PD1, an S-like RNase gene from a self-incompatible cultivar of almond

Many flowering plants contain stylar S-RNases that are involved in self-incompatibility and S-like RNases of which the biological function is uncertain. This paper reports the deduced amino acid sequence of an S-like RNase gene (PD1) from the self-incompatible plant Prunus dulcis (almond). The amino acid sequence of PD1, which was derived from cDNA and genomic DNA clones, showed 34-86% identity to acidic plant S-like RNases reported so far, with the highest degree of similarity being to an S-like RNase from Japanese pear (Pyrus pyrifolia). Based on RNA hybridisation experiments it appears that, like for many other S-like RNases, the expression of PD1 is not pistil-specific. Analysis of the genomic structure revealed the presence of three introns, of which one is similar in location to that of the related S-RNase gene from Solanaceae and Rosaceae. At least four bands hybridising to PD1 were found upon Southern hybridisation, suggesting the presence of a multigene family of S-like RNase genes in almond. The putative biological function of PD1 is discussed.