Combining biological approaches to highlight the evolution of Musa complex

The diversity of the banana complex can be deciphered only by jointly characterizing the original wild species and their relatives, the primitive diploid forms and the triploid varieties. Sexuality, the primary source of diversity, is strongly disrupted in the cultivated varieties (sterility, parthenocarpy and vegetative propagation) and is relayed by human selection of punctuated mutations vegetatively maintained. Many biological tools illustrate peculiar facets of the diversity and their joint analysis enables an evolutionary reading of this diversity. The access to forms resulting from ancient events and vegetatively maintained is a valuable asset. We propose various assumptions in the structure of wild species, on the domestication of the edible diploids from hybrids between wild forms, on the direct ancestry of triploids from cultivated diploids, and on the ancient migrations. The comparison with data from archaeology, linguistics and human genetics will enable the validation, refinement and dating of the proposed domestication process. (Texte intégral

Histoire évolutive d'intégrations virales infectieuses chez les bananiers M. balbisiana

Des séquences virales des espèces du Banana streak virus-BSV sont présentes de manière illégitime dans le génome des bananiers, l'intégration ne faisant pas partie du cycle de réplication du virus. Les BSV présentent ainsi la caractéristique surprenante de provenir soit de virions soit d'intégrations virales au génome bananier. Bien que ces intégrations proviennent certainement d'évènements accidentels, ils constituent un cas extrême de parasitisme et représentent une stratégie originale de transmission verticale des virus. Dans notre étude nous nous sommes intéressés à retracer l'histoire évolutive de deux intégrations particulières de BSV, celle de l'espèce Golfinger -BSGFV et de l'espèce Imové -BSImV, présentes toutes deux chez le bananier sauvage M. balbisiana cv Pisang Klutuk Wulung et décrites comme à l'origine d'infection. L'accès à la séquence de ces intégrations BSV a permis de définir 13 marqueurs PCR. Ils permettent d'établir des signatures moléculaires spécifiques de l'organisation interne de chacune des intégrations virales ainsi que de leurs zones de jonction au génome Musa. Nous avons ainsi analysé dans un premier temps leur distribution au sein du genre Musa en étudiant leur polymorphisme d'insertion et l'évolution de leur structure. Afin de proposer un scénario évolutif des intégrations BSV nous avons dans un deuxième temps retracé la phylogénie des espèces Musa de notre étude à partir de 2,1 kpb du génome chloroplastique correspondant aux gènes matK et et à la région trnL-trnF ainsi qu'à partir du génome nucléaire en utilisant 19 loci microsatellites. Les premiers résultats indiquent une intégration antérieure à la diversification des M. balbisiana pour les deux espèces virales. Alors que l'intégration BSGFV apparaît conservée pour tous les M. balbisiana, l'intégration BSImV présente une dégradation plus importante avec de nombreuses pertes de séquences. Ces résultats seront présentés et discutés afin de proposer un scénario évolutif de l'interaction tenant compte des possibles conséquences en termes de coût/bénéfices pour le bananier. (Texte intégral

Evaluation of SSR allelic diversity on a broad sample of Musa species with emphasis on robustness of the results obtained

In order to insure further reliable diversity and phylogenetic analysis of Musa complex, the usefulness of 22 simple sequence repeat (SSR) loci is evaluated on a sample of 549 accessions. Robustness of the results was checked by comparing the genotyping results from 4 SSR on the same accessions, in two independent laboratories. We concluded that these markers are suitable for accurate diversity analysis when using appropriate standards, even if some problems linked to PCR amplification still remain with banana accessions leading to less than 10 % of discrepancy. Looking at the allelic diversity of these markers within the 549 accessions, we observed good discrimination between Musa acuminata and Musa balbisiana, the main species in relation to edible bananas, while none at the intra specific level between Musa acuminata subgroups. Analyzing allelic diversity within the main triploids subgroups, we concluded to their likely monoclonal origin. The results also showed some discrepancies between the main groups leading to hypothesis on their evolutionary process. (Résumé d'auteur

Combining Biological Approaches to Shed Light on the Evolution of Edible Bananas

researchDeciphering the diversity of the banana complex needs a joint characterization and analysis of the original wild species and their relatives, primitive diploid forms and triploid derived varieties. Sexuality, the primary source of diversity, is strongly disrupted in the cultivated varieties (sterility, parthenocarpy and vegetative propagation) by human selection of vegetatively maintained punctuated mutations. Many biological tools are available for characterizing this diversity, each one illustrating some peculiar facets, and we show that their joint analysis enables an evolutionary reading of this diversity. We propose various scenarios regarding the structure of wild species, on the domestication of the edible diploids from hybrids between wild forms, on the direct ancestry of triploids from cultivated diploids, and on the ancient migrations dispersing cultivated forms around the world. The comparison with data from archaeology, linguistics and human genetics will enable the validation, refinement and dating of the proposed domestication process

Metabolic characterization of green pods from Vanilla planifolia accessions grown in La Reunion.

Large phenotypic variation has been observed between the cultivated vanillas since a single genetic source of Vanilla planifolia was spread to the Indian Ocean and the Indonesia in the 19th century. In order to differentiate the cultivated vanilla plants, genetic studies have been conducted in the past on the plants grown in various regions such as the French island, La Réunion. However, the genetic difference was not big enough to differentiate diverse accessions of V. planifolia. In this study, metabolomics, in which genetic variation could be amplified, was employed to delve into the variation between the cultivated vanilla plants. To obtain a broad view of the metabolome, nuclear magnetic resonance (NMR) spectroscopy was applied to the analysis of V. planifolia green pods. Principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) of the data showed that the accessions could be differentiated according to their glucovanillin and glucosides A and B contents. Furthermore, a correlation between the glucovanillin content and the pod length, number of flower and growth capacity of the accessions has been observed from the multivariate data analysis

Shoot differentiation from protocorm callus cultures of Vanilla planifolia (Orchidaceae): proteomic and metabolic responses at early stage

<p>Abstract</p> <p>Background</p> <p><it>Vanilla planifolia </it>is an important Orchid commercially cultivated for the production of natural vanilla flavour. Vanilla plants are conventionally propagated by stem cuttings and thus causing injury to the mother plants. Regeneration and <it>in vitro </it>mass multiplication are proposed as an alternative to minimize damage to mother plants. Because mass production of <it>V. planifolia </it>through indirect shoot differentiation from callus culture is rare and may be a successful use of in <it>vitro </it>techniques for producing somaclonal variants, we have established a novel protocol for the regeneration of vanilla plants and investigated the initial biochemical and molecular mechanisms that trigger shoot organogenesis from embryogenic/organogenic callus.</p> <p>Results</p> <p>For embryogenic callus induction, seeds obtained from 7-month-old green pods of <it>V. planifolia </it>were inoculated on MS basal medium (BM) containing TDZ (0.5 mg l^-1). Germination of unorganized mass callus such as protocorm -like structure (PLS) arising from each seed has been observed. The primary embryogenic calli have been formed after transferring on BM containing IAA (0.5 mg l^-1) and TDZ (0.5 mg l^-1). These calli were maintained by subculturing on BM containing IAA (0.5 mg l^-1) and TDZ (0.3 mg l^-1) during 6 months and formed embryogenic/organogenic calli. Histological analysis showed that shoot organogenesis was induced between 15 and 20 days after embryogenic/organogenic calli were transferred onto MS basal medium with NAA (0.5 mg l^-1). By associating proteomics and metabolomics analyses, the biochemical and molecular markers responsible for shoot induction have been studied in 15-day-old calli at the stage where no differentiating part was visible on organogenic calli. Two-dimensional electrophoresis followed by matrix-assisted laser desorption ionization time-of-flight-tandem mass spectrometry (MALDI-TOF-TOF-MS) analysis revealed that 15 protein spots are significantly expressed (<it>P </it>< 0.05) at earlier stages of shoot differentiation. The majority of these proteins are involved in amino acid-protein metabolism and photosynthetic activity. In accordance with proteomic analysis, metabolic profiling using 1D and 2D NMR techniques showed the importance of numerous compounds related with sugar mobilization and nitrogen metabolism. NMR analysis techniques also allowed the identification of some secondary metabolites such as phenolic compounds whose accumulation was enhanced during shoot differentiation.</p> <p>Conclusion</p> <p>The subculture of embryogenic/organogenic calli onto shoot differentiation medium triggers the stimulation of cell metabolism principally at three levels namely (i) initiation of photosynthesis, glycolysis and phenolic compounds synthesis; (ii) amino acid - protein synthesis, and protein stabilization; (iii) sugar degradation. These biochemical mechanisms associated with the initiation of shoot formation during protocorm - like body (PLB) organogenesis could be coordinated by the removal of TDZ in callus maintenance medium. These results might contribute to elucidate the complex mechanism that leads to vanilla callus differentiation and subsequent shoot formation into PLB organogenesis. Moreover, our results highlight an early intermediate metabolic event in vanillin biosynthetic pathway with respect to secondary metabolism. Indeed, for the first time in vanilla tissue culture, phenolic compounds such as glucoside A and glucoside B were identified. The degradation of these compounds in specialized tissue (i.e. young green beans) probably contributes to the biosynthesis of glucovanillin, the parent compound of vanillin.</p