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.

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

Programmed cell death (PCD) is essential for several aspects of plant life. We previously identified the mips1 mutant of Arabidopsis thaliana, which is deficient for the enzyme catalysing myo-inositol synthesis, and that displays light-dependent formation of lesions on leaves due to Salicylic Acid (SA) over-accumulation. Rationale of this work was to identify novel regulators of plant PCD using a genetic approach.

Chloroplast Activity and 3'phosphadenosine 5'phosphate Signaling Regulate Programmed Cell Death in Arabidopsis.

Programmed cell death (PCD) is a crucial process both for plant development and responses to biotic and abiotic stress. There is accumulating evidence that chloroplasts may play a central role during plant PCD as for mitochondria in animal cells, but it is still unclear whether they participate in PCD onset, execution, or both. To tackle this question, we have analyzed the contribution of chloroplast function to the cell death phenotype of the myoinositol phosphate synthase1 (mips1) mutant that forms spontaneous lesions in a light-dependent manner.

Involvement of Arabidopsis Hexokinase1 in Cell Death Mediated by Myo-Inositol Accumulation.

Programmed cell death (PCD) is essential for several aspects of plant life, including development and stress responses. We recently identified the mips1 mutant of Arabidopsis thaliana, which is deficient for the enzyme catalyzing the limiting step of myo-inositol (MI) 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.

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.

The BAF60 subunit of the SWI/SNF chromatin-remodeling complex directly controls the formation of a gene loop at FLOWERING LOCUS C in Arabidopsis.

SWI/SNF complexes mediate ATP-dependent chromatin remodeling to regulate gene expression. Many components of these complexes are evolutionarily conserved, and several subunits of Arabidopsis thaliana SWI/SNF complexes are involved in the control of flowering, a process that depends on the floral repressor FLOWERING LOCUS C (FLC). BAF60 is a SWI/SNF subunit, and in this work, we show that BAF60, via a direct targeting of the floral repressor FLC, induces a change at the high-order chromatin level and represses the photoperiod flowering pathway in Arabidopsis.

Chromatin meets the cell cycle.

The cell cycle is one of the most comprehensively studied biological processes, due primarily to its significance in growth and development, and its deregulation in many human disorders. Studies using a diverse set of model organisms, including yeast, worms, flies, frogs, mammals, and plants, have greatly expanded our knowledge of the cell cycle and have contributed to the universally accepted view of how the basic cell cycle machinery is regulated. In addition to the oscillating activity of various cyclin-dependent kinase (CDK)-cyclin complexes, a plethora of proteins affecting various aspects of chromatin dynamics has been shown to be essential for cell proliferation during plant development.

Multiple functions of Kip-related protein5 connect endoreduplication and cell elongation.

Despite considerable progress in our knowledge regarding the cell cycle inhibitor of the Kip-related protein (KRP) family in plants, less is known about the coordination of endoreduplication and cell differentiation. In animals, the role of cyclin-dependent kinase (CDK) inhibitors as multifunctional factors coordinating cell cycle regulation and cell differentiation is well documented and involves not only the inhibition of CDK/cyclin complexes but also other mechanisms, among them the regulation of transcription. Interestingly, several plant KRPs have a punctuated distribution in the nucleus, suggesting that they are associated with heterochromatin.

Dual function of MIPS1 as a metabolic enzyme and transcriptional regulator.

Because regulation of its activity is instrumental either to support cell proliferation and growth or to promote cell death, the universal myo-inositol phosphate synthase (MIPS), responsible for myo-inositol biosynthesis, is a critical enzyme of primary metabolism. Surprisingly, we found this enzyme to be imported in the nucleus and to interact with the histone methyltransferases ATXR5 and ATXR6, raising the question of whether MIPS1 has a function in transcriptional regulation. Here, we demonstrate that MIPS1 binds directly to its promoter to stimulate its own expression by locally inhibiting the spreading of ATXR5/6-dependent heterochromatin marks coming from a transposable element.

The Arabidopsis ortholog of the YEATS domain containing protein YAF9a regulates flowering by controlling H4 acetylation levels at the FLC locus.

Histone acetylation and complexes associated with this process are directly involved in chromatin regulation and gene expression. Among these, NuA4 complex is directly involved in acetylation of histone H4, H2A and H2A.Z.

Histone acetyltransferase GCN5 interferes with the miRNA pathway in Arabidopsis.

MicroRNAs (miRNA) that guide sequence-specific posttranscriptional gene silencing play an important role in gene expression required for both developmental processes and responses to environmental conditions in plants. However, little is known about the transcriptional and posttranscriptional regulation of miRNA expression. Histone acetylation plays an important role in chromatin remodeling and is required for gene activation.

The MYST histone acetyltransferases are essential for gametophyte development in Arabidopsis.

Background: 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.

Characterization of a phosphatase 2C protein as an interacting partner of the histone acetyltransferase GCN5 in Arabidopsis.

Arabidopsis GCN5 is a major histone acetyltransferase. The mutation of the gene induces pleiotropic effects on plant development, and affects the expression of a large number of genes. The mechanism of action of this protein in controlling plant chromatin structure and genome expression is not understood.

MGOUN3: evidence for chromatin-mediated regulation of FLC expression.

The MGOUN3(MGO3)/BRUSHY1(BRU1)/TONSOKU(TSK) gene of Arabidopsis thaliana encodes a nuclear leucine-glycine-asparagine (LGN) domain protein that may be implicated in chromatin dynamics and genome maintenance. Mutants with defects in MGO3 display a fasciated stem and disorganized meristem structures. The transition to flowering was examined in mgo3 mutants and it was found that, under short days, the mutants flowered significantly earlier than the wild-type plants.

Regulation of meristem activity by chromatin remodelling.

The continuity and plasticity of plant development rely on the regulation of meristem activity in response to endogenous and environmental signals. Many plant development regulators involved in meristem function are transcription factors or signalling molecules. In the past few years, the role of chromatin remodelling in programming, maintaining or resetting specific gene expression profiles in subsequent cell generations has been shown to be crucial in plant development.

Arabidopsis HAF2 gene encoding TATA-binding protein (TBP)-associated factor TAF1, is required to integrate light signals to regulate gene expression and growth.

Plant growth and development are sensitive to light. Light-responsive DNA-binding transcription factors have been functionally identified. However, how transcription initiation complex integrates light signals from enhancer-bound transcription factors remains unknown.

MGOUN3, an Arabidopsis gene with TetratricoPeptide-Repeat-related motifs, regulates meristem cellular organization.

In order to understand the functioning of apical meristems in Arabidopsis more clearly, a new mutant, mgoun3 (mgo3), affected in the structural organization and the functional regulation of both shoot and root meristems has been isolated. mgo3 plants display perturbations in leaf morphogenesis, in the spatial and the temporal formation of primordia, and frequent fasciation of the inflorescence stem. Cellular analysis showed that both cellular organization and cell identity patterning are impaired in the mutant meristems.

Arabidopsis histone acetyltransferase AtGCN5 regulates the floral meristem activity through the WUSCHEL/AGAMOUS pathway.

Histone acetyltransferases, which are able to acetylate histone and non-histone proteins, play important roles in gene regulation. Many histone acetyltransferases are related to yeast Gcn5, a component of two transcription regulatory complexes SAGA and ADA. In this work, by characterizing a mutation in the Arabidopsis GCN5 gene (AtGCN5) we studied the regulatory function of this gene in controlling floral meristem activity.