Identification of a Novel S-RNase Gene and S-Genotypes of Four Pear (Pyrus pyrifolia) Cultivars

Gametophytic self-incompatibility (GSI) is a genetically controlled mechanism to prevent inbreeding and promote out-crossing. Pyrus pyrifolia is a commercially important fruit tree that exhibits GSI. It is necessary to identify S-genotypes of cultivars for determination of cross-compatible combination prior to performing pear plantation and breeding programs. In this study, an important local cultivar 'Huobali' extensively used as parent in pear breeding programs, and its three progenies 'Mantianhong', 'Hongsucui' and 'Meirensu' were used for S-genotyping analysis by PCR-based molecular method. Agarose gel electrophoresis showed that two fragments were produced in each of the three progenies, while three in the 'Huobali'. After restriction digestion and sequencing analysis, the S-alleles in the four cultivars were determined. The allele of 345 bp from 'Huobali' was determined as a novel S-RNase allele that was tentatively denominated as S44-RNase. RT-PCR revealed that the S44-RNase was expressed specifically in the styles, which is consistent with the expression pattern of S-RNases. Comparison of genomic and cDNA sequences revealed an intron of 148 bp for the S44-RNase. At the amino acid level, it shared 65% to 93% similarity with other Maloideae S-RNases. This study will be helpful in pear production and breeding programs.