Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing.     

2-Phenylethylamine catabolism by Escherichia coli K12

Escherichia coli K12 grows on 2-phenylethylamine as sole carbon and energy source by converting it, via phenylacetaldehyde, to phenylacetic acid. Phenylacetaldehyde was formed by the action of an inducible amine oxidase and catalase activity was increased sixfold, presumably to ensure removal of the H2O2 that was expected to be a product of the amine oxidation. The phenylacetaldehyde was oxidized to phenylacetic acid by an inducible NAD+-dependent dehydrogenase. Mutants defective in phenylacetaldehyde dehydrogenase cannot grow on 2-phenylethylamine as carbon and energy source but can still use it as a nitrogen source.     

Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

Identification of quantitative trait loci for plant height, lodging, and maturity in a soybean population segregating for growth habit

The use of molecular markers to identify quantitative trait loci (QTLs) has the potential to enhance the efficiency of trait selection in plant breeding. The purpose of the present study was to identify additional QTLs for plant height, lodging, and maturity in a soybean, Glycine max (L.) Merr., population segregating for growth habit. In this study, 153 restriction fragment length polymorphisms (RFLP) and one morphological marker (Dt1) were used to identify QTLs associated with plant height, lodging, and maturity in 111 F₂-derived lines from a cross of PI 97100 and Coker 237. The F₂-derived lines and two parents were grown at Athens, Ga., and Blackville, S.C., in 1994 and evaluated for phenotypic traits. The genetic linkage map of these 143 loci covered about 1600 cM and converged into 23 linkage groups. Eleven markers remained unlinked. Using interval-mapping analysis for linked markers and single-factor analysis of variance (ANOVA), loci were tested for association with phenotypic data taken at each location as well as mean values over the two locations. In the combined analysis over locations, the major locus associated with plant height was identified as Dt1 on linkage group (LG) L. The Dt1 locus was also associated with lodging. This locus explained 67.7% of the total variation for plant height, and 56.4% for lodging. In addition, two QTLs for plant height (K007 on LG H and A516b on LG N) and one QTL for lodging (cr517 on LG J) were identified. For maturity, two independent QTLs were identified in intervals between R051 and N100, and between B032 and CpTI, on LG K. These QTLs explained 31.2% and 26.2% of the total variation for maturity, respectively. The same QTLs were identified for all traits at each location. This consistency of QTLs may be related to a few QTLs with large effects conditioning plant height, lodging, and maturity in this population.     

Molecular markers associated with seed weight in two soybean populations

Seed weight (SW) is a component of soybean, Glycine max (L.) Merr., seed yield, as well as an important trait for food-type soybeans. Two soybean populations, 120 F₄-derived lines of YoungxPI416937 (Pop1) and 111 F₂-derived lines of PI97100xCoker 237 (Pop2), were mapped with RFLP makers to identify quantitative trait loci (QTLs) conditioning SW across environments and populations. The genetic map of Pop1 consisted of 155 loci covering 973 cM, whereas Pop2 involved 153 loci and covered 1600 cM of map distance. For Pop1, the phenotypic data were collected from Plains, GA., Windblow, N.C., and Plymouth, N.C., in 1994. For Pop2, data were collected from Athens, GA., in 1994 and 1995, and Blackville, S.C., in 1995. Based on single-factor analysis of variance (ANOVA), seven and nine independent loci were associated with SW in Pop1 and Pop2, respectively. Together the loci explained 73% of the variability in SW in Pop1 and 74% in Pop2. Transgressive segregation occurred among the progeny in both populations. The marker loci associated with SW were highly consistent across environments and years. Two QTLs on linkage group (LG) F and K were located at similar genomic regions in both populations. The high consistency of QTLs across environments indicates that effective marker-assisted selection is feasible for soybean SW.     

Characterization of recurrent somatic embryogenesis of alfalfa on auxin-free medium

Callus cultures from 300 genotypes of alfalfa (Medicago sativa L.) were initiated from leaf, petiole, and internode explants placed on Blaydes medium containing 10.74 M -naphthaleneacetic acid, 11.42 M indole-3-acetic acid, and 9.29 M kinetin. Five genotypes produced somatic embryos. Upon transfer of these embryos to growth regulator-free Murashige and Skoog medium with B₅ vitamins, new somatic embryos repeatedly formed directly on older somatic embryos without an intervening callus phase in a cycle lasting about 30 days. These cultures have been maintained for two years, during which time their embryogenic capacity has remained stable. New embryogenic cultures could be started repeatedly from these genotypes. The elimination of sugars from the medium could stop recurrent embryogenesis. Glucose, maltose, and fructose stimulated recurrent embryogenesis more effectively than sucrose. Sucrose was superior to lactose, while sorbitol and mannitol did not stimulate recurrent somatic embryogenesis. The absence of nicotinic acid in the medium, as long as sucrose was present, was lethal to embryos of three of the five tested genotypes. The ability of this system to propagate embryos exponentially offers potential for development of new gene transfer systems and application to artificial seed technology.Abbreviations NAA -naphthaleneacetic acid - RSE recurrent somatic embryogenesis     

Recovery and evaluation of soybean plants transgenic for aBacillus thuringiensis var.Kurstaki insecticidal gene

Summary Lepidopteran insects are major defoliating pests of soybean in the southeastern United States. Soybean plants transgenic for a nativecryIA(b) gene fromBacillus thuringiensis var.kurstaki HD-1 were obtained. Embryogenic cultures were induced by plating cotyledons on a Murashige and Skoog-based medium supplemented with 40 mg/liter of 2,4-dichlorophenoxyacetic acid (2,4-D). The embryogenic cultures were maintained in liquid medium containing 5 mg/liter 2,4-D. These cultures were subjected to microprojectile bombardment, followed by selection on 50 mg/liter hygromycin. Resistant embryogenic cell lines were transferred to growth regulator-free medium to permit recovery of mature somatic embryos. After a desiccation period, the somatic embryos were returned to growth regulator-free medium for conversion into plants. Southern hybridization analysis verified transformation. Feeding assays of T₁ plants from one cell line deterred feeding, development, and survival of velvetbean caterpillar at a level comparable to that of GatIR81-296, a soybean breeding line with a high level of insect resistance. Reduced feeding on T₁ plants correlated with the presence of the transgene.     

Development of DNA methylation-based epigenetic age predictors in loblolly pine (Pinus taeda)

Biological ageing is connected to life history variation across ecological scales and informs a basic understanding of age-related declines in organismal function. Altered DNA methylation dynamics are a conserved aspect of biological ageing and have recently been modelled to predict chronological age among vertebrate species. In addition to their utility in estimating individual age, differences between chronological and predicted ages arise due to acceleration or deceleration of epigenetic ageing, and these discrepancies are linked to disease risk and multiple life history traits. Although evidence suggests that patterns of DNA methylation can describe ageing in plants, predictions with epigenetic clocks have yet to be performed. Here, we resolve the DNA methylome across CpG, CHG, and CHH-methylation contexts in the loblolly pine tree (Pinus taeda) and construct epigenetic clocks capable of predicting ages in this species within 6% of its maximum lifespan. Although patterns of CHH-methylation showed little association with age, both CpG and CHG-methylation contexts were strongly associated with ageing, largely becoming hypomethylated with age. Among age-associated loci were those in close proximity to malate dehydrogenase, NADH dehydrogenase, and 18S and 26S ribosomal RNA genes. This study reports one of the first epigenetic clocks in plants and demonstrates the universality of age-associated DNA methylation dynamics which can inform conservation and management practices, as well as our ecological and evolutionary understanding of biological ageing in plants.