Typing and distribution of the SFBB alleles encoded by four S-haplotypes of European pear (Pyrus communis L.)

Gametophytic self-incompatibility in pear (Pyrus species) is controlled by an S-locus haplotype, which encoded an S-RNase and multiple S-locus F-box brothers (SFBB) as female determinant and pollen determinants, respectively.
Self S-RNase is cytotoxic to self-pollen tube growth.
Whereas all non-self S-RNases are thought to be detoxified by multiple SFBBs collaboratively, which lead to pollen tube growth.
A complete suite of SFBB genes classifying into 22 types, is identified in the several S-haplotypes of Japanese pear, but not in European pear.
To identify a complete suite of SFBB genes of European pear in this study, we used CAPS marker system to perform S-genotyping for a chance seedling (S₂S₁₁₈) and an interspecific cultivar ‘Frontier’ (S₅S₁₀₁) between Japanese and European pear, which seedling and cultivar shared S₂– or S₅-haplotype of Japanese pear, respectively.
RNA-sequencing (RNA-seq) data on pollen of these interspecific pears was mapped to the reference sequences created from 24 types of SFBB sequences including S₂– or S₅–SFBB alleles.
The reads with sequence different from reference sequences were extracted to assemble S₁₁₈– or S₁₀₁–SFBB contig sequences.
Using these contig sequences as reference sequences, S₁₀₂– and S₁₀₅–SFBB contig sequences were assembled from RNA-seq data on pollen of ‘Bartlett’ (S₁₀₁S₁₀₂), ‘Aurora’ (S₁₀₁S₁₀₅) and ‘General Leclerc’ (S₁₀₂S₁₁₈) sharing S₁₀₁ or S₁₁₈-haplotype of European pear.
Among a total of 71 SFBB contig sequences of European pear obtained, 68 SFBB alleles were confirmed by RT-PCR cloning and sequencing, and were classified into 19 types (type 1-18 and 25). Many allelic pairs of the same type share higher degrees of amino acid sequence identity than those of S-RNase, suggesting that the same type SFBB recognize the same non-self S-RNases.
The absence of SFBB allele in several type might imply that S-haplotype must not have a conserved SFBB that recognizes its own S-RNase.

IV Asian Horticultural Congress – AHC2023

K. Tadokoro, M. Kobayashi, R. Fujimoto, T. Takasaki-Yasuda

Pyrus, European pear, Japanese pear, self-incompatibility, S-RNase, SFBB

https://doi.org/10.17660/ActaHortic.2024.1404.144