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Nicolas Bouché

Publications and source records attributed to Nicolas Bouché.

8 recordsLinked to original sources
PubMed2006

An antagonistic function for Arabidopsis DCL2 in development and a new function for DCL4 in generating viral siRNAs.

Plants contain more DICER-LIKE (DCL) enzymes and double-stranded RNA binding (DRB) proteins than other eukaryotes, resulting in increased small RNA network complexities. Analyses of single, double, triple and quadruple dcl mutants exposed DCL1 as a sophisticated enzyme capable of producing both microRNAs (miRNAs) and siRNAs, unlike the three other DCLs, which only produce siRNAs. Depletion of siRNA-specific DCLs results in unbalanced small RNA levels, indicating a redeployment of DCL/DRB complexes. In particular, DCL2 antagonizes the production of miRNAs and siRNAs by DCL1 in certain circumstances and affects development deleteriously in dcl1 dcl4 and dcl1 dcl3 dcl4 mutant plants, whereas dcl1 dcl2 dcl3 dcl4 quadruple mutant plants are viable. We also show that viral siRNAs are produced by DCL4, and that DCL2 can substitute for DCL4 when this latter activity is reduced or inhibited by viruses, pointing to the competitiveness of DCL2. Given the complexity of the small RNA repertoire in plants, the implication of each DCL, in particular DCL2, in the production of small RNAs that have no known function will constitute one of the next challenges.

Arabidopsis↗
PubMed2006

DRB4-dependent TAS3 trans-acting siRNAs control leaf morphology through AGO7.

trans-acting siRNAs (ta-siRNAs) are endogenous RNAs that direct the cleavage of complementary mRNA targets . TAS gene transcripts are cleaved by miRNAs; the cleavage products are protected against degradation by SGS3, copied into dsRNA by RDR6, and diced into ta-siRNAs by DCL4 . We describe hypomorphic rdr6 and sgs3 Arabidopsis mutants, which do not exhibit the leaf developmental defects observed in null mutants and which, like null alleles, are impaired in sense-transgene-induced posttranscriptional gene silencing and virus resistance. Null rdr6 and sgs3 mutants lack TAS1, TAS2, and TAS3 ta-siRNAs and overaccumulate ARF3/ETTIN and ARF4 mRNAs, which are TAS3 ta-siRNA targets. A hypomorphic rdr6 mutant accumulates wild-type TAS3 ta-siRNA levels but not TAS1 and TAS2 ta-siRNAs, suggesting that TAS3 is required for proper leaf development. Consistently, tas3 but not tas1 or tas2 mutants exhibits leaf morphology defects, and ago7/zip and drb4 mutants, which exhibit leaf morphology defects, lack TAS3 but not TAS1 and TAS2 ta-siRNAs in leaves. These results indicate that the dsRNA binding protein DRB4 is required for proper ta-siRNA production, presumably by interacting with DCL4, an interaction analogous to that of HYL1 with DCL1 during miRNA production , and that TAS3 ta-siRNAs are required for proper leaf development through the action of AGO7/ZIPPY.

Alleles↗
PubMed2005

Plant-specific calmodulin-binding proteins.

Calmodulin CaM is the most prominent Ca2+ transducer in eukaryotic cells, regulating the activity of numerous proteins with diverse cellular functions. Many features of CaM and its downstream targets are similar in plants and other eukaryotes. However, plants possess a unique set of CaM-related proteins, and several unique CaM target proteins. This review discusses recent progress in identifying plant-specific CaM-binding proteins and their roles in response to biotic and abiotic stresses and development. The review also addresses aspects emerging from recent structural studies of CaM interactions with target proteins relevant to plants.

Calcium↗
PubMed2004

The root-specific glutamate decarboxylase (GAD1) is essential for sustaining GABA levels in Arabidopsis.

In plants, as in most eukaryotes, glutamate decarboxylase catalyses the synthesis of GABA. The Arabidopsis genome contains five glutamate decarboxylase genes and one of these genes (glutamate decarboxylase1; i.e. GAD1 ) is expressed specifically in roots. By isolating and analyzing three gad1 T-DNA insertion alleles, derived from two ecotypes, we investigated the potential role of GAD1 in GABA production. We also analyzed a promoter region of the GAD1 gene and show that it confers root-specific expression when fused to reporter genes. Phenotypic analysis of the gad1 insertion mutants revealed that GABA levels in roots were drastically reduced compared with those in the wild type. The roots of the wild type contained about sevenfold more GABA than roots of the mutants. Disruption of the GAD1 gene also prevented the accumulation of GABA in roots in response to heat stress. Our results show that the root-specific calcium/calmodulin-regulated GAD1 plays a major role in GABA synthesis in plants under normal growth conditions and in response to stress.

Arabidopsis↗
PubMed2003

Mitochondrial succinic-semialdehyde dehydrogenase of the gamma-aminobutyrate shunt is required to restrict levels of reactive oxygen intermediates in plants.

The gamma-aminobutyrate (GABA) shunt is a metabolic pathway that bypasses two steps of the tricarboxylic acid cycle, and it is present in both prokaryotes and eukaryotes. In plants the pathway is composed of the calcium/calmodulin-regulated cytosolic enzyme glutamate decarboxylase and the mitochondrial enzymes GABA transaminase and succinic-semialdehyde dehydrogenase (SSADH). The activity of the GABA shunt in plants is rapidly enhanced in response to various biotic and abiotic stresses. However the physiological role of this pathway remains obscure. To elucidate its role in plants, we analyzed Arabidopsis T-DNA knockout mutants of SSADH, the ultimate enzyme of the pathway. Four alleles of the ssadh mutation were isolated, and these exhibited a similar phenotype. When exposed to white light (100 micromol of photons per m2 per s), they appear dwarfed with necrotic lesions. Detailed spectrum analysis revealed that UV-B has the most adverse effect on the mutant phenotype, whereas photosynthetic active range light has a very little effect. The ssadh mutants are also sensitive to heat, as they develop necrosis when submitted to such stress. Moreover, both UV and heat cause a rapid increase in the levels of hydrogen peroxide in the ssadh mutants, which is associated with enhanced cell death. Surprisingly, our study also shows that trichomes are hypersensitive to stresses in ssadh mutants. Our work establishes a role for the GABA shunt in preventing the accumulation of reactive oxygen intermediates and cell death, which appears to be essential for plant defense against environmental stress.

Aldehyde Oxidoreductases↗
PubMed2003

GABA signaling: a conserved and ubiquitous mechanism.

In plants, research on gamma-aminobutyric acid (GABA) has focused on its role as a metabolite, mainly in the context of responses to biotic and abiotic stresses. By contrast, studies of GABA in vertebrates have concentrated mainly on its role as a neurotransmitter and signaling molecule. Here, we discuss recent findings that point towards a possible role for GABA as a signaling molecule in plants.

Arabidopsis↗
PubMed2002

A novel family of calmodulin-binding transcription activators in multicellular organisms.

Screening of cDNA expression libraries derived from plants exposed to stress, with 35S-labeled recombinant calmodulin as a probe, revealed a new family of proteins containing a transcription activation domain and two types of DNA-binding domains designated the CG-1 domain and the transcription factor immunoglobulin domain, ankyrin repeats, and a varying number of IQ calmodulin-binding motifs. Based on domain organization and amino acid sequence comparisons, similar proteins, with the same domain organization, were identified in the genomes of other multicellular organisms including human, Drosophila, and Caenorhabditis, whereas none were found in the complete genomes of single cell eukaryotes and prokaryotes. This family of proteins was designated calmodulin-binding transcription activators (CAMTAs). Arabidopsis thaliana contains six CAMTA genes (AtCAMTA1-AtCAMTA6). The transcription activation domain of AtCAMTA1 was mapped by testing a series of protein fusions with the DNA-binding domain of the bacterial LexA transcription factor and two reporter genes fused to LexA recognition sequences in yeast cells. Two human proteins designated HsCAMTA1 and HsCAMTA2 were also shown to activate transcription in yeast using the same reporter system. Subcellular fractionation of Arabidopsis tissues revealed the presence of CAMTAs predominantly in the nucleus. Calmodulin binding assays identified a region of 25 amino acids capable of binding calmodulin with high affinity (K(d) = 1.2 nm) in the presence of calcium. We suggest that CAMTAs comprise a conserved family of transcription factors in a wide range of multicellular eukaryotes, which possibly respond to calcium signaling by direct binding of calmodulin.

Amino Acid Motifs↗