Full Length cDNA Sequence of Pear (Pyrus bretschneideri Rehd.) S29-RNase and S29-Allele Identification

Chinese white pear (Pyrus bretschneideri Rehd.) belongs to Rosaceae that exhibits characteristic gametophytic self-incompatibility. This type of self-incompatibility is controlled by S-locus which carries a series of multi-allelic alleles encoding S-RNases. To elucidate the function of S-allele and the possible molecular mechanism of gametophytic self-incompatibility in Chinese white pear, full length cDNA encoding S₂₉-RNase was cloned by rapid amplification of cDNA ends (RACE) approach from cultivars ‘Mili’ (S₁₉S₂₉) and ‘Zaomi’ (S₁₉S₂₉). The S₂₉-RNase gene contained an open reading frame of 684 nucleotides encoding 228 amino acid residues. S₂₉-RNase displayed typical sequence features of rosaceous S-RNases, i.e. five conserved regions (C1, C2, C3, RC4 and C5) and a hypervariable (HV) region. At the deduced amino acid level, S₂₉-RNase showed 30% to 92% similarities with other rosaceous S-RNases. Phylogenetic analysis revealed that rosaceous S-RNases occurred before divergence of species, but after divergence of subfamilies Maloideae and Amygdaloideae. Genomic PCR amplification with primer combination FTQQYQ and anti-(I/T)IWPNV followed by digestion with the restriction enzyme AccII allowed effectively distinguishing S₂₉-allele from other pear S-alleles.