S-RNASE GENE OF NICOTIANA-ALATA IS EXPRESSED IN DEVELOPING POLLEN

In the solanaceous plant Nicotiana alata, self-incompatibility is cont rolled by a single, multiallelic locus (S locus) expressed in both pol len and pistil. Previously, we have shown cosegregation between allele s of the S locus and alleles of a gene that encodes a glycoprotein wit h ribonuclease activity (S-RNase). Furthermore, expression of the S-RN ase gene is apparently confined to the pistil and is correlated with t he onset of self-incompatibility. In this paper, we report that the S- RNase gene is also expressed at low levels in developing pollen. A tra nscript in developing pollen hybridized to a cDNA encoding the S-2-RNa se allele of the parent plant and did not hybridize to cDNAs encoding other S-RNase alleles. Two cDNAs for the S-2-RNase were cloned from a library derived from anthers of a plant homozygous for the S-2 allele and both corresponded to the coding sequence of the S-2-RNase. The pro duct of the S-RNase gene was detected by immunocytochemistry in the in tine of mature, hydrated pollen grains. These results are interpreted in the light of current knowledge of the structure of the S locus.