Identification and Sequence Analysis of Four S-RNase Genes in Plumcot (Prunus simonii Carr.)

Plumcot (Prunus simonii Carr.) is an interspecific hybrid between plum (P. salicina) and apricot (P. armeniaca) that plays an important role in non-timber forestry industry and making medicine. It exhibited S-RNase-based gametophytic self-incompatibility. In this study, four 5-RNase genes were identified and characterized. All of them displayed typical structural features of Prunus S-RNases, i.e. one signal peptide, five conserved regions, one Rosaceae-specific HV region and two introns. At the amino acid level, P. simonii S₁ shared an extremely high similarity (99.5%) with P. salicina Sh-RNase, indicating that they likely represented the same S-RNase. In comparison with other Prunus S-RNases, P. simonii S₁ showed a 65.6% to 80.4% similarity. Likewise, P. simonii S₂ and P. simonii S₄ were likely identical to P. armeniaca S₂-RNase and P. salicina Sb-RNase, respectively, and showed 66.5% to 78.7% similarity to other Prunus S-RNases. In the case of P. simonii S₃, it shared 66.5% to 89.6% similarity to other Prunus S-RNases. Similarity analysis well mirrors that plumcot originated from the cross of plum and apricot. Phylogenetic analysis indicated that the S-RNase divergence predated speciation in Prunus. Sequence information provided in the four plumcot SRNases will be useful for function analysis in self-incompatible response.