Regulation and Identity of Florigen: Flowering Locus T Moves Center Stage

The transition from vegetative to reproductive growth is controlled by day length in many plant species. Day length is perceived in leaves and induces a systemic signal, called florigen, that moves through the phloem to the shoot apex. At the shoot apical meristem (SAM), florigen causes changes in gene expression that reprogram the SAM to form flowers instead of leaves. Analysis of flowering of Arabidopsis thaliana placed the CONSTANS/FLOWERING LOCUS T (CO/FT) module at the core of a pathway that promotes flowering in response to changes in day length. We describe progress in defining the molecular mechanisms that activate this module in response to changing day length and the increasing evidence that FT protein is a major component of florigen. Finally, we discuss conservation of FT function in other species and how variation in its regulation could generate different flowering behaviors

Probing the internal solar magnetic field through g-modes

The observation of g-mode candidates by the SoHO mission opens the possibility of probing the internal structure of the solar radiative zone (RZ) and the solar core more directly than possible via the use of the p-mode helioseismology data. We study the effect of rotation and RZ magnetic fields on g-mode frequencies. Using a self-consistent static MHD magnetic field model we show that a 1% g-mode frequency shift with respect to the Solar Seismic Model (SSeM) prediction, currently hinted in the GOLF data, can be obtained for magnetic fields as low as 300 kG, for current measured modes of radial order n=-20. On the other hand, we also argue that a similar shift for the case of the low order g-mode candidate (l=2, n=-3) frequencies can not result from rotation effects nor from central magnetic fields, unless these exceed 8 MG.Comment: 6 pages, 2 figures; final version to appear in MNRA

Impact of the physical processes in the modeling of HD49933

Context : On its asteroseismic side, the initial run of CoRoT was partly devoted to the solar like star HD49933.The eigenmodes of this F dwarf have been observed with unprecedented accuracy. Aims : We investigate quantitatively the impact of changes in the modeling parameters like mass and composition. More importantly we investigate how a sophisticated physics affects the seismological picture of HD49933. We consider the effects of diffusion, rotation and the changes in convection efficiency. Methods : We use the CESAM stellar evolution code coupled to the ADIPLS adiabatic pulsation package to build secular models and their associated oscillation frequencies. We also exploited the hydrodynamical code STAGGER to perform surface convection calculations. The seismic variables used in this work are : the large frequency separation, the derivative of the surface phase shift,and the eigenfrequencies $\rm \nu_{\ell=0,n=14}$ and $\rm \nu_{\ell=0,n=27}$. Results : Mass and uncertainties on the composition have much larger impacts on the seismic variables we consider than the rotation. The derivative of the surface phase shift is a promising variable for the determination of the helium content. The seismological variables of HD49933 are sensitive to the assumed solar composition and also to the presence of diffusion in the models.Comment: 7 pages, 3 figures, 7 table

Information integration and decision making in flowering time control

In order to successfully reproduce, plants must sense changes in their environment and flower at the correct time. Many plants utilize day length and vernalization, a mechanism for verifying that winter has occurred, to determine when to flower. Our study used available temperature and day length data from different climates to provide a general understanding how this information processing of environmental signals could have evolved in plants. For climates where temperature fluctuation correlations decayed exponentially, a simple stochastic model characterizing vernalization was able to reconstruct the switch-like behavior of the core flowering regulatory genes. For these and other climates, artificial neural networks were used to predict flowering gene expression patterns. For temperate plants, long-term cold temperature and short-term day length measurements were sufficient to produce robust flowering time decisions from the neural networks. Additionally, evolutionary simulations on neural networks confirmed that the combined signal of temperature and day length achieved the highest fitness relative to neural networks with access to only one of those inputs. We suggest that winter temperature memory is a well-adapted strategy for plants' detection of seasonal changes, and absolute day length is useful for the subsequent triggering of flowering

The Arabidopsis Polycomb Repressive Complex 1 (PRC1) components AtBMI1A, B and C impact gene networks throughout all stages of plant development.

Polycomb Group regulation in Arabidopsis (Arabidopsis thaliana) is required to maintain cell differentiation and allow developmental phase transitions. This is achieved by the activity of three PcG repressive complex 2s (PRC2s) and the participation of a yet poorly defined PRC1. Previous results showed that apparent PRC1 components perform discrete roles during plant development, suggesting the existence of PRC1 variants; however, it is not clear in how many processes these components participate. We show that AtBMI1 proteins are required to promote all developmental phase transitions and to control cell proliferation during organ growth and development, expanding their proposed range of action. While AtBMI1 function during germination is closely linked to B3 domain transcription factors VAL1/2 possibly in combination with GT-box binding factors, other AtBMI1 regulatory networks require participation of different factor combinations. Conversely, EMF1 and LHP1 bind many H3K27me3 positive genes up-regulated in atbmi1a/b/c mutants; however, loss of their function affects expression of a different subset, suggesting that even if EMF1, LHP1, and AtBMI1 exist in a common PRC1 variant, their role in repression depends on the functional context

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

Seismology of stars is strongly developing. To address this question we have formed an international collaboration OPAC to perform specific experimental measurements, compare opacity calculations and improve the opacity calculations in the stellar codes [1]. We consider the following opacity codes: SCO, CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large differences for Fe and Ni in equivalent conditions of envelopes of type II supernova precursors, temperatures between 15 and 40 eV and densities of a few mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar results and differ from OP ones for the lower temperatures and for spectral interval values [3]. In this work we discuss the role of Configuration Interaction (CI) and the influence of the number of used configurations. We present and include in the opacity code comparisons new HULLAC-v9 calculations [5, 6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data. Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences 201