A segmental duplication encompassing S-haplotype triggers pollen-part self-compatibility in Japanese pear (Pyrus pyrifolia)

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

doi:10.1007/s11032-013-9938-5

Abstract

Self-compatible mutants of self-incompatible crops have been extensively studied for research and agricultural purposes. Until now, the only known pollen-part self-compatible mutants in Rosaceae subtribe Pyrinae, which contains many important fruit trees, were polyploid. This study revealed that the pollen-part self-compatibility of breeding selection 415-1, a recently discovered mutant of Japanese pear (Pyrus pyrifolia) derived from γ-irradiated pollen, is caused by a duplication of an S-haplotype. In the progeny of 415-1, some plants had three S-haplotypes, two of which were from the pollen parent. Thus, 415-1 was able to produce pollen with two S-haplotypes, even though it was found to be diploid: the relative nuclear DNA content measured by flow cytometry showed no significant difference from that of a diploid cultivar. Inheritance patterns of simple sequence repeat (SSR) alleles in the same linkage group as the S-locus (LG 17) showed that some SSRs closely linked to S-haplotypes were duplicated in progeny containing the duplicated S-haplotype. These results indicate that the pollen-part self-compatibility of 415-1 is not caused by a mutation of pollen S factors in either one of the S-haplotypes, but by a segmental duplication encompassing the S-haplotype. Consequently, 415-1 can produce S-heteroallelic pollen grains that are capable of breaking down self-incompatibility (SI) by competitive interaction between the two different S factors in the pollen grain. 415-1 is the first diploid pollen-part self-compatible mutant with a duplicated S-haplotype to be discovered in the Pyrinae. The fact that 415-1 is not polyploid makes it particularly valuable for further studies of SI mechanisms.

Highlights

Self-incompatibility (SI) is a reproductive strategy to prevent inbreeding and maintain genetic diversity in flowering plants
This study revealed that the pollen-part self-compatibility of breeding selection 415-1, a recently discovered mutant of Japanese pear (Pyrus pyrifolia) derived from c-irradiated pollen, is caused by a duplication of an S-haplotype
Iketani Graduate School of Life and Environmental Science, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8572, Japan. These results indicate that the pollen-part self-compatibility of 415-1 is not caused by a mutation of pollen S factors in either one of the S-haplotypes, but by a segmental duplication encompassing the S-haplotype

Summary

Introduction

Self-incompatibility (SI) is a reproductive strategy to prevent inbreeding and maintain genetic diversity in flowering plants (de Nettancourt 2001). The families Solanaceae, Rosaceae, and Plantaginaceae exhibit SRNase-based SI that is gametophytically controlled by a multigene complex, the S-locus. The genes at this locus encode S-RNase (McClure et al 1989; Sassa et al 1996; Xue et al 1996) as a stylar factor and F-box proteins called S-locus F-box (SLF) in an Antirrhinum interspecific hybrid (Lai et al 2002), Prunus mume Siebold &. Webb (Ushijima et al 2003) as pollen factors for self/non-self recognition These two genes at the S-locus segregate as a single unit referred to as the S-haplotype. When a pollen S-allele matches either one of the S-alleles of the pistil, S-RNase secreted by the pistil tissue degrades the ribosomal RNA in the pollen tube produced by that pollen grain, resulting in the inhibition of pollen tube elongation and the prevention of fertilization

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