Self-compatible peach (Prunus persica) has mutant versions of the S haplotypes found in self-incompatible Prunus species

This study demonstrates that self-compatible (SC) peach has mutant versions of S haplotypes that are present in self-incompatible (SI) Prunus species. All three peach S haplotypes, S1, S2, and S2m, found in this study encode mutated pollen determinants, SFB, while only S2m has a mutation that affects the function of the pistil determinant S-RNase. A cysteine residue in the C5 domain of the S2m-RNase is substituted by a tyrosine residue, thereby reducing RNase stability. The peach SFB mutations are similar to the SFB mutations found in SC haplotypes of sweet cherry (P. avium) and Japanese apricot (P. mume). SFB1 of the S1 haplotype, a mutant version of almond (P. dulcis) Sk haplotype, encodes truncated SFB due to a 155 bp insertion. SFB2 of the S2 and S2m haplotypes, both of which are mutant versions of the Sa haplotype in Japanese plum (P. salicina), encodes a truncated SFB due to a 5 bp insertion. Thus, regardless of the functionality of the pistil determinant, all three peach S haplotypes are SC haplotypes. Our finding that peach has mutant versions of S haplotypes that function in almond and Japanese plum, which are phylogenetically close and remote species, respectively, to peach in the subfamily Prunoideae of the Roasaceae, provides insight into the SC/SI evolution in Prunus. We discuss the significance of SC pollen part mutation in peach with special reference to possible differences in the SI mechanisms between Prunus and Solanaceae.