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Accueil du site > Equipes de recherche > Peroxydases : évolution et expression > Thèmes de recherche > Functional studies of cell wall localized CIII peroxidases during Arabidopsis thaliana development

Functional studies of cell wall localized CIII peroxidases during Arabidopsis thaliana development

Contact : mail to Christophe DUNAND and mail to Philippe RANOCHA (Peroxidases : evolution and expression team)
mail to Vincent Burlat (Cell wall proteins and Development team)

Context
The 73 CIII Peroxidases from Arabidopsis thaliana display specific expression profiles during development and are predicted to be targeted to the vacuole or the cell wall whether they possess or not a C-terminus vacuolar targeting sequence (Francoz et al., 2014). Recent studies indicate that the fine localization of individual peroxidases within the cell wall could provide the mean for an accurate “enzyme-substrate” meeting allowing controlled enzymatic action within cell wall micro-domains. This action can conceptually implicate either a role in cell wall loosening or in cell wall stiffening (Figure).
We are currently studying the role of CIII peroxidases – mainly cell wall localized – particularly during two developmental processes leading to the seed formation and to its germination through a transversal project involving the “Peroxidases : evolution and expression” “Cell wall proteins and Development” teams. Candidate selection is primarily based upon a pre-selection through transcriptomic data analysis followed by a second step of systematic in situ RNA hybridization. The functional study of the selected candidates displaying a specific expression profile is mainly achieved through reverse genetics with a particular interest for the ultrastructural localization of candidate proteins and for microphenotyping.

Objectives
1°) Control of cell wall dynamics of seed mucilage secretory cells (MSCs) During embryogenesis, the 5 cell layers of seed coat are specialized with the outermost epidermal layer displaying a outstanding cell wall dynamism. Beside their primary cell wall, these cells develop a volcano-shaped internal secondary cell wall (the columella) and produce an abundant polysaccharidic mucilage that is compressed between the tangential primary cell wall and the columella. The role of this mucilage is only revealed during seed imbibitions several months-to-years later long after seed desiccation. Programmed localized cell wall stiffening and/or loosening events occurring during embryogenesis steps allow a polarized rupture of outer primary cell wall under the pressure of the hydrated mucilage. A mucilage pluristratified sheath decorates the seed favouring germination. We are currently studying the function, the regulation modes and the molecular targets of several CIII peroxidases during this developmental process.
2°) Control of micropylar endosperm rupture during germination The germination is controlled by external factors such as temperature, hydration and light and by hormonal equilibrium. Two major steps during germination are seed coat rupture and micropylar endosperm rupture allowing radicule protusion. Recently, the secondary messenger role of reactive oxygen species (ROS) has been demonstrated during this process (Lariguet et al., 2013). We demonstrated that ROS are produced before micropylar endosperm rupture, that ROS production is necessary for germination and that CIII peroxidases could be implicated in the spatio-temporal control of ROS production during germination. We are currently studying the function, the regulation modes and the molecular targets of several CIII peroxidases during this developmental process.