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.