Articles
Isolation of European pear S-haplotypes using S-homozygotes derived from bud-selfing
Article number
1172_62
Pages
333 – 338
Language
English
Abstract
Gametophytic self-incompatibility is a mechanism that prevents self-fertilization through a specific pollen-pistil recognition, genetically controlled by the single S locus.
In the Pyrinae the S locus has a quite complex structure including a single female (pistil-expressed) gene, the S-RNase, and a number of male (pollen-expressed) F-box genes that act coordinately in a non-self-recognition system.
While each S-haplotype segregates as a single unit, gene duplication and genetic exchange seem to play an essential role in the evolution of pollen S-specificities; as a result, extant S-haplotypes differ for the number, position and arrangement of F-box genes.
So far, the genomic characterization of some S-haplotypes has been achieved using genomic libraries; the use of S-homozygotes can be an alternative source of information to characterize the pool of F-box genes belonging to a single haplotype.
To overcome the self-incompatibility barrier, selfing can be forced by manually pollinating pistils of immature flowers (bud-selfing): as the concentration of S-RNases in the early stages of the pistil development is not yet fully effective, a portion of self-pollen tubes can escape the inhibition.
The progeny obtained show a mendelian (1:2:1) segregation for the two parent S haplotypes, allowing the isolation of S-homozygotes in half the seedlings; since a low vigor is expected as a consequence of the increase in homozygosity, these genotypes are maintained and multiplied in vitro.
This material will be useful for the identification and characterization of F-box genes in different S-haplotypes, as a first step for investigating their roles in the determination of S specificities as well as their evolutionary dynamics.
In the Pyrinae the S locus has a quite complex structure including a single female (pistil-expressed) gene, the S-RNase, and a number of male (pollen-expressed) F-box genes that act coordinately in a non-self-recognition system.
While each S-haplotype segregates as a single unit, gene duplication and genetic exchange seem to play an essential role in the evolution of pollen S-specificities; as a result, extant S-haplotypes differ for the number, position and arrangement of F-box genes.
So far, the genomic characterization of some S-haplotypes has been achieved using genomic libraries; the use of S-homozygotes can be an alternative source of information to characterize the pool of F-box genes belonging to a single haplotype.
To overcome the self-incompatibility barrier, selfing can be forced by manually pollinating pistils of immature flowers (bud-selfing): as the concentration of S-RNases in the early stages of the pistil development is not yet fully effective, a portion of self-pollen tubes can escape the inhibition.
The progeny obtained show a mendelian (1:2:1) segregation for the two parent S haplotypes, allowing the isolation of S-homozygotes in half the seedlings; since a low vigor is expected as a consequence of the increase in homozygosity, these genotypes are maintained and multiplied in vitro.
This material will be useful for the identification and characterization of F-box genes in different S-haplotypes, as a first step for investigating their roles in the determination of S specificities as well as their evolutionary dynamics.
Authors
P. De Franceschi, P. Negri, F. Gennari, L. Dondini
Keywords
S-locus, S-RNase, Pyrinae, S-alleles evolution, S-genotyping
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