Insights into the genetic determinism of pre-emergence growth using the model legume Medicago truncatula

Insights into the genetic determinism of pre-emergence growth using the model legume Medicago truncatula.Insights into the genetic determinism of pre-emergence growth using the model legume Medicago truncatula

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

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Bases génétiques de la croissance hétérotrophe en conditions optimales et sous stress abiotiques chez Medicago truncatula : contribution du nombre et de la longueur des cellules

La croissance hétérotrophe de l’hypocotyle est une étape clé pour la réussite de la levée. La présente étude est focalisée sur le déterminisme génétique de l’allongement de cet organe à l’obscurité chez Medicago truncatula en analysant le nombre et la longueur des cellules de l’épiderme, tissu gouvernant l’allongement des organes. Une grande variabilité génétique du nombre de cellules a été révélée dans les graines de 15 génotypes représentatifs de la diversité génétique de l’espèce. La stabilité de ce caractère dans des graines provenant de différentes productions suggère qu’il est sous contrôle génétique fort. Il a été montré que ce nombre de cellules, préétabli dans les graines, est le principal déterminant de la variation génotypique de la longueur de hypocotyle en conditions optimales de croissance. Par contre, l\u27élongation cellulaire devient le déterminant majeur des différences génotypiques observées sous stress abiotiques (basse température, déficit hydrique).Des loci contrôlant le nombre de cellules de l’épiderme et leur longueur maximale à basse température ont ensuite été identifiés dans une population de lignées recombinantes. Ceux ayant un impact sur l’élongation de l’hypocotyle à basse température ont été mis en évidence. Enfin, deux génotypes présentant un nombre de cellules similaire mais des capacités d’allongement cellulaire contrastées ont été plus finement comparés. Des protéines ayant un rôle dans la formation et l’organisation du cytosquelette et dans la modification des parois cellulaires ont été révélées en lien avec les différences d’allongem

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

Quantitative Trait Locus (QTL) involved in the resistance of barley (Hordeum vulgare L.) to the mildew under different water treatments, in semi-arid Mediterranean region

In the present study we evaluated the contribution of molecular marking to the breeding of barley ( Hordeum vulgare L.) for resistance to the mildew ( Erysiphe graminis sp L. hordei ) in semi-arid Mediterranean region. For this study a F8 progeny of 167 recombinants inbred lines (RILs) from two row barley was cultivated at the experimental station of the National Institute of Agronomic Research of Tunisia (INRAT), at Kef during the cropping season of 1999/2000. The trials, in a completely randomized design, were conducted under three water treatments: (1) irrigation at seedling emergence, (2) no water addition and (3) irrigation at first observation of water stress symptoms. Assessment of natural infection by mildew of was made every fifteen days starting from the day when water treatments were setup. Statistical analyses of data showed a high among progeny variation within the progeny of RILs regardless a water treatments; however plants of treatment 1 (irrigation since seedling emergence) appeared to be the most susceptible. A combination of data on susceptibility of barley to natural infection by mildew and data from the genetic map generated from the crossing of Er/Apm vs Tadmor (parents of the 167RILs) allowed the detection and localization of several QTLs on chromosomes 3(3H), 4(4H) and 7(5H) of the barley. The most significant QTLs were located on the longer arm of chromosome 4(4H); on a portion where several authors have located reaction genes of barley to E. graminis. Overall, our results showed that the detection of QTL responsible of the expression of the resistance to E. graminis seemed to be intimately linked to the initial cropping conditions (e.g. temperature and optimum humidity). Indeed, no primary QTL were observed for dry conditions treatment (no irrigation). Moreover, the available literature reports did not allow us to confirm the relative situations of the secondary QTLs found for these treatments. Thus, genes of resistance to E. graminis would express themselves only in conditions that are favorable for the development of the pathogen. Improving the resistance of barley to mildew infection requires therefore, by a good knowledge on the process that governs expression of these genes