Environmental conditions affect the formation of apoplastic barriers (endodermis and exodermis) in roots. This was shown on many species in many research papers. The exodermal layer is more variable in response to stress conditions than endodermal layer. Cadmium toxicity, as many other stresses, induces faster development of apoplastic barriers. Most of research papers published so far, however characterized only the response of main root to this type of stress factor. Lateral roots, an important part of the root system absorptive surface, are neglected and there is not much information about their response to cadmium stress. The pattern of apoplastic barriers development was therefore analysed in main and also in lateral roots of various size and position on maternal root axis. We found significant differences in response to cadmium stress among these different root types. Then we summed up the differences between these types of roots. Short lateral roots were generally more responsive to cadmium stress, cadmium affected root branching as well as differentiation of apoplastic barriers in lateral roots. These results help us to better understand the response of complex roots system to environmental conditions. In the second part of this work, the role of CASP genes in exodermal development was...

La graine est une structure de dissémination et de résistance jouant un rôle clé dans la vie de laplante. L’arabette des dames (Arabidopsis thaliana) et le maïs (Zea Mays) sont deux espècesmodèles étudiées pour le développement de la graine. Leurs graines possèdent deuxcompartiments filiaux : l’embryon (la future plante) et l’albumen (un compartiment deréserves). Le développement normal de la graine passe par une coordination entre ces deuxcompartiments qui implique des communications étroites (nutritionnelles, signalisations) à leurinterface. L’interface embryon/albumen est constituée des couches cellulaires externes del’embryon et de l’albumen ainsi que de structures apoplastiques les séparant telles que lacuticule et la gaine embryonnaire chez l’arabette. Dans une première partie, une analysetranscriptomique des tissus à l’interface embryon/albumen chez le maïs a permis d’identifierune nouvelle région se composant des couches d’albumen amylacé au contact de l’embryon.En parallèle, nous avons utilisé la technologie CRISPR/Cas9 pour cibler des gènes candidatspotentiellement impliqués dans la communication albumen/embryon. Dans une seconde partie,la fonction et les caractéristiques de la gaine embryonnaire, produite par l’albumen et déposéeà la surface de l’embryon ont été étudiées chez l’arabette. Nous avons montré que cette structurese maintient sur la plantule après germination ce qui va à l’encontre de la vision classiqueconsidérant la cuticule comme la couche la plus externe de la jeune plantule. Une approche demicroscopie à force atomique couplée à des caractérisations de mutants, a permis de montrerque cette gaine a de fortes propriétés antiadhésives aidant à la germination. Dans une dernièrepartie, la voie de signalisation permettant le contrôle de l’intégrité de la cuticule chez l’arabettea été complétée par la découverte d’un peptide, produit par l’embryon, clivé dans l’albumen etliant des récepteurs dans l’embryon déclenchant la fermeture des trous de la cuticule et laformation d’une structure continue et fonctionnelle. / Angiosperm seeds comprise two zygotic compartments generated by double fertilization: theembryo, which will give the future plant, and the endosperm which surrounds and nourishesthe embryo. Harmonious seed development requires the coordination and cooperation of thesetwo compartments, implicating an intricate and sustained communication at their interface. Theaim of this thesis was to characterize some of the important characteristics of this interface inthe two model species Arabidopsis thaliana and maize (Zea Mays). The embryo/endosperminterface is formed by the external cell layers of the embryo and by the endosperm cellsimmediately adjacent to the embryo. These cell populations contribute to specific apoplasticstructures such as the embryonic cuticle and the embryo sheath in Arabidopsis. However, littleis known about this interface in maize. In a first part of this thesis, transcriptomic analysis ofembryo/endosperm interface in maize coupled with in situ hybridization has led to theidentification of a new endosperm domain composed of endosperm cell layers in immediatecontact with the expanding embryo, and potentially involved in nutrient movement between thetwo tissues. A reverse genetics approach has been developed based on CRISPR/Cas9technology to target candidate genes potentially involved in embryo/endospermcommunication. In the second part of the thesis, the function and characteristics of the embryosheath, produced by the endosperm and deposited on embryo surface, have been investigatedin Arabidopsis. The maintenance of the sheath on seedlings post germination has beendemonstrated, contradicting the classical view that the cuticle forms the most external structureon the seedling at germination. Atomic force microscopy and phenotypic characterization ofmutants demonstrate the strong anti-adhesive properties of the sheath, which facilitatecotyledon escape during germination. In a last part of the thesis, the apoplastic signallingpathway controlling cuticle integrity in Arabidopsis has been completed by the identificationof a peptide, produced by the embryo, and cleaved by an endosperm-specific protease, whichbinds to receptors at the embryo surface, leading to the closure of gaps in the cuticle and thegeneration of a continuous and functional structure.

in English The apoplastic barriers of the root (endodermis and exodermis) represent an important regulatory mechanism for the uptake of water and nutrients from the environment, ensuring its selectivity. In addition, both layers respond to stress factors by altering its rate and degree of cell wall modification, which affects the transport properties of the root and represents adaptive plants to high heterogeneity of the soil environment. Apoplastic barriers also respond to the availability of mineral nutrients. This issue has recently been intensively studied and a number of ambiguities persist. Interestingly, the deficiency of some mineral nutrients stimulates the differentiation of barriers, while the deficiency of other mineral nutrients delays the differentiation. In addition, different plant species react differently to the deficiency of the same element. Another interesting aspect is the fact that the reaction of the endodermis and exodermis is localized and takes place mainly in that part of the root system which is directly exposed to the stress factor. This phenomenon has been observed with cadmium toxicity, but more recently with local nutrient deficiencies (nitrogen and potassium) in Zea mays. This diploma thesis deals with the functional significance of localized enhancing or delaying...