The presence of a new S-RNase allele (S10) in Asian pear (Pyrus pyrifolia (Burm; Nakai))

A PCR (polymerase chain reaction) amplification method using newly designed S-RNase primers was carried out in five Korean-bred pear cultivars and ten Japanese-bred pear cultivars. A new S-RNase allele, designated as S-10, was discovered from 'Chengsilri', containing a 1513 bp and two exons (213 bp in total) that coded for a peptide of 71 amino acids. The S-10-RNase allele contained the three conserved cysteine residues peculiar to S-RNase in Japanese pear and one histidine residue essential for RNase activity. We compared nucleotide sequence similarity of the exon regions of ten pear S-RNase alleles. The nucleotide sequence of S-1 showed a high similarity to S-4 (97.4%) and the new S-10 shows 77.8% (S-5) to 84.4% (S-4) similarity with the other pear S-RNase alleles. S-10 had a unique restriction endonuclease site for 'HhaI', with digests yielding fragments of 1235 and 491 bp. The S-genotype of pear cultivar ('Chengsilri') was determined to be S5S10 by PCR-RFLP (restriction fragment length polymorphism). Cluster analysis of 49 known S-RNase alleles of the Rosaceae separated into two divergent groups are as follows: group I: pear and apple, group II: almond, sweet cherry and mume.