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International audience; The developmentally programmed loss of a plant organ is called abscission. This process is characterized by the ultimate separation of adjacent cells in the abscission zone (AZ). The discovery of an American oil palm (Elaeis oleifera) variant that does not shed its has allowed for the study of the mechanisms of ripe fruit abscission in this species. A comparative transcriptome analysis was performed to compare the fruit AZs of the non-shedding E. oleifera variant to an individual of the same progeny that sheds its ripe fruit normally. The study provides evidence for widespread perturbation to gene expression in the AZ of the non-shedding variant, compared to the normal fruit-shedding control, and offers insight into abscission-related functions. Beyond the genes with known or suspected roles during organ abscission or indehiscence that were identified, a list of genes with hormone-related functions, including ethylene, jasmonic acid, abscisic acid, cytokinin and salicylic acid, in addition to reactive oxygen species (ROS) metabolism, transcriptional responses and signaling pathways, was compiled. The results also allowed a comparison between the ripe fruit abscission processes of the African and American oil palm species at the molecular level and revealed commonalities with environmental stress pathways.

Additional file 1: Supplementary Fig. 1. Clusters AZ Overview of the four main clusters and multiple sub-clusters found by HCA analysis. Sub-clusters are labelled above the bars, while total number of contigs and percentage of each cluster are indicated at the left end of bars.

Additional file 2: Supplementary Fig. 2. (454 seq data Overview of sequencing results from the ethylene treatments)

International audience; BACKGROUND: A cryopreservation protocol has been established for oil palm somatic embryos (SEs), the efficiency of which must be evaluated, both in terms of regeneration and of long-term storage capacity, before its large-scale routine use.Objective: To test the survival and recovery of 29 clones of oil palm somatic embryos cryostored for 20 years.Materials and methods: Clumps of SEs were pregrown for 7 days on medium containing 0.75 M sucrose, dehydrated in air-tight containers containing silica gel to moisture contents between 19-35% fresh weight, and then immersed directly in liquid nitrogen and stored in cryotanks for 20 years.Results: Survival of SEs cryopreserved and rewarmed immediately displayed an average value of 19.1% for the 29 clones tested while survival of SEs rewarmed after 20 years of cryostorage was significantly higher, with an average of 33.2% for the 28 surviving clones. Out of these 28 surviving clones, three were lost due to contamination or regrowth decline, six produced only shoots and the rest proliferated.Conclusion: It is possible to cryostore oil palm SEs for extended periods and to regenerate proliferating cultures and plantlets from the cryopreserved material. The cryopreservation protocol established can thus be efficiently used to store oil palm germplasm and to manage large-scale production in industrial laboratories.

Recent research on the molecular and cellular mechanisms of fruit abscission of the tropical palm species Elaeis guineensis (African oil palm) and the function and original features of the fruit primary abscission zone (AZ1) will be presented. The AZ1 consists of approximately 10 cell layers in the boundary region between the pedicel (P) and mesocarp (M). During early fruit development, AZ1 cells are distinguishable from P and M cells by their smaller size and periclinal cell division orientation. AZ1 cell wall thickness increases earlier during development suggesting cell wall assembly occurs more rapidly in the AZ1 than adjacent P and M cells. AZ1 cells contain numerous intra-AZ1 layer plasmodesmata (PD), but very few inter-AZ1 layer PD, while nuclei are located adjacent to PD and are remarkably aligned within AZ1 layer cells, and remain aligned and intact after abscission. These cellular features allow a high capacity for intra-AZ1 layer signaling that may be important for AZ1 development and function for fruit abscission. A decrease in methylesterified homogalacturonan (the main pectin component of the middle lamella) and the expression of two AZ1 specific polygalacturonases are observed in AZ1 cell layers during abscission. A comprehensive transcriptome analysis of the AZ1, P and M tissues reveal specific AZ1 expression combined with overlapping expression patterns between the AZ1 and adjacent P and M tissues may be important for AZ1 functional specificity. These results provide a platform to study fruit abscission within the palm family to understand how this fundamental plant process has diversified during evolution.

International audience; The oil palm (Elaeis guineensis), a monocotyledonous species in the familyArecaceae, has an extraordinarily oil rich fleshy mesocarp, and presents an original model to examine the ripening processes and regulation in this particular monocot fruit. Histochemical analysis and cell parameter measurements revealed cell wall and middle lamella expansion and degradation during ripening and in response to ethylene. Cell wall related transcript profiles suggest a transition from synthesis to degradation is under transcriptional control during ripening, in particular a switch from cellulose, hemicellulose, and pectin synthesis to hydrolysis and degradation. The data provide evidence for the transcriptional activation of expansin, polygalacturonase, mannosidase, beta-galactosidase, and xyloglucan endotransglucosylase/hydrolase proteins in the ripening oil palm mesocarp, suggesting widespread conservation of these activities during ripening for monocotyledonous and eudicotyledonous fruit types. Profiling of the most abundant oil palm polygalacturonase (EgPG4) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) transcripts during development and in response to ethylene demonstrated both are sensitive markers of ethylene production and inducible gene expression during mesocarp ripening, and provide evidence for a conserved regulatory module between ethylene and cell wall pectin degradation. A comprehensive analysis of NAC transcription factors confirmed at least 10 transcripts from diverse NAC domain clades are expressed in the mesocarp during ripening, four of which are inducedby ethylene treatment, with the two most inducible (EgNAC6 and EgNAC7) phylogenetically similar to the tomato NAC-NOR master-ripening regulator. Overall, the results provide evidence that despite the phylogenetic distance of the oil palm within the family Arecaceae from the most extensively studied monocot banana fruit, it appearsripening of divergent monocot and eudicot fruit lineages are regulated by evolutionarily conserved molecular physiological processes.

La graine du palmier à huile (Elaeis guineensis Jacq.) est une graine albuminée constituée d'un embryon de très petite taille encapsule dans un albumen riche en lipides et en polysaccharides pariétaux. Il est accepté que son comportement en conservation soit de type intermédiaire, bien que le niveau de tolérance à la dessiccation de cette graine reste mal connu. La seule technologie pour la conservation à long terme des graines de palmier est donc la cryoconservation. De plus, cette graine possède une dormance particulière et le traitement utilise pour la lever (80 jours à 40°C) rend la mise au point de technologies de conservation très laborieuse chez cette espèce. Dans un premier temps, nous avons développé une technique de germination qui permet d'obtenir des résultats sur la survie des graines en seulement trois semaines. Nous avons également optimise les conditions de culture in vitro des embryons pour déterminer leur viabilité après traitement. Ces premiers essais sont informatifs quant à la nature de la dormance chez le palmier à huile. Ensuite, afin de connaitre la plage hydrique potentiellement utilisable en cryoconservation, le niveau de tolérance à la dessiccation des graines entières et des embryons a été mesure. Au sein de cette plage hydrique, l'embryon supporte sans dommage une immersion dans l'azote liquide sans pré-refroidissement contrôle, ce qui nous a permis de définir un premier protocole utilisable en routine pour la sauvegarde a long-terme des ressources génétiques de cette espèce. En revanche, l'albumen ne supporte pas une immersion directe dans l'azote liquide. Pour obtenir la survie de la graine entière et éviter la culture in vitro des embryons, un essai combinant quatre HR (humidité relative) de déshydratation, quatre vitesses et deux températures de pré-refroidissement, et deux vitesses de réchauffement a été mis en oeuvre. Les premiers résultats de cet essai seront présentes.

The lipid-rich fleshy mesocarp tissue of the oil palm (Elaeis guineensis) fruit is not only the main source of edible oil for the world, but it is also the richest dietary source of provitamin A. This study examines the transcriptional basis of these two outstanding metabolic characters in the oil palm mesocarp. Morphological, cellular, biochemical, and hormonal features defined key phases of mesocarp development. A 454 pyrosequencing derived transcriptome was then assembled for the developmental phases preceding and during maturation, when high rates of lipid and carotenoid biosynthesis occur. A total of 2,629 contigs with differential representation revealed coordination of metabolic and regulatory components. Further analysis focused on the fatty acid and triacylglycerol assembly pathways and during carotenogenesis. Notably, a contig similar to the Arabidopsis (Arabidopsis thaliana) seed oil transcription factor WRINKLED1 was identified with a transcript profile coordinated with those of several fatty acid biosynthetic genes and the high rates of lipid accumulation, suggesting some common regulatory features between seeds and fruits.

The oil palm (Elaeis guineensis), a monocotyledonous species in the family Arecaceae, has not only an extraordinarily oil rich fleshy mesocarp, and presents an original model to examine the ripening regulatory networks in a monocot fruit tissue. The final stage of ripening involves cell separation events in specialized tissue layers between the mesocarp and pedicel that leads to fruit shedding and seed dispersal. A two-stage abscission process involving primary and adjacent abscission zones (AZs), plus high levels of unmethylated pectin and polygalacturonase (PG) activity in the AZ, warrant further investigation. We have examined in more detai! the abscission processes of the oil palm fruit using a multidisciplinary approach and have discovered other originalities underlying oil palm fruit shedding. Overall, the data provide a basis to compare with the wellstudied dicot model fruit species, and suggest sorne conservation but also diversification has occurred in these processes between monocots and eudicots.

Oil palm (Elaeis guineensis) reproductive development includes original characteristics examined by our research group using multidisciplinary approaches, including large-scale transcriptome sequencing. Building on our research on flower development, in particular the roles of MADS-box genes, flower sex determination, fruit development and ripening are being investigated. The oil palm is monoecious, but described as temporally dioecious given that separate male and female inflorescences occur on the same palm at different times. To examine this character, transcriptome analysis of male and female flowers at early stages of development at which time sex is determined was performed. Once the female flower is pollinated, fruit development is initiated followed by ripening. The oil palm has an extraordinarily oil rich fleshy mesocarp, and presents an original model to examine the ripening regulatory networks in a monocot fruit. In addition, the mesocarp is also the richest dietary source of provitamin A. We have examined the transcriptomic basis of these two remarkable characters during mesocarp maturation and ripening. During ripening, a large increase in ethylene coincides with a coordinated regulation of ethylene biosynthesis and signaling transcripts, most notably, type VII ethylene response factor genes. Furthermore, MADS-box genes, including those encoding AGL2/SEPALLATA, AGAMOUS and GLOBOSA/PISTILLATA-like proteins, and their coordinated expression in the mesocarp, suggest differences between dicot and monocot fruit ripening. Finally, the final stage of ripening involves cell separation events in the base of the fruit. Overall, the data derived were used to construct a model to describe the maturation and ripening of the oil palm fruit. (Texte integral)

The oil palm (Elaeis guineensis), a monocotyledonous species in the family Arecaceae, has not only an extraordinarily oil rich fleshy mesocarp, and presents an original model to examine the ripening regulatory networks in a monocot fruit tissue. The final stage of ripening involves cell separation events in specialized tissue layers between the mesocarp and pedicel that leads to fruit shedding and seed dispersal. A two-stage abscission process involving primary and adjacent abscission zones (AZs), plus high levels of unmethylated pectin and polygalacturonase (PG) activity in the AZ, warrant further investigation. We have examined in more detai! the abscission processes of the oil palm fruit using a multidisciplinary approach and have discovered other originalities underlying oil palm fruit shedding. Overall, the data provide a basis to compare with the wellstudied dicot model fruit species, and suggest sorne conservation but also diversification has occurred in these processes between monocots and eudicots.