La paroi des cellules végétales subit des modifications afin de s'assouplir ou de se rigidifier selon les besoins de la plante. Cette paroi est une structure complexe, composée de cellulose, d'hémicellulose et de pectines. Les modifications subies par les pectines au cours de l'élongation cellulaire sont encore assez peu caractérisées. Dans ce contexte, le but de ce projet est d'étudier le rôle de deux polygalacturonases (PG) dans le développement racinaire de la plante modèle A. thaliana. Les PG sont des enzymes de dégradation des homogalacturonanes (HG), le composant pectique majoritaire de la paroi primaire. Notrehypothèse est que les PG dégradent partiellement les HG des parois longitudinales des cellules racinaires en élongation. Cette dégradation engendrerait un assouplissement pariétal localisé, permettant la croissance anisotropique des cellules. Nos résultats indiquent que les gènes des deux PG étudiées, nommés PG ROOT APICAL MERISTEM (PG RAM) et PG ROOT (PG R) sontexprimés de façon complémentaire dans la racine, l'un dans le méristème racinaire (PG RAM), et l'autre dans la zone d'élongation et de différenciation (PG R). De plus, la sur-expression de la protéine PG R entraine une augmentation de l’élongation des hypocotyles étiolés, ainsi qu'une augmentation de la densité de racines latérales par rapport au sauvage, démontrant son rôle dans le développement racinaire et dans l'allongement cellulaire. Enfin, nous avons démontré que l'expression des gènes de ces PG était contrôlée de façon différentielle par les facteurs de transcription de la famille PLETHORA (PLT). / Plant cell wall structure is modified to control its stiffness or flexibility according to plant’s requirements. The cell wall is a complex structure, composed of cellulose, hemicelluloses and pectins. Pectin modifications during cellular elongation are not very well characterized. In this context, the aim of this project is to study the roles of two polygalacturonases (PG) in the root development on the model plant A. thaliana. PG are homogalacturonans (HG) degradation enzymes, HG being the major pectic component of the primary cell wall. This degradation would lead to a local parietal relaxation, allowing anisotropic growth of the cells. Our results show that the two studied PG, named PG ROOT APICAL MERISTEM (PG RAM) and PG ROOT (PG R), are expressed in complementary areas of the root, either in the root apical meristem (PG RAM) or in the elongated and differenciated root tissues (PG R). Furthermore, the over-expression of PG R results in longer etiolated hypocotyls and increases root density when compared to wild-type, demonstrating its function in root development and in cell elongation. Finally, we demonstrated that expression of these two PG genes is under the control of PLETHORA (PLT) family transcription factors, by differentially ways

Submitted by Cássia Santos (cassia.bcufg@gmail.com) on 2015-01-30T10:50:40Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Alceny Garcia Filho - 2014.pdf: 2219421 bytes, checksum: 7bccfbe2cdaf663705c07a9d9017bda7 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-01-30T13:07:22Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Alceny Garcia Filho - 2014.pdf: 2219421 bytes, checksum: 7bccfbe2cdaf663705c07a9d9017bda7 (MD5) / Made available in DSpace on 2015-01-30T13:07:22Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Alceny Garcia Filho - 2014.pdf: 2219421 bytes, checksum: 7bccfbe2cdaf663705c07a9d9017bda7 (MD5) Previous issue date: 2014-08-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The work proposed aims to provide a reflection about the importance of promoting a dynamic teaching. Therefore it proposes the use of a software , A Plethora of Polyhedra, that considers the learning needs of students in order to assist them in the viewing and understanding of space around them and so they can use the geometric and mathematical knowledge in benefit of everyday issues. This is a free software for d ynamic mathematics that gathers resources of spatial geometry such as: rotation, translation, enlargement, reduction, and counting of the number of vertices, edges and faces, which enables the students understand the main presented contents. By manipulating the software chosen, teacher and student can identify their main characteristics and essential elements, not just only through the development and resolution of mathematical expressions algebraically presented. This work also is willing to motivate the activities to be proposed by a theoretical basis and analyze the possible difficulties encountered by students and teachers, and the opportunities for improvement in the teaching of geometry. / O trabalho ora proposto tem como objetivo proporcionar uma reflexão sobre a importância de se promover um ensino dinâmico. Para tanto, propõe -se a utilização de um software – Uma Pletora de Poliedros – que leve em consideração as necessidades de aprendizagem dos alunos, de modo a ajudá-los na visualização e no entendimento do espaço que os cerca e para que eles possam utilizar o conhecimento geométrico e matemático em benefício das questões cotidianas. Trata-se de um software livre para matemática dinâmica que reúne recursos de geometria espacial como: rotação, translação, ampliação, redução e contagem do número de vértices, arestas e faces, o que permite aos alunos compreenderem os principais conteúdos apresentados. Ao manipular o software escolhido, professor e aluno podem identificar suas principais características e elementos essenciais, não mais apenas somente por meio da elaboração e resolução de expressões matemáticas algebricamente apresentadas. Este trabalho dispõe-se, ainda, a motivar as atividades a serem propostas por meio de uma fundamentação teórica, bem como analisar as possíveis dificuldades encontradas por parte de alunos e professores, assim como as possibilidades de melhoria no ensino de geometria.