Experimental evolution induces loss of female-fertility in vitro in the fungal pathogen of rice, Magnaporthe oryzae

Sexual reproduction is widespread in eukaryotic organisms. Inmany fungal species previously known to reproduce asexually, some populations have been shown to encounter episodes of sexual reproduction. It has been suggested that mostfungi that are pathogenic on plants may reproduce sexually near their center of origin but have lost this ability during their dispersion. If a population reproduces exclusively clonally forseveral generations, individuals may accumulate deleterious mutations in loci controlling sexual reproduction. This may result in a complete loss of sexual reproduction ability. We tested this hypothesis on /Magnaporthe oryzae/, which is responsible for the most important fungal disease on cultivated rice worldwide: blast. In this species, only asexual spores are observed in the field. However, some strains coming from the putative center of origin of the fungus (in South East Asia, near the Himalayan Foothills) are able to produce viable sexual spores /in vitro/, and indirect evidence that sexual reproduction do occur /in natura/ in this region have been recently provided (see the abstract by E. Fournier).//In this heterothallic fungus,//sexual reproduction can occur only between two different strains of opposite mating type. Moreover, at least one of them, independently from the mating type, must be female-fertile, that is to be able to produce the sexual organs (perithecia) where meiosis takes place. We performed /in vitro /experimental evolution of four female-fertile strains for 10-20 "clonal generations". These strains came from a recombinant population of the center of origin. Each of the four strains became female-sterile in about 100 days in at least one of the two replicates we performed. This loss of female-fertility was accompanied by a reduction of asexual sporulation /in vitro /and /in planta/.//As epigenetical effects could explain the frequent loss of female-fertility observed, we tested if stress could restore it. Four different stresses were tested: extremely low temperature (-80°C), mycelium fragmentation by sonication, monosporic isolation, growth on plant. None of these stresses achieved to restore female-fertility, so the loss of female-fertility might be explained by genetical rather than epigenetical mechanisms. Crosses were performed between mutant strains that had lost female-fertility and wild type strains. In the offspring, the female-fertility phenotype segregated in 1:3 proportions. Backcrosses between F1 female-sterile strains and wild type strains gave the same result, supporting the hypothesis of a genetic control. Here we showed for the first time that female-fertility could be rapidly lost in theabsence of sexual reproduction in /M. oryzae/ strains from rice. We showed that it might be due to mutation accumulation, probably at several loci. From these results we hypothesize that sexual reproduction ability may have been lost rapidly during the dispersion of the disease from Asia to the rest of the world. More generally, this study provides a case study to test hypotheses on the enigma of sex. (Texte intégral

Delayed Babcock-Leighton dynamos in the diffusion-dominated regime

Context. Solar dynamo models of Babcock-Leighton type typically assume the rise of magnetic flux tubes to be instantaneous. Solutions with high-magnetic-diffusivity have too short periods and a wrong migration of their active belts. Only the low-diffusivity regime with advective meridional flows is usually considered. Aims. In the present paper we discuss these assumptions and applied a time delay in the source term of the azimuthally averaged induction equation. This delay is set to be the rise time of magnetic flux tubes which supposedly form at the tachocline. We study the effect of the delay, which adds to the spacial non-locality a non-linear temporal one, in the advective but particularly in the diffusive regime. Methods. Fournier et al. (2017) obtained the rise time according to stellar parameters such as rotation, and the magnetic field strength at the bottom of the convection zone. These results allowed us to constrain the delay in the mean-field model used in a parameter study. Results. We identify an unknown family of solutions. These solutions self-quench, and exhibit longer periods than their non-delayed counterparts. Additionally, we demonstrate that the non-linear delay is responsible for the recover of the equatorward migration of the active belts at high turbulent diffusivities. Conclusions. By introducing a non-linear temporal non-locality (the delay) in a Babcock-Leighton dynamo model, we could obtain solutions quantitatively comparable to the solar butterfly diagram in the diffusion-dominated regime.Comment: 11 pages, 10 Figure

Pinsker estimators for local helioseismology

A major goal of helioseismology is the three-dimensional reconstruction of the three velocity components of convective flows in the solar interior from sets of wave travel-time measurements. For small amplitude flows, the forward problem is described in good approximation by a large system of convolution equations. The input observations are highly noisy random vectors with a known dense covariance matrix. This leads to a large statistical linear inverse problem. Whereas for deterministic linear inverse problems several computationally efficient minimax optimal regularization methods exist, only one minimax-optimal linear estimator exists for statistical linear inverse problems: the Pinsker estimator. However, it is often computationally inefficient because it requires a singular value decomposition of the forward operator or it is not applicable because of an unknown noise covariance matrix, so it is rarely used for real-world problems. These limitations do not apply in helioseismology. We present a simplified proof of the optimality properties of the Pinsker estimator and show that it yields significantly better reconstructions than traditional inversion methods used in helioseismology, i.e.\ Regularized Least Squares (Tikhonov regularization) and SOLA (approximate inverse) methods. Moreover, we discuss the incorporation of the mass conservation constraint in the Pinsker scheme using staggered grids. With this improvement we can reconstruct not only horizontal, but also vertical velocity components that are much smaller in amplitude

Field-dependent diamagnetic transition in magnetic superconductor Sm1.85Ce0.15CuO4−ySm_{1.85} Ce_{0.15} Cu O_{4-y}

The magnetic penetration depth of single crystal $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ was measured down to 0.4 K in dc fields up to 7 kOe. For insulating $\rm{Sm_2CuO_4}$, Sm$^{3+}$ spins order at the N\'{e}el temperature, $T_N = 6$ K, independent of the applied field. Superconducting $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ ($T_c \approx 23$ K) shows a sharp increase in diamagnetic screening below $T^{\ast}(H)$ which varied from 4.0 K ($H = 0$) to 0.5 K ($H =$ 7 kOe) for a field along the c-axis. If the field was aligned parallel to the conducting planes, $T^{\ast}$ remained unchanged. The unusual field dependence of $T^{\ast}$ indicates a spin freezing transition that dramatically increases the superfluid density.Comment: 4 pages, RevTex

Discrimination of the light CP-odd scalars between in the NMSSM and in the SLHM

The presence of the light CP-odd scalar boson predicted in the next-to-minimal supersymmetric model (NMSSM) and the simplest little Higgs model (SLHM) dramatically changes the phenomenology of the Higgs sector. We suggest a practical strategy to discriminate the underlying model of the CP-odd scalar boson produced in the decay of the standard model-like Higgs boson. We define the decay rate of "the non $b$-tagged jet pair" with which we compute the ratio of decay rates into lepton and jets. They show much different behaviors between the NMSSM and the SLHM.Comment: 5 pages, 2 figures (5 figure files

Density Power Spectrum of Compressible Hydrodynamic Turbulent Flows

Turbulent flows are ubiquitous in astrophysical environments, and understanding density structures and their statistics in turbulent media is of great importance in astrophysics. In this paper, we study the density power spectra, $P_{\rho}$, of transonic and supersonic turbulent flows through one and three-dimensional simulations of driven, isothermal hydrodynamic turbulence with root-mean-square Mach number in the range of 1 \la M_{\rm rms} \la 10. From one-dimensional experiments we find that the slope of the density power spectra becomes gradually shallower as the rms Mach number increases. It is because the density distribution transforms from the profile with {\it discontinuities} having $P_{\rho} \propto k^{-2}$ for $M_{\rm rms} \sim 1$ to the profile with {\it peaks} having $P_{\rho} \propto k^0$ for $M_{\rm rms} \gg 1$. We also find that the same trend is carried to three-dimension; that is, the density power spectrum flattens as the Mach number increases. But the density power spectrum of the flow with $M_{\rm rms} \sim 1$ has the Kolmogorov slope. The flattening is the consequence of the dominant density structures of {\it filaments} and {\it sheets}. Observations have claimed different slopes of density power spectra for electron density and cold H I gas in the interstellar medium. We argue that while the Kolmogorov spectrum for electron density reflects the {\it transonic} turbulence of $M_{\rm rms} \sim 1$ in the warm ionized medium, the shallower spectrum of cold H I gas reflects the {\it supersonic} turbulence of $M_{\rm rms} \sim$ a few in the cold neutral medium.Comment: To appear in ApJ Lett. Pdf file with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/kimryu.pd

FINANCING LOCAL DEVELOPMENT

Community/Rural/Urban Development,

Universal analytic properties of noise. Introducing the J-Matrix formalism

We propose a new method in the spectral analysis of noisy time-series data for damped oscillators. From the Jacobi three terms recursive relation for the denominators of the Pad\'e Approximations built on the well-known Z-transform of an infinite time-series, we build an Hilbert space operator, a J-Operator, where each bound state (inside the unit circle in the complex plane) is simply associated to one damped oscillator while the continuous spectrum of the J-Operator, which lies on the unit circle itself, is shown to represent the noise. Signal and noise are thus clearly separated in the complex plane. For a finite time series of length 2N, the J-operator is replaced by a finite order J-Matrix J_N, having N eigenvalues which are time reversal covariant. Different classes of input noise, such as blank (white and uniform), Gaussian and pink, are discussed in detail, the J-Matrix formalism allowing us to efficiently calculate hundreds of poles of the Z-transform. Evidence of a universal behaviour in the final statistical distribution of the associated poles and zeros of the Z-transform is shown. In particular the poles and zeros tend, when the length of the time series goes to infinity, to a uniform angular distribution on the unit circle. Therefore at finite order, the roots of unity in the complex plane appear to be noise attractors. We show that the Z-transform presents the exceptional feature of allowing lossless undersampling and how to make use of this property. A few basic examples are given to suggest the power of the proposed method.Comment: 14 pages, 8 figure