Guest Artist Series: Dennis Bubert, Bass Trombone; Nan McSwain, Piano; April 8, 2004

Center for the Performing ArtsThursday EveningApril 8, 20048:00 p.m

Linkage of Bacterial Protein Synthesis and Presentation of MHC Class I-Restricted Listeria monocytogenes-Derived Antigenic Peptides

The processing and MHC class I-restricted presentation of antigenic peptides derived from the p60 protein of the facultative intracellular bacterium Listeria monocytogenes is tightly linked to bacterial protein synthesis. We used non-linear regression analysis to fit a mathematical model of bacterial antigen processing to a published experimental data set showing the accumulation and decay of p60-derived antigenic peptides in L. monocytogenes-infected cells. Two alternative models equally describe the experimental data. The simulation accounting for a stable and a hypothetical rapidly degraded form of antigen predicts that the antigenic peptides p60 217–225 and p60 449–457 are derived from a putative instable form of p60 with an average intracellular half-life of approximately 3 minutes accounting for approximately 31% of all p60 molecules synthesized. The alternative model predicts that both antigenic peptides are processed from p60 degraded intracellularly with a half-life of 109 min and that antigen processing only occurs as long as bacterial protein synthesis is not inhibited. In order to decide between both models the intracellular accumulation of p60 in infected cells was studied experimentally and compared with model predictions. Inhibition of p60 degradation by the proteasome inhibitor epoxomicin revealed that during the first 3 h post infection approximately 30% of synthesized p60 molecules were degraded. This value is significantly lower than the approximately 50% degradation of p60 that would be expected in the presence of the predicted putative short-lived state of p60 and also fits precisely with the predictions of the alternative model, indicating that the tight connection of bacterial protein biosynthesis and antigen processing and presentation of L. monocyctogenes-derived antigenic peptides is not caused by the presence of a highly instable antigenic substrate

Genomic improvement of nitrogen utilization efficiency in maize

As available land for agricultural production has stabilized, farmers rely on fertilizer application rates to boost yields. Consequently, nitrogen (N) use in the United States has increased nearly six fold in the last fifty years to more than 13 million tons applied in 2014, an increase that mirrors worldwide trends. The production of N fertilizer is dependent on energy inputs to convert atmospheric dinitrogen to a form useable by plants, so as energy prices continue to climb the cost of N fertilizers will increase accordingly. Additionally, the detrimental environmental effects on water and air quality of nitrogen losses from denitrification, volatilization, and leaching are well documented. As such, improvements to nitrogen use efficiency (NUE) is an important target for future maize breeding efforts. The objectives of this research were to assess existing phenotypic and genotypic variation for NUE related traits, and leverage that variation to understand and improve hybrid performance. Historical and elite germplasm were grown as inbreds and hybrids in highly managed multi-year field trials under varying rates of applied nitrogen. Preliminary results supported previous research demonstrating N uptake efficiency may already be optimized, but there are opportunities to improve N utilization efficiency (NUtE). Field based trials were subjected to a phenotyping pipeline that estimates N utilization as a ratio of total biomass to total plant N. Measuring total NUtE on both hybrids and their inbred parents effectively controls for the impacts of relative maturity and heterosis on this trait. The results of this research indicate that available soil N in this geographical region is typically sufficient for inbreds to reach sink capacity, thereby limiting nitrogen response to supplemental N in inbreds. The lack of N response in inbreds indicates that making selections for NUtE in inbreds per se will not result in efficient genetic gain. Hybrids showed a consistent N response but do have a significant tester effect, so future research to understand the genetic mechanisms of heterosis is necessary in order to account for the hybrid combinations used in NUtE trials. The diversity that was identified through field testing and NUtE phenotyping was sufficient to support the use of genomic tools to increase NUtE in maize. Among many quantitative trait loci (QTL) detected in a prior genetic mapping experiment, nine robust intervals were determined to account for 5-15% of variation for multiple nitrogen utilization traits across years. The contribution of these previously identified QTL to NUtE among diverse maize hybrids was assessed using a genome-wide association study. Three of the nine QTL had significant marker-trait associations within their boundaries and an additional 12-24 significant SNPs were identified for NUtE related traits that may provide additional genes of interest that were not captured by the IBM mapping population used for QTL analysis. A genomic prediction approach was used to capture small genetic effects across the genome. Within year prediction accuracies for genomic prediction of grain nitrogen were 0.5 when the training population is 30% of the total population, while between-year accuracies with a one year training set were 0.28. Between year genomic predictions of hybrids using inbred data as a training set were 0.37 and 0.49 for NUtE and grain biomass, respectively. Similar to predictions of hybrid performance from inbred phenotypes, the ability to predict hybrid performance from inbred genotypes could be improved with a better understanding of the genetic mechanisms underlying heterosis. Including multi-year phenotypes in the training set and expanding the model beyond just additive effects could also significantly improve prediction accuracies in the future. It has long been known that heterosis is related to the degree of heterozygosity in a hybrid and recent advances in genome-scale genotyping enable detailed estimates of heterozygosity. Thus, in an effort to understand the genetic mechanisms underlying heterosis and how they impact complex traits, we conducted an experiment to investigate the influence of heterozygosity on nitrogen utilization efficiency and its component traits. Analysis of single nucleotide polymorphism (SNP) markers in more than 400 maize genes enriched for regulatory functions and control of N utilization showed divergent selection among the major germplasm groups for temperate maize production, indicating that heterozygosity is a preferred breeding goal to maximize N utilization and yield. In order to further test this preference, populations were created to maximize heterozygosity at three different levels: across the whole genome, within the previously known nine QTL regions, and at the SNP locations within the QTL that are also divergent between heterotic groups. Field testing of the populations for NUtE related traits indicated that heterozygosity is a preferred germplasm state for hybrid performance for grain biomass, stover biomass, and grain N. Additionally, selection for heterozygosity on a limited number of informed SNP markers can provide the same level of heterosis as selecting across the entire genome. This understanding of the importance of heterozygosity will be useful in guiding the selection of inbred parents to create future hybrids with better NUtE

Spectroscopic investigations of a Ti:Tm:LiNbO3 waveguide for photon-echo quantum memory

We report the fabrication and characterization of a Ti$^{4+}$:Tm$^{3+}$:LiNbO$_3$ optical waveguide in view of photon-echo quantum memory applications. In particular, we investigated room- and cryogenic-temperature properties via absorption, spectral hole burning, photon echo, and Stark spectroscopy. We found radiative lifetimes of 82 $\mu$s and 2.4 ms for the $^3$H$_4$ and $^3$F$_4$ levels, respectively, and a 44% branching ratio from the $^3$H$_{4}$ to the $^3$F$_4$ level. We also measured an optical coherence time of 1.6 $\mu$s for the $^3$H$_6\leftrightarrow{}^3$H$_4$, 795 nm wavelength transition, and investigated the limitation of spectral diffusion to spectral hole burning. Upon application of magnetic fields of a few hundred Gauss, we observed persistent spectral holes with lifetimes up to seconds. Furthermore, we measured a linear Stark shift of 25 kHz$\cdot$cm/V. Our results are promising for integrated, electro-optical, waveguide quantum memory for photons.Comment: 11 pages, 14 figure

Produção chilena de Molibdênio: Influência no mercado mundial e seu comportamento exportador (2007-2016)

Chile is a leader in the global molybdenum industry, however, there are no studies related to the modeling of the exporting behavior. We study the Chilean export behavior of molybdenum during the period 2007-2016 and detect the variables that influence it. In addition, the effect of trade relations, free trade agreements, trade facilitation and logistics is identified. To model the exporting behavior of molybdenum, an expanded gravitational model is applied to the reality of the Chilean bilateral trade and the world market of molybdenum. The raised model follows a pattern that corresponds to Dynamic panel data.Chile es líder en la industria mundial de molibdeno, sin embargo, no se observan estudios relacionados con la modelación del comportamiento exportador. Se estudia el comportamiento exportador chileno del molibdeno durante el período 2007-2016 y detectan las variables que influyen en él. Adicionalmente, se identifica el efecto de las relaciones comerciales, tratados de libre comercio, facilitación comercial y logística. Para modelar el comportamiento exportador de molibdeno se aplica un modelo gravitacional ampliado a la realidad del comercio bilateral chileno y mercado mundial del molibdeno. El modelo planteado sigue un patrón que corresponde a datos de panel dinámicos.O Chile é líder na indústria de molibdênio, no entanto, não se observam estudos relacionados com a modelação do comportamento exportador. Estuda-se o comportamento exportador chileno do molibdênio durante o período 2007-2016 e detectam as variáveis que influem nele. Adicionalmente, identifica-se o efeito das relações comerciais, tratados de livre comércio, facilitação comercial e logística. Para modelar o comportamento exportador de molibdênio aplica-se um modelo gravitacional ampliado à realidade do comercio bilateral chileno e mercado mundial do molibdênio. O modelo apresentado segue um patrão que corresponde a dados de painel dinâmico