1,206 research outputs found

    Enzymes from Fungal and Plant Origin Required for Chemical Diversification of Insecticidal Loline Alkaloids in Grass-\u3cem\u3eEpichloë\u3c/em\u3e Symbiota

    Get PDF
    The lolines are a class of bioprotective alkaloids that are produced by Epichloë species, fungal endophytes of grasses. These alkaloids are saturated 1-aminopyrrolizidines with a C2 to C7 ether bridge, and are structurally differentiated by the various modifications of the 1-amino group: -NH2 (norloline), -NHCH3 (loline), -N(CH3)2 (N-methylloline), -N(CH3)Ac (N-acetylloline), -NHAc (N-acetylnorloline), and -N(CH3)CHO (N-formylloline). Other than the LolP cytochrome P450, which is required for conversion of N-methylloline to N-formylloline, the enzymatic steps for loline diversification have not yet been established. Through isotopic labeling, we determined that N-acetylnorloline is the first fully cyclized loline alkaloid, implying that deacetylation, methylation, and acetylation steps are all involved in loline alkaloid diversification. Two genes of the loline alkaloid biosynthesis (LOL) gene cluster, lolN and lolM, were predicted to encode an N-acetamidase (deacetylase) and a methyltransferase, respectively. A knockout strain lacking both lolN and lolM stopped the biosynthesis at N-acetylnorloline, and complementation with the two wild-type genes restored production of N-formylloline and N-acetylloline. These results indicated that lolN and lolM are required in the steps from N-acetylnorloline to other lolines. The function of LolM as an N-methyltransferase was confirmed by its heterologous expression in yeast resulting in conversion of norloline to loline, and of loline to N-methylloline. One of the more abundant lolines, N-acetylloline, was observed in some but not all plants with symbiotic Epichloë siegelii, and when provided with exogenous loline, asymbiotic meadow fescue (Lolium pratense) plants produced N-acetylloline, suggesting that a plant acetyltransferase catalyzes N-acetylloline formation. We conclude that although most loline alkaloid biosynthesis reactions are catalyzed by fungal enzymes, both fungal and plant enzymes are responsible for the chemical diversification steps in symbio

    Civil conflict, federalism and strategic delegation of leadership

    Get PDF
    This article analyzes negative externalities that policymakers in one region or group may impose upon the citizens of neighboring regions or groups. These externalities may be material, but they may also be psychological (in the form of envy). The latter form of externality may arise from the production of 'conspicuous' public goods. As a result, decentralized provision of conspicuous public goods may be too high. Potentially, a centralized legislature may internalize negative externalities. However, in a model with strategic delegation, we argue that the median voter in each jurisdiction may anticipate a reduction in local public goods supply and delegate to a policymaker who cares more for public goods than she does herself. This last effect mitigates the expected benefits of policy centralization. The authors' theory is then applied to the setting of civil conflict, where they discuss electoral outcomes in Northern Ireland and Yugoslavia before and after significant institutional changes that affected the degree of centralization. These case studies provide support for the authors' theoretical predictions

    Exploring CP Violation through Correlations in B --> pi K, B_d --> pi^+pi^-, B_s --> K^+K^- Observable Space

    Full text link
    We investigate allowed regions in observable space of B --> pi K, B_d --> pi^+pi^- and B_s --> K^+K^- decays, characterizing these modes in the Standard Model. After a discussion of a new kind of contour plots for the B→πKB\to\pi K system, we focus on the mixing- induced and direct CP asymmetries of the decays B_d --> pi^+pi^- and B_s--> K^+K^-. Using experimental information on the CP-averaged B_d --> pi^{+/-}K^{+/-} and B_d --> pi^+pi^- branching ratios, the relevant hadronic penguin parameters can be constrained,implying certain allowed regions in observable space. In the case of B_d --> pi^+pi^-, an interesting situation arises now in view of the recent B-factory measurements of CP violation in this channel, allowing us to obtain new constraints on the CKM angle gamma as a function of the B^0_d--\bar{B^0_d} mixing phase phi_d=2beta, which is fixed through A_{CP}^{mix}(B_d --> J/psi K_S) up to a twofold ambiguity. If we assume that A_{CP}^{mix}(B_d --> pi^+pi^-) is positive, as indicated by recent Belle data, and that phi_d is in agreement with the ``indirect'' fits of the unitarity triangle, also the corresponding values for gamma around 60 degrees can be accommodated. On the other hand, for the second solution of phi_d, we obtain a gap around gamma ~ 60 degrees. The allowed region in the space of A_{CP}^{mix}(B_s --> K^+K^-) and A_{CP}^{dir}(B_s --> K^+K^-) is very constrained in the Standard Model, thereby providing a narrow target range for run II of the Tevatron and the experiments of the LHC era.Comment: 34 pages, LaTeX, 12 figures. More detailed introduction and a few Comments added, conclusions unchanged. To appear in Phys. Rev.

    CP violating polarizations in semileptonic heavy meson decays

    Full text link
    We study the TT-violating lepton transverse polarization (Pl⊥P^\perp_l) in three body semileptonic heavy meson decays to pseudoscalar mesons and to vector mesons. We calculate these polarizations in the heavy quark effective limit, which simplifies the expressions considerably. After examining constraints from CPCP conserving (including b→sγb \rightarrow s \gamma) and CPCP violating processes, we find that in BB decays, P⊥P^\perp of the muon in multi-Higgs doublet models can be of order 10%10\%, while P⊥P^\perp of the τ\tau can even approach unity. In contrast, Pμ⊥P^\perp_\mu in DD decays is at most 1.5\%. We discuss possibilities for detection of Pl⊥P^\perp_l at current and future BB factories. We also show that Pl⊥P^\perp_l in decays to vector mesons, unlike in decays to pseudoscalars, can get contributions from left-right models. Unfortunately, Pl⊥P^\perp_l in that case is proportional to WLW_L-WRW_R mixing, and is thus small.Comment: 32pp plain LATEX, 3 figs (by EMAIL request), TRI-PP-94-1

    Ether Bridge Formation in Loline Alkaloid Biosynthesis

    Get PDF
    Lolines are potent insecticidal agents produced by endophytic fungi of cool-season grasses. These alkaloids are composed of a pyrrolizidine ring system and an uncommon ether bridge linking carbons 2 and 7. Previous results indicated that 1-aminopyrrolizidine was a pathway intermediate. We used RNA interference to knock down expression of lolO, resulting in the accumulation of an alkaloid identified as exo-1-acetamidopyrrolizidine based on high-resolution MS and NMR. Genomes of endophytes differing in alkaloid profiles were sequenced, revealing that those with mutated lolO accumulated exo-1-acetamidopyrrolizidine but no lolines. Heterologous expression of wild-type lolO complemented a lolO mutant, resulting in the production of N-acetylnorloline. These results indicated that the non-heme iron oxygenase, LolO, is required for ether bridge formation, probably through oxidation of exo-1-acetamidopyrrolizidine

    Towards Extractions of the CKM Angle γ\gamma from Bu,d→πKB_{u,d}\to\pi K and Untagged Bs→KKˉB_s\to K\bar{K} Decays

    Full text link
    The decays Bd→π∓K±B_d\to\pi^\mp K^\pm and B±→π±KB^\pm\to\pi^\pm K provide interesting constraints on the angle γ\gamma of the unitarity triangle of the CKM matrix. It is shown that bounds on γ\gamma can also be obtained from the time evolution of untagged Bs→K+K−B_s\to K^+K^- and Bs→K0K0ˉB_s\to K^0\bar{K^0} decays, provided the BsB_s system exhibits a sizeable width difference ΔΓs\Delta\Gamma_s. A detailed discussion of rescattering processes and electroweak penguin effects, which limit the theoretical accuracy of these constraints, and of methods to control them through experimental data is given. Moreover, strategies are pointed out to go beyond these bounds by relating the Bu,d→πKB_{u,d}\to\pi K and untagged Bs→KKˉB_s\to K\bar{K} decays through the SU(3) flavour symmetry of strong interactions. If a tagged, time-dependent measurement of the Bs→K+K−B_s\to K^+K^- and Bs→K0K0ˉB_s\to K^0\bar{K^0} modes should become possible, γ\gamma could be determined from the corresponding observables in a way that makes use of only the SU(2) isospin symmetry and takes into account rescattering effects ``automatically''. The impact of new-physics contributions to Bs0−Bs0ˉB^0_s - \bar{B^0_s} mixing is also analysed, and interesting features arising in such a scenario of physics beyond the Standard Model are pointed out.Comment: 34 pages, LaTeX, 12 figures, extended version including a detailed discussion of rescattering and electroweak penguin effect
    • …
    corecore