LED Color Gradient As A New Screening Tool For Rapid Phenotyping Of Plant Responses To Light Quality

Background The increasing demand for local food production is fueling high interest in the development of controlled environment agriculture. In particular, LED technology brings energy-saving advantages together with the possibility to manipulate plant phenotypes through light quality control. However, optimizing light quality is required for each cultivated plant and specific purpose. Findings In this paper, it is shown that the combination of LED gradient setups with imaging-based non-destructive plant phenotyping constitutes an interesting new screening tool with the potential to improve speed, logistics, and information output. To validate this concept, an experiment was performed to evaluate the effects of a complete range of Red:Blue ratios on seven plant species: Arabidopsis thaliana, Brachypodium distachyon, Euphorbia peplus, Ocimum basilicum, Oryza sativa, Solanum lycopersicum, and Setaria viridis. Plants were exposed during 30 days to the light gradient and showed significant, but species-dependent, responses in terms of dimension, shape, and color. A time series analysis of phenotypic descriptors highlighted growth changes but also transient responses of plant shapes to the Red:Blue ratio. Conclusion This approach, which generated a large reusable dataset, can be adapted for addressing specific needs in crop production or fundamental questions in photobiology.VeLire, Tropical Plant Factory (Plant'HP

Exploring the mechanisms of photoperiod sensing in Brachypodium distachyon

In crops, the proper timing of flowering, which relies on the coordination of exogenous cues with an endogenous developmental program, is crucial to maximize yields. In Brachypodium distachyon, a model temperate grass, the perception of the increasing day lengths of the spring is key to promote the induction of flowering through a complex interplay between the photoperiodic pathway and circadian clock-controlled processes. Here, we summarize the current knowledge of the flowering time control in B. distachyon and describe a mutant allele of the EARLY FLOWERING 3 (ELF3) gene, which was identified through a forward genetic screening for early flowering phenotypes under short day photoperiods. The mutation of elf3 accelerates flowering under most tested photoperiods. This mutant remained sensitive to vernalization but not to changes in the ambient temperature. The early flowering phenotype is corroborated, at the molecular level, with an increase in the expression of genes promoting flowering, the deregulation of the circadian clock rhythms, and the suppression of the expression of the short-day marker FTL9. Finally, to explore the mechanisms through which the photoperiodic pathway regulates flowering, we tested the effect of night breaks and light quality on the induction of flowering in B. distachyon

Hydrodynamics of high-redshift galaxy collisions: From gas-rich disks to dispersion-dominated mergers and compact spheroids

Disk galaxies at high redshift (z~2) are characterized by high fractions of cold gas, strong turbulence, and giant star-forming clumps. Major mergers of disk galaxies at high redshift should then generally involve such turbulent clumpy disks. Merger simulations, however, model the ISM as a stable, homogeneous, and thermally pressurized medium. We present the first merger simulations with high fractions of cold, turbulent, and clumpy gas. We discuss the major new features of these models compared to models where the gas is artificially stabilized and warmed. Gas turbulence, which is already strong in high-redshift disks, is further enhanced in mergers. Some phases are dispersion-dominated, with most of the gas kinetic energy in the form of velocity dispersion and very chaotic velocity fields, unlike merger models using a thermally stabilized gas. These mergers can reach very high star formation rates, and have multi-component gas spectra consistent with SubMillimeter Galaxies. Major mergers with high fractions of cold turbulent gas are also characterized by highly dissipative gas collapse to the center of mass, with the stellar component following in a global contraction. The final galaxies are early-type with relatively small radii and high Sersic indices, like high-redshift compact spheroids. The mass fraction in a disk component that survives or re-forms after a merger is severely reduced compared to models with stabilized gas, and the formation of a massive disk component would require significant accretion of external baryons afterwards. Mergers thus appear to destroy extended disks even when the gas fraction is high, and this lends further support to smooth infall as the main formation mechanism for massive disk galaxies.Comment: ApJ accepte

An Observed Link between Active Galactic Nuclei and Violent Disk Instabilities in High-Redshift Galaxies

We provide evidence for a correlation between the presence of giant clumps and the occurrence of active galactic nuclei (AGN) in disk galaxies. Giant clumps of 10^8-9 Msun arise from violent gravitational instability in gas-rich galaxies, and it has been proposed that this instability could feed supermassive black holes (BH). We use emission line diagnostics to compare a sample of 14 clumpy (unstable) disks and a sample of 13 smoother (stable) disks at redshift z~0.7. The majority of clumpy disks in our sample have a high probability of containing AGN. Their [OIII] emission line is strongly excited, inconsistent with low-metallicity star formation alone. [NeIII] excitation is also higher. Stable disks rarely have such properties. Stacking ultra sensitive Chandra observations (4 Ms) reveals an X-ray excess in clumpy galaxies, which cannot be solely due to star formation and confirms the presence of AGN. The clumpy galaxies in our intermediate-redshift sample have properties typical of gas-rich disk galaxies rather than mergers, being in particular on the Main Sequence of star formation. This suggests that our findings apply to the physically-similar and numerous gas-rich unstable disks at z>1. Using the observed [OIII] and X-ray luminosities, we conservatively estimate that AGN hosted by clumpy disks have typical bolometric luminosities of the order of a few 10^43 erg/s, BH growth rates ~10^-2 Msun/yr, and that these AGN are substantially obscured in X-rays. This moderate-luminosity mode could be sufficient to provide a large fraction of today's BH mass over a couple of Gyr given that our observations suggest a high duty cycle (>10%), accretion bursts with higher luminosities being possible over shorter phases. The observed evolution of disk instabilities with mass and redshift could explain the simultaneous downsizing of star formation and of BH growth.Comment: ApJ in pres

Integrating roots into a whole-plant map of flowering-time gene networks in Arabidopsis thaliana

Flowering is a crucial step in plant development that needs to be carefully regulated to occur at the right time of the year, thus ensuring reproductive success. In Arabidopsis thaliana, several interconnected molecular networks have been disclosed that mediate flowering response to environmental cues, such as photoperiod and temperature, or to endogenous factors, such as plant age or hormones. Many of these signalling pathways are systemic, i.e. involve regulatory mechanisms distant from the shoot apical meristem where floral transition eventually occurs. However, most investigations were focused on the aerial parts of the plant but ignored the roots. The aim of this Ph.D. thesis was to integrate the roots into a comprehensive overview of the genetic control of flowering in Arabidopsis. A prerequisite was to obtain a full list of known flowering-time genes. This step led to the creation of a database of flowering-time genes, which is accessible online and in which users can navigate through data tables or interactive schemes (www.flor-id.org). In the second part of the work, we studied the involvement of the roots in the differential developmental rates of plants grown in hydroponics and on soil. In the third part of the work, we used data mining analyses to show that about 200 flowering-time genes are expressed in the roots of Arabidopsis. Using a complementary approach, we analysed the root transcriptome to identify early changes occurring during the induction of flowering by a photoperiodic treatment. Collectively, the results presented in this work brought new insights in the regulation of flowering time at the whole-organism scale by integrating the “hidden part” of plants in the current landscape of the molecular processes controlling phase transitions in Arabidopsis thaliana

Heat can erase epigenetic marks of vernalization in Arabidopsis

Vernalization establishes a memory of winter that must be maintained for weeks or months in order to promote flowering the following spring. The stability of the vernalized state varies among plant species and depends on the duration of cold exposure. In Arabidopsis thaliana, winter leads to epigenetic silencing of the floral repressor gene FLOWERING LOCUS C (FLC) and the duration of cold is measured through the dynamics of chromatin modifications during and after cold. The growing conditions encountered post-vernalization are thus critical for the maintenance of the vernalized state. We reported that high temperature leads to devernalization and, consistently, to FLC reactivation in Arabidopsis seedlings. Here we show that the repressive epigenetic mark H3K27me3 decreases at the FLC locus when vernalized seedlings are grown at 30°C, unless they were first exposed to a stabilizing period at 20°C. Ambient temperature thus controls the epigenetic memory of winter

Communicating Effectively with Scientific Infographics

<a>Publishing scientific articles requires a lot of patience, as the overall process takes months to years. </a>When your research is finally published, you want it to be noticed by the scientific community. One way to achieve this goal is to create graphical abstracts that you and your co-authors will use to advertise your research. In this seminar, I describe the <b>resources</b>, the <b>tools</b>, and the <b>workflow</b> that I use to create these infographics. The goal of this presentation is to set you on the path to create graphical abstracts to advertise your own research work

Arabidopsis phyllotaxy

<b>Arabidopsis phyllotaxy.</b><div><br></div><div>This illustration is available under a CC-BY license: it can be used and modified with appropriate credits. <br></div

microRNAs in Arabidopsis : discovery, functions and roles in the control of flowering time

<p>Discovered about 20 years ago, microRNA are small non-coding RNA (21-23 nt) involved in the post-transcriptional regulation of gene expression. They are involved in numerous regulatory pathways. However, the analysis of their function and their expression level is a bit tricky, explaining that they were only integrated in the molecular pathways during the last decade.</p> <p>Here, we present a brief summary of the events that lead to the discovery of microRNAs, as well as the molecular tools used for their analysis and their role in the molecular control of flowering time.</p> <p>Of course, feel free to leave any constructive comment about those slides !</p

Unraveling the molecular mechanisms controlling flowering in the model temperate grass Brachypodium distachyon

Slides presented at the annual ASPB meeting Plant Biology 2017, in Honolulu (HI)