Comparing the Linkage Maps of the Close Relatives Arabidopsis lyrata and A. thaliana

Abstract

We have constructed a genetic map of Arabidopsis lyrata, a self-incompatible relative of the plant model species A. thaliana. A. lyrata is a diploid (n ϭ 8) species that diverged from A. thaliana (n ϭ 5) ‫5ف‬ MYA. Mapping was conducted in a full-sib progeny of two unrelated F 1 hybrids between two European populations of A. lyrata ssp. petraea. We used the least-squares method of the Joinmap program for map construction. The gross chromosomal differences between the two species were most parsimoniously explained with three fusions, two reciprocal translocations, and one inversion. The total map length was 515 cM, and the distances were 12% larger than those between corresponding markers in the linkage map of A. thaliana. The 72 markers, consisting of microsatellites and gene-based markers, were spaced on average every 8 cM. Transmission ratio distortion was extensive, and most distortions were specific to each reciprocal cross, suggesting cytoplasmic interactions. We estimate locations and most probable genotype frequencies of transmission ratio distorting loci (TRDL) with a Bayesian method and discuss the possible reasons for the observed distortions.A RABIDOPSIS thaliana has become the plant molec-B. nigra and A. thaliana, the conserved segments were ular biology model organism partly because of its only ‫8ف‬ cM in length (Lagercrantz 1998). As the diververy small genome size. It has also become a focus of gence time between Brassica and A. thaliana is estimated plant comparative genomics studies (Schmidt 2002).to be ‫02ف‬ MY, this gives rise to a high rate of chromoSince the sequencing of the A. thaliana genome (Arabisomal evolution. The rapid rate of chromosomal evoludopsis Genome Initiative 2000), the genomic organition was assigned to the polyploid Brassica lineage. A zation of A. thaliana has been compared with that of comparison of A. thaliana and the even closer relative, many other species. This work has revealed a complex Capsella rubella, has shown extensive microsynteny (Acarhistory of genome-wide duplication and subsequent kan et al. 2000;Rossberg et al. 2001). However, the gene loss (Lan et al. 2000;Vision et al. 2000; Simillion closest relatives of A. thaliana have not been mapped et al. 2002). Even in rather remote relatives, such as rice, comparatively at the whole-genome level. tomato, and potato, syntenic stretches have been foundIn this article we construct a genetic map of A. lyrata, (Devos et al. 1999;Ku et al. 2000;Gebhardt et al. 2003).the closest relative of A. thaliana (Koch et al. 1999). This Comparisons with more closely related species have species is estimated to have diverged from A. thaliana shown that the rate of chromosomal evolution in the ‫5ف‬ MYA (Koch et al. 2000). The synonymous divergence Brassicaceae is quite rapid. Kowalski et al. (1994)

Chromosome triplication found across the tribe Brassiceae

“…Although our data strongly support the view that the structure of the ancestral genome prior to the presumed polyploidization event was similar to that of A. thaliana (Lagercrantz and Lydiate 1996;Lagercrantz 1998), the Arabidopsis karyotype is evolutionarily derived from an ancestral Capsellalike genome with eight linkage groups (Boivin et al 2004;Kuittinen et al 2004;. Thus, assuming an ancestral genome with n = 5 and yielding a hexaploid one with n = 15 chromosomes is not substantiated by the available data.…”

“…The At4-b contig spanning ∼8.7 Mb and corresponding ∼7% of the genome or nearly two-thirds of the bottom arm of Arabidopsis Chromosome 4 is comparatively mapped to the syntenic linkage groups G/6 and F/7 of Capsella rubella (Boivin et al 2004) and Arabidopsis lyrata (Kuittinen et al 2004), respectively. This contig was arbitrarily divided into three (A-C) differently labeled subcontigs ( Fig.…”

“…Although the karyotype of A. thaliana is a highly derived one (Boivin et al 2004;Kuittinen et al 2004;, the Arabidopsis-like structure of the ∼8.7-Mb region was found in species with a single copy of the At4-b contig (except in C. planisiliqua). Hence, this region remained apparently unchanged during at least 18 Mya since the divergence of Arabidopsis and Calepina and probably longer when considering that the Arabidopsis lineage was separated together with Lepidium (∼24 Mya) (Fig.…”

Transmission ratio distortion in Arabidopsis lyrata: effects of population divergence and the S-locus

“…Furthermore, it serves as a model for the evolution of sporophytic self-incompatibility systems (Kusaba et al, 2001;Schierup et al, 2001;Nasrallah et al, 2002;Bechsgaard et al, 2006). Kuittinen et al (2004) constructed a genetic map of A. lyrata by crossing individuals from two genetically diverged populations (Karhumäki, Russia and Mjällom, Sweden) that show substantial morphological and genetic differentiation (Nei's genetic distance estimated by different markers: 0.51 by Jonsell et al, 1995;0.39-0.51 by van Treuren et al, 1997 and 1.31 by Muller et al, 2007). Segregation patterns of about 50% of the molecular markers used to construct the map deviated significantly from Mendelian expectations.…”

“…We present data on the segregation of 14 microsatellites and 2 length polymorphisms in 8 of the families. Of these, 13 markers were also used in the interpopulation study by Kuittinen et al (2004).…”