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 F₁ 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 F₁ 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.

Identification of resistance to Bemisia tabaci Genn. in closely related wild relatives of cultivated tomato based on trichome type analysis and choice and no-choice assays

“…Durable whitefly resistance, especially in the field, is more likely if tomato cultivars mount resistance based on a combination of antixenosis and antibiosis factors, thus forcing whiteflies to surmount a wide range of plant defenses (Anderson et al 2010;Broekgaarden et al 2011;Zangerl and Rutledge 1996). Capacity to repel and avoid whitefly landing, probing, and feeding is important to thwart whitefly as a vector of plant viruses, especially begomoviruses.…”

Genome Structure of the Heavy Metal Hyperaccumulator Noccaea caerulescens and Its Stability on Metalliferous and Nonmetalliferous Soils

“…), paracentric inversions were observed more frequently than pericentric ones (Coyne et al, 1991(Coyne et al, , 1993Kirkpatrick, 2010;Auger and Sheridan, 2012). One reason is that small pericentric inversions frequently formed within heterochromatin-rich and low-recombining pericentromeric regions are difficult to detect by genetic mapping or conventional chromosomal analyses (Anderson et al, 2010). Despite being less frequently reported, many pericentric inversions do not need to be underdominant if recombination is suppressed in inverted regions, as shown in Drosophila spp.…”

Genetic diversity of cultivated and wild tomatoes revealed by morphological traits and SSR markers

“…These species in the tomato clade are all diploid with the same chromosome number (2n = 24) and are considered to have evolved primarily by genic changes rather than large-scale chromosomal rearrangements (Anderson et al, 2010). The wild species of tomato harbor many valuable genes, which may have been lost among cultivated tomatoes.…”