Identification and evolutionary characterization of SFBB genes in ‘Yali’ and its spontaneous self-compatible mutant ‘Jinzhui’ (Pyrus bretschneideri)

Abstract

Pears carry a gametophytic self-incompatibility (SI) system. In this system, S-RNase is the SI pistil determinant, and S-locus F-box brothers (SFBBs) are candidate pollen determinants. However, compared with apple, fewer SFBB genes were identified from pear, possibly caused by the lack of economic and effective methods. Here, we used transcriptome sequencing on ‘Yali’ (Pyrus bretschneideri) to obtain sequence fragments of SFBB genes and then used polymerase chain reaction (PCR) to amplify the whole sequence of SFBB genes. Twenty-seven SFBB genes, including 22 full-length and five nonfull-length SFBB genes, were identified in ‘Yali’ (P. bretschneideri). SFBBs linkage analysis by PCR-enzyme-linked immunoassay (ELISA) showed that 12 SFBB genes belong to the S21 locus, and 15 SFBB genes belong to the S34 locus. Phylogenetic analysis showed that SFBB genes from Pyrus were divided into 26 types, more than the original eight types. The intrahaplotypic divergence of SFBBs is high and comparable to the allelic diversity of S-RNase, which is consistent with a nonself-recognition SI system. In addition, the expression level of PbrSFBBs in ‘Jinzhui’, the only known haploid pollen of a self-compatible mutant, was mostly approximately two times higher than in ‘Yali’, which may be the reason for the self-compatible mutant.

Keywords

• Pyrus bretschneideri
• Self-incompatibility
• F-box protein
• Genotyping
• Transcriptome sequencing