Cloning and sequencing of cDNAs encoding two S proteins of a self-compatible cultivar of Petunia hybrida.

A defective S-allele, S(o), and a functional S-allele, Sx, have previously been found to be retained in an F1 hybrid of a self-compatible commercial cultivar of Petunia hybrida. Pistil proteins associated with these two alleles have also been identified. Their amino-terminal sequences have been found to share a high degree of similarity with those of S-proteins characterized from self-incompatible solanaceous species. Here we report the isolation and sequencing of cDNAs encoding S(o)- and Sx-proteins. Their deduced amino acid sequences contain all the consensus primary structural features of S-proteins from self-incompatible solanaceous species. Both proteins also have ribonuclease activity. The implications of these findings are discussed in relation to the presumed function of the S-protein in the self-incompatibility interaction.