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 Shaplotypes, S[1], S[2], and S[2m], that confer self-compatibility on commercial peach cultivars for fruit production. In this report, we identified 2 novel SC S haplotypes, S[3] and S[4], among 130 peach cultivars and strains consisting mainly of ornamental cultivars and wild strains. The S[3]haplotype was found only in ornamental cultivars, while the S[4] haplotype was found mainly in wild strains. S-RNases in the S[3] and S[4] haplotypes appeared to have no defects in their primary structures. S haplotype-specific F-box (SFB) sequences were also present in the Slocus downstream of the S[3]- and S[4]-RNases. These SFB sequences were in a reverse transcriptional orientation as has been reported in most other functional Prunus S haplotypes; however, both SFB[3] and SFB[4] appeared to be mutated. DNA sequencing of the entire downstream region of SFB[3], extending about 12 kbp to the stop codon of S-RNase, revealed the presence of a premature stop codon 975 bp downstream from the SFB[3] start codon. No sequence homologous to SFB downstream of the stop codon was found. There was a 4946 bp insertion in the middle of SFB[4]. The original SFB[4] sequence, obtained by removing the inserted sequence, encodes a typical SFB. Based on the 3 previously identified peach Shaplotypes, we supposed that the S[3] and S[4] 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.

サクラ属果樹の多くが自家不和合性を示すが, モモは特異的に種全体が自家和合性を示す. 我々はこれまでの研究で, 果実生産用モモの主要栽培品種から 3 種の変異型自家和合性 S ハプロタイプを同定した. 本研究では野生種および観賞用品種を中心に 130 品種・系統を調査し, 新たに 2 つの S ハプロタイプを発見し, S3 および S4 ハプロタイプと命名した. S3 ハプロタイプは観賞用品種にのみ分布し, S4 ハプロタイプは主に野生種を中心に分布することが明らかとなった. これらの S ハプロタイプはいずれも雌ずい S 遺伝子である S-RNase の塩基配列に欠失や挿入は確認できず, 雌ずい側の機能は正常であると推察された. 一方, 花粉 S 遺伝子である SFB にはいずれも変異が存在し, 不完全な SFB がコードされていた. SFB3 はスタートコドンから 975 bp 下流にストップコドンが存在していた. SFB4 は 4946 bp の挿入配列が見いだされ, 挿入配列の内部にストップコドンが存在した. 従って新規に同定された 2 種類の S ハプロタイプは, これまで報告したモモの 3 種類の S ハプロタイプと同様に花粉側の機能を失った自家和合性 S ハプロタイプであると推察された. モモで同定された全ての S ハプロタイプが, 花粉 S 遺伝子に変異の生じた自家和合性 S ハプロタイプであることの理由を考察した.