Cloning and Characterization of a Self-compatible Sf Haplotype in Almond [Prunus dulcis (Mill.) D.A. Webb. syn. P. amygdalus Batsch] to Resolve Previous Confusion in Its Sf-RNase Sequence

Abstract

Most of the self-compatible (SC) cultivars of almond [ Prunus dulcis (Mill.) D.A. Webb. syn. P. amygdalus Batsch] have the S f haplotype. In this study, we cloned and characterized the S locus region of the S f haplotype of SC ‘Lauranne’. The relative transcriptional orientation of SFB f and S f -RNase and the physical distance between them are similar to those of other functional self-incompatible (SI) S haplotypes of Prunus , indicating that the genomic structure of the SC S f haplotype appears to be intact. Although there is no apparent mutation in the coding sequence of SFB f , the S f -RNase sequence in this study and previously reported S f -RNase sequences show discrepancies. First, as opposed to previous indications, the ‘Lauranne’ S f -RNase sequence encodes a histidine residue in place of a previously reported arginine residue in the conserved C2 region of Prunus S-RNase. Direct sequencing of the polymerase chain reaction products from the S f -RNase of ‘Tuono’ confirmed that ‘Tuono’ S f -RNase also encodes the histidine residue. We found another difference in the ‘Lauranne’ S f -RNase sequence and other reported S f -RNase sequences. Namely, ‘Lauranne’ S f -RNase encodes a phenylalanine residue in place of a previously reported leucine residue in the conserved C5 region of Prunus S-RNase. This is also the case for ‘Tuono’ S f -RNase . Expression analysis of S f -RNase and SFB f by reverse transcriptase–polymerase chain reaction showed that S f -RNase transcripts were barely detectable in pistil, whereas SFB f transcripts were accumulated at a similar level to the level that was observed with SFB of other functional SI S haplotypes of almond. We discuss the possible molecular mechanisms of SC observed with the S f haplotype with special references to the expression of S f -RNase .