Patterns of domestication in the Ethiopian oil-seed crop noug (Guizotia abyssinica)

Noug (Guizotia abyssinica) is a semidomesticated oil-seed crop, which is primarily cultivated in Ethiopia. Unlike its closest crop relative, sunflower, noug has small seeds, small flowering heads, many branches, many flowering heads, and indeterminate flowering, and it shatters in the field. Here, we conducted common garden studies and microsatellite analyses of genetic variation to test whether high levels of crop–wild gene flow and/or unfavorable phenotypic correlations have hindered noug domestication. With the exception of one population, analyses of microsatellite variation failed to detect substantial recent admixture between noug and its wild progenitor. Likewise, only very weak correlations were found between seed mass and the number or size of flowering heads. Thus, noug's ‘atypical’ domestication syndrome does not seem to be a consequence of recent introgression or unfavorable phenotypic correlations. Nonetheless, our data do reveal evidence of local adaptation of noug cultivars to different precipitation regimes, as well as high levels of phenotypic plasticity, which may permit reasonable yields under diverse environmental conditions. Why noug has not been fully domesticated remains a mystery, but perhaps early farmers selected for resilience to episodic drought or untended environments rather than larger seeds. Domestication may also have been slowed by noug's outcrossing mating syste

The Genomic Signature of Crop-Wild Introgression in Maize

The evolutionary significance of hybridization and subsequent introgression has long been appreciated, but evaluation of the genome-wide effects of these phenomena has only recently become possible. Crop-wild study systems represent ideal opportunities to examine evolution through hybridization. For example, maize and the conspecific wild teosinte Zea mays ssp. mexicana, (hereafter, mexicana) are known to hybridize in the fields of highland Mexico. Despite widespread evidence of gene flow, maize and mexicana maintain distinct morphologies and have done so in sympatry for thousands of years. Neither the genomic extent nor the evolutionary importance of introgression between these taxa is understood. In this study we assessed patterns of genome-wide introgression based on 39,029 single nucleotide polymorphisms genotyped in 189 individuals from nine sympatric maize-mexicana populations and reference allopatric populations. While portions of the maize and mexicana genomes were particularly resistant to introgression (notably near known cross-incompatibility and domestication loci), we detected widespread evidence for introgression in both directions of gene flow. Through further characterization of these regions and preliminary growth chamber experiments, we found evidence suggestive of the incorporation of adaptive mexicana alleles into maize during its expansion to the highlands of central Mexico. In contrast, very little evidence was found for adaptive introgression from maize to mexicana. The methods we have applied here can be replicated widely, and such analyses have the potential to greatly informing our understanding of evolution through introgressive hybridization. Crop species, due to their exceptional genomic resources and frequent histories of spread into sympatry with relatives, should be particularly influential in these studies

Position and sequence conservation in Amniota of polymorphic enhancer HS1.2 within the palindrome of IgH 3'Regulatory Region

<p>Abstract</p> <p>Background</p> <p>The Immunoglobulin heavy chain (IgH) 3' Regulatory Region (3'RR), located at the 3' of the constant alpha gene, plays a crucial role in immunoglobulin production. In humans, there are 2 copies of the 3'RR, each composed of 4 main elements: 3 enhancers and a 20 bp tandem repeat. The single mouse 3'RR differs from the two human ones for the presence of 4 more regulative elements with the double copy of one enhancer at the border of a palindromic region.</p> <p>Results</p> <p>We compared the 3'RR organization in genomes of vertebrates to depict the evolutionary history of the region and highlight its shared features. We found that in the 8 species in which the whole region was included in a fully assembled contig (mouse, rat, dog, rabbit, panda, orangutan, chimpanzee, and human), the shared elements showed synteny and a highly conserved sequence, thus suggesting a strong evolutionary constraint. In these species, the wide 3'RR (~30 kb in human) bears a large palindromic sequence, consisting in two ~3 kb complementary branches spaced by a ~3 kb sequence always including the HS1.2 enhancer. In mouse and rat, HS3 is involved by the palindrome so that one copy of the enhancer is present on each side. A second relevant feature of our present work concerns human polymorphism of the HS1.2 enhancer, associated to immune diseases in our species. We detected a similar polymorphism in all the studied Catarrhini (a primate parvorder). The polymorphism consists of multiple copies of a 40 bp element up to 12 in chimpanzees, 8 in baboons, 6 in macaque, 5 in gibbons, 4 in humans and orangutan, separated by stretches of Cytosine. We show specific binding of this element to nuclear factors.</p> <p>Conclusions</p> <p>The nucleotide sequence of the palindrome is not conserved among evolutionary distant species, suggesting pressures for the maintenance of two self-matching regions driving a three-dimensional structure despite of the inter-specific divergence at sequence level. The information about the conservation of the palindromic structure and the settling in primates of the polymorphic feature of HS1.2 show the relevance of these structures in the control and modulation of the Ig production through the formation of possible three-dimensional structures.</p

Nondisjunction rates of mouse specific chromosomes involved in heterozygous Rb rearrangements measured by chromosome painting of spermatocytes II. I. The effects of the number of trivalents

Dual-colour FISH painting with alternative fluorescent chromosome-specific probes allowed us to distinguish chromosomes 1, 4, 6 and 14. The purpose was to check whether nondisjunction rates of specific chromosomes involved in heterozygous Robertsonian fusions are independent of the number of trivalents, or an epistatic effect among Rb chromosomes takes place affecting nondisjunction rates. Probes were used on DAPI-stained metaphases of spermatocytes II of laboratory strains of mice with reconstructed karyotypes heterozygous for one, two, three or four Robertsonian metacentrics in an all-acrocentric background. The existence of such epistatic interactions was not verified. Copyright © 2003 S. Karger AG, Basel

Non disjunction rates of mouse chromosomes involved in heterozygous Rb rearrangements measured by chromosome painting of spermatocytes. II. The effects of trivalent combinations and genetic background

Chromosome specific nondisjunction rates were quantified by dual-colour FISH in spermatocytes II of Robertsonian heterozygous mice with different trivalent combinations or, alternatively, with different genetic backgrounds. We found that such factors do not influence the proneness to nondisjunction of specific chromosomes

Nondisjunction rates of mouse specific chromosomes involved in heterozygouus Rb rerarrangements measured by chromosome painting of spermatocytes II. I. The effects of the number of trivalents

Mediante dual-colour FISH painting, è riisultato possibile distinguere i diversi cromosomi negli spermatociti II di eterozigoti per traslocazioni Robertsoniane in Mus musculus. E' stata così dimostrata l'assenza di effetti epistatici per quanto riguarda la non disgiunzione dei diversi trivalenti