Comparative Mapping and Rapid Karyotypic Evolution in the Genus Helianthus

Abstract

Comparative genetic linkage maps provide a powerful tool for the study of karyotypic evolution. We constructed a joint SSR/RAPD genetic linkage map of the Helianthus petiolaris genome and used it, along with an integrated SSR genetic linkage map derived from four independent H. annuus mapping populations, to examine the evolution of genome structure between these two annual sunflower species. The results of this work indicate the presence of 27 colinear segments resulting from a minimum of eight translocations and three inversions. These 11 rearrangements are more than previously suspected on the basis of either cytological or genetic map-based analyses. Taken together, these rearrangements required a minimum of 20 chromosomal breakages/fusions. On the basis of estimates of the time since divergence of these two species (750,000-1,000,000 years), this translates into an estimated rate of 5.5-7.3 chromosomal rearrangements per million years of evolution, the highest rate reported for any taxonomic group to date.

Evolution of reproductive isolation in plants

“…Rearrangements also contribute to the maintenance of reproductive isolation when parapatric sunflower species such as Helianthus annuus and H. petiolaris come into secondary contact (Rieseberg et al, 1999). Rearrangements between H. annuus and H. petiolaris accumulate at a rate of 5.5-7.3 per million years, the highest rate reported for any taxonomic group to date (Burke et al, 2004). Two observations support a role for rearrangements in the accumulation of genic isolating barriers between these two species.…”

Identification and mapping of SNPs from ESTs in sunflower

“…The RILs were developed by single-seed descent from the same two cultivars (RHA280 and RHA801) employed for the majority of EST sequencing. A dense map of anonymous markers already exists for this population Yu et al 2003); consequently, it has become the primary reference population for molecular breeding and comparative genomics research in sunflower (e.g., Burke et al 2004;Lai et al 2005). Ninety-four RILs from this cross were employed for population screening and map construction.…”

“…However, shortly thereafter several restriction fragment length polymorphism maps were published for the domesticated sunflower (Berry et al 1995;Gentzbittel et al 1995Gentzbittel et al , 1999Jan et al 1998), establishing a standard nomenclature for sunflower linkage groups and providing framework markers for comparisons among maps (Gedil et al 2001). More recently, high-resolution linkage maps based on more than 1,000 simple sequence repeat (SSR) and other sequence-tagged-site markers have been developed for the cultivated sunflower Yu et al 2003) and several wild species Burke et al 2004;Lai et al 2005).…”

Comparative linkage maps suggest that fission, not polyploidy, underlies near-doubling of chromosome number within monkeyflowers (Mimulus; Phrymaceae)

“…Comparative linkage mapping is a useful tool for the investigation of patterns of genome evolution, including chromosomal rearrangements, and also facilitates transfer of genetic tools and information among related but reproductively incompatible taxa (for examples, Burke et al, 2004;Wu and Tanksley, 2010). Both groups of monkeyflowers have been model systems for understanding speciation for nearly five decades and were among the first wild plants investigated with linkage and quantitative trait loci mapping approaches (Bradshaw et al, 1995;Fishman et al, 2001).…”