CHARACTERIZATION OF LENGTH POLYMORPHISMS AT THE 3'UTR OF THE MALOIDEAE S-RNASE AND ITS APPLICATION FOR S-GENOTYPING IN EUROPEAN PEAR

Length polymorphisms are especially suited for genotyping purposes since multiple allelic variants can be evaluated in a single PCR reaction. In fruit tree species of the Maloideae subfamily, the variation in length exhibited by the single intron of the S-RNase gene has been widely exploited for S-genotyping. However, introns of size 150±10 bp are very frequent, which often hamper the discrimination of many alleles by conventional agarose gel electrophoresis. In this study, full length cDNA sequences including the 5’ and 3’UTRs, corresponding to 18 S-RNases from three different species were analysed. The alignment of these sequences allowed characterizing a region at the 3’UTR highly variable in sequence and length, flanked upstream by the protein coding sequence and a short stretch of conserved nucleotide positions downstream. The convenience of this region for S-genotyping was evaluated by analysing length polymorphisms in European pear cultivars. Genomic PCR using a pair of consensus primers flanking the 3’UTR variable-region allowed to detect instances of S-Rnases, which were indistinguishable based on intron size but were polymorphic at this new region. Three new European pear S-RNase alleles could be characterized after this analysis.