Molecular characterization of newS-RNases (‘S31’ and ‘S32’) in apple (Malus ×domestica Borkh.)’) in apple (Malus ×domestica Borkh.)

Apple exhibits gametophytic self-incompatibility (GSI) that is controlled by the multiallelic S-locus. This S-locus encodes polymorphicS ribonuclease (S-RNase) for the pistil-part 5 determinant. Information aboutS-genotypes is important when selecting pollen donors for fruit production and breeding of new cultivars. We determined the 5-genotypes of ‘Charden’ (S2S3S4), ‘Winesap’ (S1S28), ‘York Imperial’ (S2S31), ‘Stark Earliblaze’ (S1S28), and ‘Burgundy’ (S20S32), byS-RNase sequencing and S-allele-specific PCR analysis. Two newS-RNases, S31 and S32, were also identified from ‘York Imperial’ and ‘Burgundy’, respectively. These newS-alleles contained the conserved eight cysteine residues and two histidine residues essential for RNase activity. Whereas S31 showed high similarity to S20 (94%), S32 exhibited 58% (to S24) to 76% (to S25) similarity in the exon regions. We designed newS-allele-specific primers for amplifying S31- and S32-RNasc-specific fragments; these can serve as specific gene markers. We also rearranged the apple S-allele numbers containing those newS-RNases. They should be useful, along with anS-RNase-based PCR system, in determining S-genotypes and analyzing new alleles from apple cultivars.