Two Novel Self-compatible S Haplotypes in Peach (Prunus persica)

Abstract

Peach (Prunus persica) as a species is self-compatible (SC), although most other Prunus fruit tree species are partially or fully self-incompatible. We previously identified 3 mutated S haplotypes, S1, S2, and S2m, that confer self-compatibility on commercial peach cultivars for fruit production. In this report, we identified 2 novel SC S haplotypes, S3 and S4, among 130 peach cultivars and strains consisting mainly of ornamental cultivars and wild strains. The S3 haplotype was found only in ornamental cultivars, while the S4 haplotype was found mainly in wild strains. S-RNases in the S3 and S4 haplotypes appeared to have no defects in their primary structures. S haplotype-specific F-box (SFB) sequences were also present in the S locus downstream of the S3- and S4-RNases. These SFB sequences were in a reverse transcriptional orientation as has been reported in most other functional Prunus S haplotypes; however, both SFB3 and SFB4 appeared to be mutated. DNA sequencing of the entire downstream region of SFB3, extending about 12 kbp to the stop codon of S-RNase, revealed the presence of a premature stop codon 975 bp downstream from the SFB3 start codon. No sequence homologous to SFB downstream of the stop codon was found. There was a 4946 bp insertion in the middle of SFB4. The original SFB4 sequence, obtained by removing the inserted sequence, encodes a typical SFB. Based on the 3 previously identified peach S haplotypes, we supposed that the S3 and S4 haplotypes were also SC pollen part mutant (PPM) S haplotypes. Here, we also discuss possible reasons for all peach S haplotypes identified so far having the PPM SC S haplotype