Turning Meiosis into Mitosis

The mutation of as few as three genes in a sexual plant transforms meiosis into mitosis and results in diploid gametes that are genetically identical to the mother plant. This phenotype resembles apomeiosis, which is a major step in apomixis

Mutations in AtPS1 (Arabidopsis thaliana Parallel Spindle 1) Lead to the Production of Diploid Pollen Grains

Polyploidy has had a considerable impact on the evolution of many eukaryotes, especially angiosperms. Indeed, most—if not all—angiosperms have experienced at least one round of polyploidy during the course of their evolution, and many important crop plants are current polyploids. The occurrence of 2n gametes (diplogametes) in diploid populations is widely recognised as the major source of polyploid formation. However, limited information is available on the genetic control of diplogamete production. Here, we describe the isolation and characterisation of the first gene, AtPS1 (Arabidopsis thaliana Parallel Spindle 1), implicated in the formation of a high frequency of diplogametes in plants. Atps1 mutants produce diploid male spores, diploid pollen grains, and spontaneous triploid plants in the next generation. Female meiosis is not affected in the mutant. We demonstrated that abnormal spindle orientation at male meiosis II leads to diplogamete formation. Most of the parent's heterozygosity is therefore conserved in the Atps1 diploid gametes, which is a key issue for plant breeding. The AtPS1 protein is conserved throughout the plant kingdom and carries domains suggestive of a regulatory function. The isolation of a gene involved in diplogamete production opens the way for new strategies in plant breeding programmes and progress in evolutionary studies

Stable isotope characterization of pedogenic and lacustrine carbonates from the Chinese Tian Shan: constraints on the Mesozoic - Lower Cenozoic palaeo-environmental evolution

International audienceIn the Mesozoic–Cenozoic continental deposits of the Tian Shan area, two main levels containing pedogenic carbonates have been identified on both the southern and northern foothills of the range: one in the Upper Jurassic series and one in the Upper Cretaceous–Lower Palaeocene series. In order to reconstruct the palaeoenvironmental and palaeotopographic characteristics of the Tian Shan area during these two periods, we measured the oxygen and carbon isotope composition of these pedogenic carbonates (calcrete and nodules). The stable isotope compositions are homogeneous: most δ18O values are between 21 and 25‰ and most δ13C values are between −4 and −6‰. No distinction can be made between the calcrete and nodule isotopic compositions. The constancy of isotopic values across the Tian Shan is evidence of a development of these calcification features in similar palaeoenvironmental conditions. The main inference is that no significant relief existed in that area at the Cretaceous−Palaeogene boundary, implying that most of the present relief developed later, during the Cenozoic. In addition to the pedogenic carbonates, few beds of limestones interstratified in the Jurassic series of the southern foothills display oxygen and carbon isotope compositions typical of lacustrine carbonates, ruling out brackish water incursion at that period in the regio

Les documents scientifiques informels: un patrimoine peu exploré, témoin de la construction des savoirs

L'objectif du projet ECRITO était de contribuer à préserver et à valoriser les documents scientifiques produits quotidiennement par les chercheurs de Midi-Pyrénées, en amont des publications formelles : non seulement les articles, communications ou monographies, qui constituent la partie visible de la recherche, mais aussi tous les matériaux et informations accumulés par les chercheurs, et sur la base desquels se construit leur travail. Ces matériaux sont de types très divers : littérature " grise " (rapports, mémoires, documentation techniques...), documents textuels " informels " (carnets, notes, brouillons, correspondances, cahiers de laboratoires), corpus visuels, sonores ou multimédia (campagnes photographiques, campagnes d'enquêtes, enregistrements audio ou vidéo), données électroniques (bases de données, fichiers informatiques), etc. Le projet visait également à prolonger, de manière exploratoire, le questionnement sur le patrimoine scientifique à partir des traces matérielles produites quotidiennement par les chercheurs dans leurs activités de recherche. Ces traces représentent en effet une fenêtre irremplaçable sur la science en train de se construire : elles permettent de rendre visible et compréhensible le processus habituellement dissimulé de production de la science, ce qui constitue un enjeu scientifique et pédagogique fondamental

The CYCLIN-A CYCA1;2/TAM Is Required for the Meiosis I to Meiosis II Transition and Cooperates with OSD1 for the Prophase to First Meiotic Division Transition

Meiosis halves the chromosome number because its two divisions follow a single round of DNA replication. This process involves two cell transitions, the transition from prophase to the first meiotic division (meiosis I) and the unique meiosis I to meiosis II transition. We show here that the A-type cyclin CYCA1;2/TAM plays a major role in both transitions in Arabidopsis. A series of tam mutants failed to enter meiosis II and thus produced diploid spores and functional diploid gametes. These diploid gametes had a recombined genotype produced through the single meiosis I division. In addition, by combining the tam-2 mutation with AtSpo11-1 and Atrec8, we obtained plants producing diploid gametes through a mitotic-like division that were genetically identical to their parents. Thus tam alleles displayed phenotypes very similar to that of the previously described osd1 mutant. Combining tam and osd1 mutations leads to a failure in the prophase to meiosis I transition during male meiosis and to the production of tetraploid spores and gametes. This suggests that TAM and OSD1 are involved in the control of both meiotic transitions

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

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Influence de la teneur en glucides solubles des feuilles de Zea mays L. sur le choix du site de ponte de la pyrale, Ostrinia nubilalis Hbn. (Lepid. Pyralidae)

Le choix du site de ponte par Ostrinia nubilalis (Hbn.) varie avec l’hybride de maïs. Une tentative d’explication biochimique de ce choix est entreprise sur l’hybride le plus favorable à la ponte. Elle consiste, par passage prolongé de la plante à l’obscurité, à faire varier la teneur en glucides solubles des feuilles et à examiner les répercussions sur le comportement de l’insecte. Les femelles de pyrale pondent beaucoup moins sur les plantes appauvries et la répartition des ooplaques sur la plante est également modifiée. Une corrélation est établie entre le nombre d’ooplaques déposées sur la plante, la teneur en saccharose et, à un moindre degré, la teneur en glucose de ses feuilles.Egg laying by Ostrinia nubilalis (Hbn.) varies with the maize hybrid used. An attempt was made to provide a biochemical explanation of egg-laying site choice, using the most favourable hybrid for egg laying. Our approach consisted in modifying the soluble sugar content of leaves by prolonged dark exposure of plants and examining its effect on insect behaviour. European corn borer females laid fewer eggs on plants less rich in sugars ; the distribution of egg masses on the plant was also modified. A correlation was established between the number of egg masses deposited on the plant and the sucrose (or to a lesser extent glucose) content of its leaves