Variabilité génétique du nombre de cellules épidermiques de l’hypocotyle dans l’embryon et identification des QTL contrôlant ce caractère chez la Légumineuse modèle Medicago truncatula

National audienc

Cellular changes during Medicago truncatula hypocotyl growth depend on temperature and genotype.

Hypocotyl growth is a key characteristic for plant emergence, influenced by environmental conditions, particularly temperature, and varying among genotypes. Cellular changes in Medicago truncatula hypocotyl were characterized to study the impact of the environment on heterotrophic growth and analyze differences between genotypes. The number and length of epidermal cells, ploidy levels, and sugar contents were measured in hypocotyls grown in the dark at 20 °C and 10 °C using two genotypes with contrasting maximum hypocotyl length. Hypocotyl elongation in the dark was due to cell elongation and not to an increase in cell number. A marked increase in cell ploidy level was observed just after germination and until mid elongation of the hypocotyl under all treatments. Larger ploidy levels were also observed in the genotype with the shorter hypocotyl and in cold conditions, but they were associated with larger cells. The increase in ploidy level and in cell volume was concomitant with a marked increase in glucose and fructose contents in the hypocotyl. Finally, differences in hypocotyl length were mainly due to different number of epidermal cells in the seed embryo, shown as a key characteristic of genotypic differences, whereas temperature during hypocotyl growth affected cell volume

Combined ecophysiological and transcriptomic analysis of Medicago truncatula seedling growth in cold conditions

International audienc

Effects of cytokinins on secondary somatic embryogenesis of selected clone Rayong 9 of Manihot esculenta Crantz for ethanol production

In 2005, the Rayong-FCRC released a new high-yielding cassava cultivar designated Rayong 9 (R9) for ethanol production. However, the rate of distribution to farmers has been limited by the traditional vegetative propagation method of this crop which does not always satisfy the needs in planting material. The objective was to improve secondary somatic embryogenesis of the cassava clone Rayong 9 (R9) selected in Thailand by the Rayong Field Crops Research Center (Rayong-FCRC) for its suitability to produce ethanol. Fragments of cotyledon-stage somatic embryos were subcultured onto MS medium supplemented with the auxin 2,4-dichlorophenoxyacetic acid (2,4-D) at 4 mg/l in sight of inducing secondary somatic embryogenesis. Five different cytokinins, 6-benzylaminopurine (BAP), kinetin, zeatin, isopentenyladenine (2-iP) and adenine were added at 1 mg/l to the induction and maturation media to test their efficiency. Onto cytokinin-free media, 70 to 80% of explants produced embryoids, each explant giving 2 to 4 new embryoids within 7 weeks. The conversion rate of the embryoids into plantlets ranged from 11 to 26% depending on the type of cytokinin. With the exception of adenine, the other cytokinins inhibited the intensity of somatic embryogenesis, by 75% in the case of zeatin and 30% in the case of kinetin. Addition of adenine did not significantly improve the number of embryoids per explant. However, at 10, 20 and 40 mg/l adenine tended to improve the process relatively to embryoid sizes and plantlet survival rates in the greenhouse.Key words: Adenine, biofuel, cassava, cotyledonary-stage, embryoids, icrocuttings, micropropagation

Inhibition of PaCaMKII-E isoform in the dorsal unpaired median neurosecretory cells of cockroach reduces nicotine- and clothianidin-induced currents

Cellular responses to Ca(2+) require intermediary proteins such as calcium/calmodulin-dependent protein kinase II (CaMKII), which transduces the signal into downstream effects. We recently demonstrated that the cockroach genome encodes five different CaMKII isoforms, and only PaCaMKII-E isoform is specifically expressed in the dorsal unpaired median neurosecretory cells. In the present study, using antisense oligonucleotides, we demonstrated that PaCaMKII-E isoform inhibition reduced nicotine-induced currents through alpha-bungarotoxin-sensitive and -insensitive nicotinic acetylcholine receptor subtypes. Specifically, PaCaMKII-E isoform is sufficient to repress nicotinic current amplitudes as a result of its depression by antisense oligonucleotides. Similar results were found using the neonicotinoid insecticide clothianidin, which acted as a full agonist of dorsal unpaired median neuron nicotinic acetylcholine receptors. Clothianidin current amplitudes are strongly reduced under bath application of PaCaMKII-E antisense oligonucleotides but no significant results are found with alpha-bungarotoxin co-applied, demonstrating that CaMKII-E isoform affects nicotine currents through alpha-bungarotoxin-sensitive and -insensitive receptor subtypes whereas clothianidin currents are reduced via alpha-bungarotoxin-insensitive receptors. In addition, we found that intracellular calcium increase induced by nicotine and clothianidin were reduced by PaCaMKII-E antisense oligonucleotides, demonstrating that intracellular calcium increase induced by nicotine and clothianidin are affected by PaCaMKII-E inhibition. Cellular responses to Ca(2+) require intermediary proteins such as calcium/calmodulin-dependent protein kinase II (CaMKII). We recently demonstrated that the cockroach genome encodes five different CaMKII isoforms and only PaCaMKII-E isoform was specifically expressed in the dorsal unpaired median neurosecretory cells. Here we show that specific inhibition of PaCaMKII-E isoform is associated with a decrease in nicotine- and clothianidin-induced currents. In addition, analysis of calcium changes demonstrates that PaCaMKII-E inhibition induces a decrease in intracellular calcium concentration

Cell elongation instead cell number becomes the predominant factor influencing genotypic differences in Medicago truncatula hypocotyl length under abiotic stress

International audienc

The Arabidopsis thaliana-Alternaria brassicicola pathosystem: A model interaction for investigating seed transmission of necrotrophic fungi

Seed transmission constitutes a major component of the parasitic cycle for several fungal pathogens. However, very little is known concerning fungal or plant genetic factors that impact seed transmission and mechanisms underlying this key biological trait have yet to be clarified. Such lack of available data could be probably explained by the absence of suitable model pathosystem to study plant-fungus interactions during the plant reproductive phase