Direct genotyping of single pollen grains of a self-compatible mutant of Japanese pear (Pyrus pyrifolia) revealed inheritance of a duplicated chromosomal segment containing a second S-haplotype

Nobuko Mase,Norio Takada,Toshihiro Saito,Yutaka Sawamura,Toshiya Yamamoto,Hiroyuki Iketani,Sogo Nishio

doi:10.1007/s10681-014-1168-3

Abstract

AbstractRadiation mutant 415-1, which is the first known diploid pollen-part self-compatible mutant of pears (Pyrus spp.), has a decreased ability to produce pollen. To determine whether the self-compatibility trait is associated with this defect, we directly analyzed the genotypes of individual pollen grains by using polymerase chain reaction amplification of DNA from single pollen grains. We isolated single pollen grains from 415-1 and succeeded in genotyping the S-RNase gene and three simple sequence repeat (SSR) markers in linkage group 17. Out of 173 individual pollen grains, 28 (16 %) were S-heteroallelic. These pollen grains had two alleles each of the S-RNase gene and of two linked SSR loci, all on a duplicated chromosomal segment, but only one allele of a non-duplicated locus farther away on the same chromosome. The segregation ratio of each marker in the pollen from 415-1 was approximately the same as that observed in outcross progeny. This suggests that the decrease in frequency of pollen with the duplicated S-haplotype occurred during meiosis or pollen formation, but that the probability of fertilization by S-heteroallelic pollen is equal to that of single-allelic pollen. However, the partial sterility in 415-1 can also be attributed to one or more unidentified lethal mutations unlinked to the duplicated segment encompassing the S-haplotype. Single-pollen genotyping can be used in a variety of applications in genetic research because in cases where all pollen genotypes are proportionately represented in the progeny, segregation ratios can be obtained without producing the next generation.

Highlights

Self-incompatibility in flowering plants is a genetic system that prevents inbreeding and promotes genetic diversity
We compared the occurrence of the duplicated S-haplotype in pollen and progeny and we examined the possible involvement of the duplicated haplotype in the pollen morphology and pollen-producing capability of 415-1
Using single-pollen genotyping, we succeeded in a straightforward proof of the presence of S-haplotype duplication in pollen grains of 415-1 that did not require analysis of progenies

Summary

Introduction

Self-incompatibility in flowering plants is a genetic system that prevents inbreeding and promotes genetic diversity (de Nettancourt 2001). SLF (S-locus F-box) (Entani et al 2003) or SFB (S haplotype-specific F-box protein) (Ushijima et al 2003) that is predicted to recognize self S-RNase, whereas in the Pyrinae, there are multiple F-box proteins called SFBB (S locus F-box brothers) (Sassa et al 2007; Minamikawa et al 2010) that are predicted to collaborate in recognizing non-self S-RNase (Kakui et al 2011; Saito et al 2012) In either case, these plants require cross pollination with other cultivars to set fruit. The only known self-compatible mutant useful for breeding purposes was identified in ‘Osa-Nijisseiki’, a bud sport of ‘Nijisseiki’ It exhibits style-specific inactivation of the S4-allele, it is a stylar-part self-compatible mutant (SPM) (Sassa et al 1997). It is likely that inbreeding depression will occur in the progeny of crosses between cultivars originating from ‘Osa-Nijisseiki’ or ‘Nijisseiki’ in the future (Sato et al 2008)

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Conclusion