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Title: Genetic Map-Based Location of the Red Clover (Trifolium pratense L.) Gametophytic Self-incompatibility Locus

item Riday, Heathcliffe
item KROHN, ANDREW - Northern Arizona University

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2010
Publication Date: 5/12/2010
Citation: Riday, H., Krohn, A. 2010. Genetic Map-Based Location of the Red Clover (Trifolium pratense L.) Gametophytic Self-incompatibility Locus. Theoretical and Applied Genetics. 121(4):761-767.

Interpretive Summary: Red clover, like many other plants, can not self pollinate. The genetic control for this trait is the gametophytic self incompatibility locus. The location of this locus is unknown. Using DNA molecular markers, we were able to identify the location of the locus on red clover linkage group one. Based on this research, we can now identify with reasonable accuracy individual self-incompatibility alleles at this locus using simple DNA tests. This knowledge will allow easy manipulation of self-incompatibility alleles in red clover breeding populations allowing: 1) 3/4 population hybrid red clover cultivar development (where 75% of a cross is hybrid compared to the normal 50% in a semi-hybrid population cross) and 2) more efficient paternity testing in red clover breeding populations leading to better red clover varieties. This research serves as a first step in identifying the DNA sequence of the self-incompatibility locus in red clover. This discovery also has possible implications for ecological and evolutionary research in clarifying the unique properties of clover self-incompatibility relative to other plant species.

Technical Abstract: Red clover is a hermaphadidic allogamous diploid (2n = 2x = 14) with a homomorphic gametophytic self-incompatibility (GSI) system red clover (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 was to use a mapping based approach to identify simple sequence repeats (SSR) that were closely linked to the GSI-locus. Previously published SSR were used in this effort (Sato et al., 2005). A bi-parental cross was initiated in which the parents were known to share one self-incompatibility allele (S-allele) in common. S-allele genotypes of 100 progeny were determined through test crosses and pollen compatibility. Pseudo F1 linkage analysis isolated the GSI-locus on red clover linkage-group one within 2.5cM 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 2.5cM and 4.7cM 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.