THE EXPRESSION OF A POTATO (SOLANUM-TUBEROSUM) S-RNASE GENE IN NICOTIANA-TABACUM POLLEN

Self-incompatibility in the Solanaceae is controlled by a single multi allelic genetic locus, the S locus. The stylar gene products of the S locus are abundant glycoproteins with ribonuclease activity, secreted in the transmitting tract tissue of the pistil. To investigate the str uctural and functional integrity and possible phenotypic effects of ex pression of the S-gene product in the male gametophyte, N. tabacum pla nts were transformed with a construct containing the genomic S-2-RNase coding sequence from S. tuberosum under the control of the promoter o f the pollen-specific LAT52 gene from tomato. The expression pattern o f the S-2 RNase in the male gametophyte at both the protein and RNA le vel was found to be identical to that already reported for expression of the beta-glucuronidase (GUS) gene directed by the LAT52 promoter in transgenic tomato and tobacco. The S-2-RNase gene fusion led to a tis sue-specific and developmentally regulated accumulation of the S-2 pol ypeptide in pollen of transgenic tobacco plants. The transgenic protei n product was of the same size and charge as the potato stylar product , had ribonuclease activity, and was glycosylated. The transgenic plan ts, however, did not show any morphological variations in their flower organs, and their fertility was not influenced by the accumulation of the S-2-RNase protein in pollen.