genes expressed during male gametogenesis have been classified as “early” genes, which become active soon after meiosis is complete, or as “late” genes, when become active after microspore mitosis (mascarenhas, 1990). about 75% of the mrnas present in mature pollen of trades- cantia occur in two or more abundant classes, compared to only 35% of mrnas in shoots (mascarenhas, 1988). this, and the fact that the late pollen-specific cotton gene g9 was isolated by differential screening (john and petersen, 1994), make it probable that is a high-abundance tran- script (scott 1991). thus, the 5’ flanking region of the g9 gene can promote pollen-specific expression, cer- tainly at levels high enough for cell ablation. the native gene shows maximal expression on the day of anthesis (john and petersen, 1994), when there is an existing stored pool of presynthesized rnas (mrna, rrna and trna) that will be used for protein translation during pollen germination (mascarenhas, 1988; clarke and newbigin, 1993). it indi- cates that is an adequate promoter to monitor the effi- cacy of an rnase gene. if the rnase gene works properly in the plant system, it may cause a reduction in pollen ger- mination by depletion of protein synthesis. the rnases used to investigate the role of specific anther genes/tissues and to induce male sterility have fun- gal or bacterial origin (mariani 1990; denis et al., 1993; roberts 1995; zhan ., 1996; beals and goldberg, 1997), and were reported to present thermo- instability (denis 1993). we investigated the effects on male gametogenesis and pollen viability, of an animal rnase fused to the cotton pollen promoter, and the possibility of using this system to generate male sterility

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