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Stage:105
From Master 2 Recherche Biosciences Végétales
Laboratoire d'accueil : LRSV
Equipe d'accueil : Evolution et Expression des Peroxydases
Encadrant(e)(s) : Christophe Dunand dunand@lrsv.ups-tlse.fr
Context:
Germination is controlled by external factors such as temperature, water and light and by hormone balance. Recently, reactive oxygen species (ROS) have been shown to act as messengers during plant development, stress responses and programmed cell death. We analyzed the role of ROS during germination and investigated the possibility for ROS being signalling molecules in this process.
Reactive oxygen species (ROS, e.g. superoxide (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (.OH•)) are by-products constantly produced during normal metabolic processes and the level of these cell-damaging compounds need to be controlled. ROS can also be produced for a specific purpose such as oxidative burst during plant defence. In particular, ROS released by the embryo through the seed coat have an important role in protecting the emerging embryo against pathogen attacks (Schopfer et al., 2001). They also play a major role in physiological processes such as root elongation through their action in cell wall loosening (Dunand et al., 2007) but also during seed germination and dormancy break (Ogawa and Iwabuchi, 2001; Sarath et al., 2007). Interestingly, several data suggest that ROS act as signalling molecules in plants during defence responses, stress responses and programmed cell death (Gechev and Hille, 2005; Laloi et al., 2007; Miller et al., 2007; Neill et al., 2002)
We showed that ROS are released prior to endosperm rupture, that ROS production is required for germination, and that class III peroxidases could be implicated in the spacio-temporal regulation of ROS production. H2O2 modifies the expression of genes specifically active during germination encoding for enzymes regulating ROS levels, pointing out a regulatory feed back loop for ROS production. Measurements of endogenous levels of ROS following application of GA and ABA suggested that ABA inhibits germination by repressing ROS accumulation, and that, conversely, GA triggers germination by promoting an increase of ROS levels.
Objectives
Using Arabidopsis thaliana as model, the main objectives of the projects are
(i) to identify which peroxidases are necessary for early germination steps. This point will require data mining and in silico analysis.
(ii) to study the peroxidases transcripts during first steps of germination by qPCR.
(iii) Genotyping and phenotyping of mutants for identified candidate.