Effect of selection on the heterozygosity of inbred lines of maize

Although pedigree selection is the most commonly used method for developing inbred lines of maize, there are no studies on its effect on the heterozygosity of the lines. The objective of this work was to study the effect of pedigree selection on their heterozygosity. Thirteen F₅ or F₆ maize inbred lines developed by the pedigree selection method in four breeding programs and their F₁ and F₂ − F₄ ancestors were genotyped with simple sequence repeat markers distributed along the genome. Simulation was also conducted assuming different models of selection to investigate the selective forces needed to explain the data. In the F₂, F₃ and F₄ 40%, 66% and 86% of the markers segregating in the F₁ were fixed; that is, in the F₂ and F₃ fixation was lower than neutral expectation, but higher in the F₄. Due to such opposite apparent directions of selection, the heterozygosity of the lines in the F₅ or F₆ generations did not differ significantly from neutral expectations. The time to fixation differed from that expected with neutrality for most of the chromosomes, indicating that selection is distributed across the genome; but apparent overdominant effects in chromosome 7 were higher than in other chromosomes. In conclusion, the relationship between heterozygosity and vigour may reduce the effectiveness of pedigree selection in its goal of selecting the more vigorous, homozygous individuals. A more effective procedure is proposed using molecular markers for the identification of the more homozygous individuals, the most vigorous of those individuals being selected.     

Intracellular ATP in a glucosephosphate isomerase mutant ofSaccharomyces cerevisiae

The degree of ATP depletion caused by glucose in a glucosephosphate isomerase-deficient strain of Saccharomyces cerevisiae was determined. Even in the presence of a sugar normally fermentable by the mutant, the addition of glucose can decrease the intracellular ATP, depending on the competition of the sugars for transport and subsequent phosphorylation. For both parent and mutant cells, a correlation exists between the calculated velocity of ATP formation or ATP consumption during the utilization of different concentrations of sugars and the experimental intracellular ATP level. For initially resting yeast cells, a rate increase of 35 mumol per min per g ATP was calculated to increase the intracellular level of this nucleotide by 1 mumol per g cell mass.     

Ceramide accumulation mediates inflammation, cell death and infection susceptibility in cystic fibrosis

Microbial lung infections are the major cause of morbidity and mortality in the hereditary metabolic disorder cystic fibrosis, yet the molecular mechanisms leading from the mutation of cystic fibrosis transmembrane conductance regulator (CFTR) to lung infection are still unclear. Here, we show that ceramide age-dependently accumulates in the respiratory tract of uninfected Cftr-deficient mice owing to an alkalinization of intracellular vesicles in Cftr-deficient cells. This change in pH results in an imbalance between acid sphingomyelinase (Asm) cleavage of sphingomyelin to ceramide and acid ceramidase consumption of ceramide, resulting in the higher levels of ceramide. The accumulation of ceramide causes Cftr-deficient mice to suffer from constitutive age-dependent pulmonary inflammation, death of respiratory epithelial cells, deposits of DNA in bronchi and high susceptibility to severe Pseudomonas aeruginosa infections. Partial genetic deficiency of Asm in Cftr(-/-)Smpd1(+/-) mice or pharmacological treatment of Cftr-deficient mice with the Asm blocker amitriptyline normalizes pulmonary ceramide and prevents all pathological findings, including susceptibility to infection. These data suggest inhibition of Asm as a new treatment strategy for cystic fibrosis.     

Antioxidant properties of alpha-crystallin

-Crystallin is a major chaperone lens protein to which has been ascribed antioxidant functions. In the present work we have evaluated the antioxidant and free radical scavenging properties of bovine -crystallin in a series of in vitro models: zimosan-induced, luminol-enhanced chemiluminescence response of polymorphonuclear leukocytes, the autoxidation of brain homogenate, bleaching of 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)-derived radical cations, trapping of peroxyl radicals, and reactivity toward hypochloric acid. In all these systems, the reactivity of -crystallin is higher than or similar to that of bovine serum albumin. It is concluded that, given the high concentrations of -crystallin in the lenses, its capacity to interact with free radicals and to remove hypochlorous acid could contribute to the maintenance of the lens functionality.     

Joint analysis of days to flowering reveals independent temperate adaptations in maize

Domesticates are an excellent model for understanding biological consequences of rapid climate change. Maize (Zea mays ssp. mays) was domesticated from a tropical grass yet is widespread across temperate regions today. We investigate the biological basis of temperate adaptation in diverse structured nested association mapping (NAM) populations from China, Europe (Dent and Flint) and the United States as well as in the Ames inbred diversity panel, using days to flowering as a proxy. Using cross-population prediction, where high prediction accuracy derives from overall genomic relatedness, shared genetic architecture, and sufficient diversity in the training population, we identify patterns in predictive ability across the five populations. To identify the source of temperate adapted alleles in these populations, we predict top associated genome-wide association study (GWAS) identified loci in a Random Forest Classifier using independent temperate–tropical North American populations based on lines selected from Hapmap3 as predictors. We find that North American populations are well predicted (AUC equals 0.89 and 0.85 for Ames and USNAM, respectively), European populations somewhat well predicted (AUC equals 0.59 and 0.67 for the Dent and Flint panels, respectively) and that the Chinese population is not predicted well at all (AUC is 0.47), suggesting an independent adaptation process for early flowering in China. Multiple adaptations for the complex trait days to flowering in maize provide hope for similar natural systems under climate change.Subject terms: Evolutionary genetics, Quantitative trait     

Genetic and environmental factors reducing the incidence of the storage pest Sitotroga cerealella in maize

The Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), is found worldwide and infests maize grains in the field and during storage. Transgenic maize resistant to kernel attack by S. cerealella has been developed, but could pose a nutritional risk to humans and livestock. Therefore, alternative sources of resistance posing no threat to consumption should be identified. In this study, our main objectives were to assess genetic variability for kernel damage by S. cerealella under natural infestation and to determine genetic and environmental factors contributing to genotype, year, and genotype*year variability. Factorial regression was performed to obtain a biological explanation for the number of kernels damaged per ear. Seventy-seven Spanish maize landraces along with six hybrid checks were evaluated in 2004, 2005, and 2006. There was variability for kernel damage by natural infestation of S. cerealella among the landraces: popcorn landraces were among the least damaged, whereas hybrid checks were among the most susceptible genotypes. Plant characteristics associated with ear appearance could be the main stimulatory factors for oviposition and feeding of S. cerealella moths, followed by husk coverage of the ear. It was confirmed that temperature is the main environmental factor affecting S. cerealella development. Genotypes sensitive to infestation by S. cerealella were more negatively affected by higher temperatures than the least attractive genotypes, and lower temperatures reduced the number of kernels damaged on the most susceptible genotypes more than on the least susceptible.