XVI International Botanical Congess

Self-incompatible (SI) plants can recognize and reject self" pollen. Often, SI species also reject pollen from related self-compatible (SC) species in a type of inter-specific incompatibility known as unilateral incompatibility (UI). S-RNases are involved in both systems, however pollen rejection in UI is less specific than in SI. To understand this difference in specificity, we determined the effect of three particular transgenically expressed RNases on pollination phenotypes. The first is a non-S-RNase, from E. coli. The Second is a chimeric S-RNase gene that is defective for pollen rejection in SI. The third is an exceptional S-RNase that appears to be defective for UI-mediated rejection of N. plumbaginifolia. The genes for these RNASES were expressed to high levels in the appropriate Nicotiana background, and the pollination phenotypes of these plants determined.