ANTISENSE SUPPRESSION OF S-RNASE EXPRESSION IN NICOTIANA USING RNA-POLYMERASE-II-TRANSCRIBED AND RNA-POLYMERASE-III-TRANSCRIBED GENE CONSTRUCTS

In the Solanaceae, self-incompatibility is controlled by a single, multi-allelic ('S') locus. One product of this locus is a ribonuclease, the S-RNase, which is expressed predominantly in mature pistils and has recently been shown to cause allele-specific pollen rejection in transgenic plants. Hybrid Nicotiana phumbaginifolia x N. alata plants were used to test the effects of antisense suppression of the S-A2-RNase from N. alata using three different gene constructs: two driven by RNA polymerase II-transcribed promoters, and the third, containing a truncated soybean tRNA(met-i) gene, transcribed by RNA polymerase III. All three constructs caused suppression of S-RNase activity in the transgenic plants. Unexpectedly, the CaMV 35S promoter was more effective for antisense suppression than the tissue specific tomato ChiP promoter. Antisense suppression of S-RNase correlated with low sense S-A2 transcript levels and high antisense S-A2 transcript levels. Untransformed hybrids that contained the N. alata S-A2 allele were incompatible with N. alata S-A2 pollen, while transgenic plants with suppressed S-A2 gene expression accepted the pollen. The utility of this hybrid plant system for studying some aspects of antisense gene suppression is discussed.