title: Structural differences in chromosomes distinguish species in the tomato clade.
abstract: The tomato clade of Solanaceae is composed of 12 species that are all diploid with the same chromosome number and morphology. Species in the tomato clade are considered to have evolved primarily by genic changes rather than large-scale chromosomal rearrangements because pachytene chromosomes in F(1) hybrids synapse normally along their lengths and linkage maps of intra- and inter-specific hybrids are co-linear. However, small inversions have been reported between tomato and some of its wild relatives. Therefore, we reevaluated 5 F(1) hybrids using high-resolution, electron microscopic examination of pachytene chromosome (= synaptonemal complex) spreads to determine whether any minor structural changes had occurred among species in the tomato clade, which were not easily visible using light microscopic analysis of conventional chromosome squashes. Our study revealed a number of unexpected synaptic configurations such as mismatched kinetochores, inversion loops and reciprocal translocations. Most of these structural differences were in or close to heterochromatin that has comparatively few genes and little recombination, so they would be expected to have little effect on the evident colinearity of linkage maps, especially in euchromatin. However, these results demonstrate that substantial changes in chromosome structure have occurred among species within the tomato clade.
authors.affiliation: Department of Biology and Program in Plant Molecular Biology, Colorado State University, Fort Collins, CO 80523-1878, USA. lorinda.anderson@colostate.edu
authors.forename: L K
authors.initials: LK
authors.lastname: Anderson
authors.forename: P A
authors.initials: PA
authors.lastname: Covey
authors.forename: L R
authors.initials: LR
authors.lastname: Larsen
authors.forename: P
authors.initials: P
authors.lastname: Bedinger
authors.forename: S M
authors.initials: SM
authors.lastname: Stack
mesh_terms: D005075:Biological Evolution; D023902:Chromosome Pairing; D032461:Chromosomes, Plant / Q000235:genetics* / Q000648:ultrastructure*; D018744:DNA, Plant / Q000235:genetics; D018745:Genome, Plant; D006824:Hybridization, Genetic; D017404:In Situ Hybridization, Fluorescence; D018551:Solanum lycopersicum / Q000145:classification* / Q000235:genetics* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010802:Phylogeny; D019657:Solanaceae / Q000145:classification* / Q000235:genetics* / Q000648:ultrastructure; D013045:Species Specificity; D013573:Synaptonemal Complex / Q000235:genetics / Q000648:ultrastructure
chemical_list: D018744:DNA, Plant