A rat pancreatic ribonuclease fused to a late cotton pollen promoter severely reduces pollen viability in tobacco plants

The effects of an animal RNase fused to the late cotton pollen-specific pro moter G9 in a plant system were investigated. Expression of the chimeric ge nes G9-uidA and G9-RNase in tobacco plants showed that the 1.2-kb promoter fragment of the G9 gene was sufficient to maintain tissue and temporal spec ificity in a heterologous system. GUS (beta-glucuronidase) expression was d etected only in pollen from anther stage 6 through anthesis, with maximal G US activity in pollen from stage 10 anthers. Investigating the effects of t he rat RNase on pollen viability at stage 10, we found that pollen viabilit y was reduced from 79 to 8% and from 89 to 40%, in pollen germination and f luoresceine diacetate assays, respectively, in one G9-RNase transgenic line , suggesting a lethal effect of the RNase gene. This indicates that the rat RNase produces deleterious effects in this plant system and may be useful for engineering male sterility.