Strigolactone biosynthesis and signaling in plant development.

Strigolactones (SLs), first identified for their role in parasitic and symbiotic interactions in the rhizosphere, constitute the most recently discovered group of plant hormones. They are best known for their role in shoot branching but, more recently, roles for SLs in other aspects of plant development have emerged. In the last five years, insights into the SL biosynthetic pathway have also been revealed and several key components of the SL signaling pathway have been identified. Here, and in the accompanying poster, we summarize our current understanding of the SL pathway and discuss how this pathway regulates plant development

The pea branching RMS2 gene encodes the PsAFB4/5 auxin receptor and is involved in an auxin-strigolactone regulation loop

Strigolactones (SLs) are well known for their role in repressing shoot branching. In pea, increased transcript levels of SL biosynthesis genes are observed in stems of highly branched SL deficient (ramosus1 (rms1) and rms5) and SL response (rms3 and rms4) mutants indicative of negative feedback control. In contrast, the highly branched rms2 mutant has reduced transcript levels of SL biosynthesis genes. Grafting studies and hormone quantification led to a model where RMS2 mediates a shoot-to-root feedback signal that regulates both SL biosynthesis gene transcript levels and xylem sap levels of cytokinin exported from roots. Here we cloned RMS2 using synteny with Medicago truncatula and demonstrated that it encodes a putative auxin receptor of the AFB4/5 clade. Phenotypes similar to rms2 were found in Arabidopsis afb4/5 mutants, including increased shoot branching, low expression of SL biosynthesis genes and high auxin levels in stems. Moreover, afb4/5 and rms2 display a specific resistance to the herbicide picloram. Yeast-two-hybrid experiments supported the hypothesis that the RMS2 protein functions as an auxin receptor. SL root feeding using hydroponics repressed auxin levels in stems and down-regulated transcript levels of auxin biosynthesis genes within one hour. This auxin down-regulation was also observed in plants treated with the polar auxin transport inhibitor NPA. Together these data suggest a homeostatic feedback loop in which auxin up-regulates SL synthesis in an RMS2-dependent manner and SL down-regulates auxin synthesis in an RMS3 and RMS4- dependent manner

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Strigolactones, a novel class of plant hormone controlling shoot branching

For several decades, auxin and cytokinin were the only two hormones known to be involved in the control of shoot branching through apical dominance, a process where the shoot apex producing auxin inhibits the outgrowth of axillary buds located below. Grafting studies with high branching mutants and cloning of the mutated genes demonstrated the existence of a novel long distance carotenoid derived signal which acted as a branching inhibitor. Recently, this branching inhibitor has been shown to belong to the strigolactones, a group of small molecules already known to be produced by roots, exuded in the rhizosphere and as having a role in both parasitic and symbiotic interactions.Depuis les années 1930, l’auxine et les cytokinines étaient les deux seules hormones connues pour être impliquées dans le contrôle de la ramification des plantes par le processus de la dominance apicale par lequel l’apex de la tige, producteur d’auxine, inhibe le démarrage des bourgeons axillaires sous-jacents. Des expériences de greffes avec des mutants hyper-ramifiés et le clonage des gènes mutés ont permis de démontrer l’existence d’un nouveau signal dérivé de caroténoides agissant à longue distance et réprimant la ramification. Récemment, il a été démontré que cet inhibiteur de la ramification fait partie des strigolactones, groupe de petites molécules déjà connues pour être produites par les racines des plantes et exsudées dans la rhizosphère où elles jouent un rôle dans des interactions parasitaires et symbiotiques

Interpretation of performances of hybrids obtained from 43 asparagus parent genotypes

The data used were the yields of 231 distinct hybrids grown in long-term multi-site trials (10 yr, 4 sites), resulting from the crossing of 43 genotypes. Genotype-environment interaction was taken into account by means of a factorial regression model previously defined through the varieties used as controls in the trials. Two environmental covariates were used: the latitude of the site, and the type of production (green or white asparagus). It is shown in this paper that most of main effects and genotype-environment interactions could be explained by additive and symmetrical parental influences. The pseudo-diallel structure was therefore reduced to the values of 3 parameters associated with each parent (main effect and 2 regression coefficients) and could thus be easily interpreted. The model was used to evaluate yields of all 816 possible hybrids within chosen environmental conditions.Les rendements de 231 hybrides différents constituent l’ensemble des données utilisé, provenant d’un réseau d’expérimentation comprenant 10 années et 4 lieux. Les interactions génotype-milieu sont prises en compte par le biais d’un modèle de régression factorielle établi dans un travail antérieur à partir des variétés utilisées comme témoin dans le dispositif. Deux covariables du milieu sont utilisées : la latitude du lieu et le type de production (asperge blanche ou verte) dans le lieu et l’année. On arrive à la conclusion que les effets principaux et les interactions génotype-milieu peuvent être décrites par des effets parentaux additifs et symétriques. L’interprétation du pseudo-diallèle peut donc être facilement établie grâce aux valeurs de 3 paramètres (effet principal et 2 coefficients de régression) caractérisant chacun des 43 génotypes parentaux. Enfin la valeur hypothétique des hybrides est prédite (y compris pour les hybrides non expérimentés) grâce au modèle retenu pour des conditions d’un milieu déterminé

Characterization of environments in long-term multi-site trials in Asparagus, through yield of standard varieties and use of environmental covariates

International audienc

Flowering time in pea (a systems biology approach from the genetic network to the field)

Le pois, à la fois espèce modèle pour l étude du développement et espèce agronomique, représente un sujet idéal pour des études intégrées à différentes échelles. La transition florale est un caractère clé du développement et des approches variées ont conduit à différents modèles. Les approches de génétique et physiologie menées en conditions contrôlées sur une large gamme de mutants ont conduit au développement d un modèle descriptif pour les interactions entre les gènes connus contrôlant la floraison. Les études en plein champ ont permis de développer des modèles écophysiologiques de la date de floraison en fonction de la photopériode et de la température qui ne prennent pas en compte le génotype. Plus récemment, les données sur Arabidopsis thaliana permettent d avoir une compréhension au niveau moléculaire des mécanismes en jeu. Ce projet est une première approche pour intégrer ce large jeu de données au sein d un modèle prédictif de la date d initiation florale, décomposé sous la forme du produit mathématique du premier nœud d initiation florale (NFI) et du temps nécessaire à l initiation d un nouveau nœud à l apex (plastochrone). Un premier modèle mathématique pour la régulation génétique du NFI a été développé qui permet de prédire le NFI pour différents génotypes et photopériodes. Les réponses du NFI et du plastochrone aux conditions environnementales ont été analysées précisément. Je me suis intéressée particulièrement aux deux gènes clés de floraison LATE FLOWERING (LF) et HIGH RESPONSE TO PHOTOPERIOD (HR). Ce travail propose des pistes pour exploiter l approche de modélisation pour la floraison chez le pois à la lumière des nouvelles données moléculaires.Pea (Pisum sativum) represents a valuable model species for systems biology approaches, as it is both a crop a model species that has been used for decades to investigate developmental processes. Various approaches led to a tremendous amount of data on flowering : (i) genetic and physiological approaches carried out on non-allelic flowering mutants under controlled conditions allowed the development of a descriptive, non-predictive model for the genetic regulation of flowering in pea; (ii) extensive studies on environmental control of flowering led to agroecophysiological models for flowering time prediction. Additionally, recent molecular advances in pea and the model species Arabidopsis thaliana improved the knowledge on the regulation of flowering. The objective of this work was to integrate this wide range of date into a predictive model in which the time of flower initiation has been broken down into two components variables: the node of first open flower (NFI) and the duration between initiation of two nodes (plastochron). I developed a first predictive model for NFI, based on genetic and photoperiodic control of flowering in pea. Furthermore, analyses of lines grown under field conditions allowed a better understanding of NFI and plastochron responses to environmental conditions. These systems biology approaches were complemented by the molecular study of the two pea flowering key genes LATE FLOWERING (LF) and HIGH RESPONSE TO PHOTOPERIOD (HR). These results, together with the new molecular data, lead to a better understanding of the genetic control of flowering and development in pea. This work opens new avenues to modelling approaches for flowering in pea.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF