title: Genetic map-based location of the red clover (Trifolium pratense L.) gametophytic self-incompatibility locus.
abstract: Red clover is a hermaphroditic allogamous diploid (2n = 2x = 14) with a homomorphic gametophytic self-incompatibility (GSI) system (Trifolium pratense L.). Red clover GSI has long been studied, and it is thought that the genetic control of GSI constitutes a single locus. Although GSI genes have been identified in other species, the genomic location of the red clover GSI-locus remains unknown. The objective of this study was to use a mapping-based approach to identify simple sequence repeats (SSR) that were closely linked to the GSI-locus. Previously published SSR markers were used in this effort (Sato et al. in DNA Res 12:301-364, 2005). A bi-parental cross was initiated in which the parents were known to have one self-incompatibility allele (S-allele) in common. S-allele genotypes of 100 progeny were determined through test crosses and pollen compatibility. Pseudo F(1) linkage analysis isolated the GSI-locus on red clover linkage-group one within 2.5 cM of markers RCS5615, RCS0810, and RCS3161. A second 256 progeny mapping testcross population of a heterozygous self-compatible mutant revealed that this specific self-compatible mutant mapped to the same location as the GSI-locus. Finally, 82 genotypes were identified whose parents putatively shared one S-allele in common from maternal halfsib families derived from two random mating populations in which paternal identity was determined using molecular markers. Unique S-allele identity in the two random mating populations was tentatively inferred based on haplotypes of two highly allelic linkage-group one SSR (RCS0810 and RCS4956), which were closely linked to each other and the GSI-locus. Paternally derived pollen haplotype linkage analysis of RCS0810 and RCS4956 SSR and the GSI-locus again revealed tight linkage at 2.5 and 4.7 cM between the GSI-locus and RCS0810 and RCS4956, respectively. The map-based location of the GSI-locus in red clover has many immediate applications to red clover plant breeding and could be useful in helping to sequence the GSI-locus.
authors.affiliation: US Dairy Forage Research Center, USDA-ARS, Madison, WI 53706, USA. heathcliffe.riday@ars.usda.gov
authors.forename: Heathcliffe
authors.initials: H
authors.lastname: Riday
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Krohn
mesh_terms: D002874:Chromosome Mapping / Q000379:methods*; D003433:Crosses, Genetic; D008040:Genetic Linkage; D056426:Genetic Loci / Q000235:genetics*; D055993:Germ Cells, Plant / Q000378:metabolism*; D015203:Reproducibility of Results; D029921:Trifolium / Q000235:genetics*
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