Genetic and Functional Analysis of S-alleles in Chinese Pear and the self-compatible mutant ‘Zaoguan’

Self-incompatibility is a widespread and effective genetic mechanism in flowering plants that promotes outcrossing and prevents inbreeding. Chinese pear ( Pyrus species) exhibits typical gametophytic self-incompatibility (GSI), which often results in low fruit set and yield instability in orchards due to self-pollination. In this study, we characterized the S -genotypes of 24 pear accessions and identified 25 previously reported and 1 novel S 69 -RNase allele. We also cloned the full-length sequences of 10 S -alleles, including the novel S 69 -RNase , using 5'/3'-rapid amplification of cDNA ends (RACE) and homologous cloning and submitted the sequences to GenBank. The novel S 69 -RNase allele was exclusively expressed in the style and showed high amino acid sequence similarity to Malus S 8 -RNase (97.81%), suggesting that S-RNase s existed before the speciation between Pyrus and Malus . Among the 10 S -alleles, S 41 , S 48 , S 53 , S 59 , S 64 , and S 65 RNases from Chinese pear accessions exhibited high sequence identity with those from European pear, indicating that oriental and occidental pear may share the same allele pool at the S -locus. Using orchard-based reciprocal cross experiments, we analyzed the recognition specificity between S 59 -RNase from Chinese pear and S 108 -RNase from European pear and found that they function as the same S -haplotype. Further, we investigated the genotypes and self-incompatibility/compatibility of ‘Zaoguan’ hybrid progeny and revealed that the self-compatible mutation in ‘Zaoguan’ was not closely linked to the S 17 -RNase locus, providing new insights into the genetic mechanisms underlying self-compatibility in pear. These findings offer valuable insights for pear production and breeding and contribute to a new understanding of the self-incompatibility mechanism.