The MYST histone acetyltransferases are essential for gametophyte development in Arabidopsis

<p>Abstract</p> <p>Background</p> <p>Histone acetyltransferases (HATs) play critical roles in the regulation of chromatin structure and gene expression. Arabidopsis genome contains 12 HAT genes, but the biological functions of many of them are still unknown. In this work, we studied the evolutionary relationship and cellular functions of the two Arabidopsis HAT genes homologous to the MYST family members.</p> <p>Results</p> <p>An extensive phylogenetic analysis of 105 MYST proteins revealed that they can be divided into 5 classes, each of which contains a specific combination of protein modules. The two Arabidopsis MYST proteins, HAM1 and HAM2, belong to a "green clade", clearly separated from other families of HATs. Using a reverse genetic approach, we show that <it>HAM1 </it>and <it>HAM2 </it>are a functionally redundant pair of genes, as single Arabidopsis <it>ham1 </it>and <it>ham2 </it>mutants displayed a wild-type phenotype, while no double mutant seedling could be recovered. Genetic analysis and cytological study revealed that <it>ham1ham2 </it>double mutation induced severe defects in the formation of male and female gametophyte, resulting in an arrest of mitotic cell cycle at early stages of gametogenesis. RT-PCR experiments and the analysis of transgenic plants expressing the <it>GUS </it>reporter gene under the <it>HAM1 </it>or the <it>HAM2 </it>promoter showed that both genes displayed an overlapping expression pattern, mainly in growing organs such as shoots and flower buds.</p> <p>Conclusion</p> <p>The work presented here reveals novel properties for MYST HATs in Arabidopsis. In addition to providing an evolutionary relationship of this large protein family, we show the evidence of a link between MYST and gamete formation as previously suggested in mammalian cells. A possible function of the Arabidopsis MYST protein-mediated histone acetylation during cell division is suggested.</p

Involvement of Arabidopsis BIG protein in cell death mediated by Myo- Inositol homeostasis

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The Polyadenylation Factor Subunit CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30: A Key Factor of Programmed Cell Death and a Regulator of Immunity in Arabidopsis

Programmed cell death (PCD) is essential for several aspects of plant life, including development and stress responses. Indeed, incompatible plant-pathogen interactions are well known to induce the hypersensitive response, a localized cell death. Mutational analyses have identified several key PCD components, and we recently identified the mips1 mutant of Arabidopsis (Arabidopsis thaliana), which is deficient for the key enzyme catalyzing the limiting step of myoinositol synthesis. One of the most striking features of mips1 is the light-dependent formation of lesions on leaves due to salicylic acid (SA)-dependent PCD, revealing roles for myoinositol or inositol derivatives in the regulation of PCD. Here, we identified a regulator of plant PCD by screening for mutants that display transcriptomic profiles opposing that of the mips1 mutant. Our screen identified the oxt6 mutant, which has been described previously as being tolerant to oxidative stress. In the oxt6 mutant, a transfer DNA is inserted in the CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30 (CPSF30) gene, which encodes a polyadenylation factor subunit homolog. We show that CPSF30 is required for lesion formation in mips1 via SA-dependent signaling, that the prodeath function of CPSF30 is not mediated by changes in the glutathione status, and that CPSF30 activity is required for Pseudomonas syringae resistance. We also show that the oxt6 mutation suppresses cell death in other lesion-mimic mutants, including lesion-simulating disease1, mitogen-activated protein kinase4, constitutive expressor of pathogenesis-related genes5, and catalase2, suggesting that CPSF30 and, thus, the control of messenger RNA 3′ end processing, through the regulation of SA production, is a key component of plant immune responses

HSFA1a modulates plant heat stress responses and alters the 3D chromatin organization of enhancer-promoter interactions

The complex and dynamic three-dimensional organization of chromatin within the nucleus makes understanding the control of gene expression challenging, but also opens up possible ways to epigenetically modulate gene expression. Because plants are sessile, they evolved sophisticated ways to rapidly modulate gene expression in response to environmental stress, that are thought to be coordinated by changes in chromatin conformation to mediate specific cellular and physiological responses. However, to what extent and how stress induces dynamic changes in chromatin reorganization remains poorly understood. Here, we comprehensively investigated genome-wide chromatin changes associated with transcriptional reprogramming response to heat stress in tomato. Our data show that heat stress induces rapid changes in chromatin architecture, leading to the transient formation of promoter-enhancer contacts, likely driving the expression of heat-stress responsive genes. Furthermore, we demonstrate that chromatin spatial reorganization requires HSFA1a, a transcription factor (TF) essential for heat stress tolerance in tomato. In light of our findings, we propose that TFs play a key role in controlling dynamic transcriptional responses through 3D reconfiguration of promoter-enhancer contacts

Caractérisation fonctionnelle des histones acétyltransférases de la famille MYST et de l'histone désacétylase HDA9 chez arabidopsis thaliana

Les histones acétyltransférases (HAT) et les histones désacétylases (HDAC) sont des enzymes capables d acétyler et de désacétyler respectivement les histones, ainsi que certaines protéines non-histones. Elles agissent le plus souvent au sein de complexes multiprotéiques et jouent des rôles clés dans le remodelage de la chromatine, un mécanisme aujourd hui largement impliqué dans le contrôle du développement des plantes. L objectif de ce travail était d étudier le rôle des HAT de la famille MYST, HAM1 et HAM2, et de la HDAC HDA9 au cours du développement d Arabidopsis thaliana. Une analyse phylogénétique a permis de révéler l existence de plusieurs clades de protéines MYST. Par une démarche de génétique inverse, nous avons pu montrer que les deux représentants de la famille MYST chez Arabidopsis, HAM1 et HAM2, étaient fonctionnellement redondants. En plus de la mise en évidence de profils d expression similaires entre ces deux gènes, des analyses génétiques et des études cytologiques nous ont permis de révéler que la double mutation ham1 ham2 induisait des défauts importants dans la formation des gamétophytes mâles et femelles, résultant d un arrêt de la gamétogenèse dans des étapes précoces. Parallèlement, le rôle de la HDAC HDA9 dans le contrôle de la transition florale a été précisé. Par une approche de gènes candidats , nous avons révélé son rôle dans la répression de l activateur de la transition florale AGL19 via des modifications de la chromatine au niveau de son promoteur.Histone acetyltransferases (HAT) and histone deacetylases (HDAC) are enzymes able to respectively acetylate and deacetylate histone and non-histone protein. They usually act within multiprotein complexes and play key roles in chromatin remodeling, a mechanism that is greatly involved in the control of plant development. The aim of this work was to study the role of MYST family of HAT, HAM1 and HAM2, and HDAC HDA9 during the development of Arabidopsis thaliana. Phylogenetic analysis revealed the existence of several clades of MYST proteins. Using a reverse genetic approach, we showed that the two MYST family members in Arabidopsis, HAM1 and HAM2, were functionally redundant. In addition to show overlapping expression pattern between these two genes, genetic analysis and cytological studies revealed that ham1 ham2 double mutation induced severe defects in the formation of male and female gametophyte, resulting in an arrest of mitotic cell cycle at early stages of gametogenesis. At the same time, the role of the HDAC HDA9 in the control of flowering time has been specified. Using a candidate genes approach, we revealed its role in the repression of the floral activator AGL19 through chromatin modifications on its promoter.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Cristal mutations in Arabidopsis confer a genetically heritable, recessive, hyperhydric phenotype

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Texte de cadrage du symposium "Regards pluridisciplinaires sur les genres textuels et (audio)visuels comme modes de penser le monde et comme outils d'action

Ce texte de cadrage a pour fonction première de fournir des balises pour le dépôt des communications au symposium. Il propose, entre autres, deux définitions opérationnelles des "genres de discours" ou "genres de textes", qui pourront faire l'objet de discussions lors du symposium. Ce texte présente les genres textuels et médiatiques comme des produits culturels qui sont situés dans un temps et un espace donnés. Cette relation n'est pas unilatérale : si la société influence les genres textuels, ces derniers influencent également la société... Le texte propose aussi quelques questions-balises pour structurer le symposium ainsi que des références bibliographiques