Showing papers on "Mutant published in 2003"
TL;DR: Results indicate that both AtMYC2 and AtMYB2 proteins function as transcriptional activators in ABA-inducible gene expression under drought stress in plants.
Abstract: In Arabidopsis, the induction of a dehydration-responsive gene, rd22, is mediated by abscisic acid (ABA). We reported previously that MYC and MYB recognition sites in the rd22 promoter region function as cis-acting elements in the drought- and ABA-induced gene expression of rd22. bHLH- and MYB-related transcription factors, rd22BP1 (renamed AtMYC2) and AtMYB2, interact specifically with the MYC and MYB recognition sites, respectively, in vitro and activate the transcription of the β-glucuronidase reporter gene driven by the MYC and MYB recognition sites in Arabidopsis leaf protoplasts. Here, we show that transgenic plants overexpressing AtMYC2 and/or AtMYB2 cDNAs have higher sensitivity to ABA. The ABA-induced gene expression of rd22 and AtADH1 was enhanced in these transgenic plants. Microarray analysis of the transgenic plants overexpressing both AtMYC2 and AtMYB2 cDNAs revealed that several ABA-inducible genes also are upregulated in the transgenic plants. By contrast, a Ds insertion mutant of the AtMYC2 gene was less sensitive to ABA and showed significantly decreased ABA-induced gene expression of rd22 and AtADH1. These results indicate that both AtMYC2 and AtMYB2 proteins function as transcriptional activators in ABA-inducible gene expression under drought stress in plants.
1,931 citations
01 Jan 2003
TL;DR: A method called Synthetic Genetic Array (SGA) analysis was developed in this paper, which automates yeast genetics and enables a systematic and high- throughput construction of double mutants from an ordered array of ~4700 viable gene deletion mutants.
Abstract: budding yeast Saccharomyces cerevisiae, ~80% of the ~6000 genes are nonessential, indi- cating that many biological processes are buffered from the phenotypic consequences of genetic per- turbation. To examine these functional relation- ships we developed a method called Synthetic Genetic Array (SGA) analysis, which automates yeast genetics and enables a systematic and high- throughput construction of double mutants from an ordered array of ~4700 viable gene deletion mutants. In particular, double mutants showing reduced fitness (a synthetic sick phenotype) or lethality (a synthetic lethal phenotype) define functional relationships between genes and their corresponding pathways. We have undertaken a project to generate a synthetic genetic interaction network for the yeast cell with the expectation that it will represent a global map of functional relationships amongst most genes. We found that synthetic genetic interactions are more common than anticipated previously, with an average query gene displaying ~30 different interactions. Cluster analysis of a compendium of ~132 SGA screens revealed that genes displaying similar patterns of genetic interactions often encode proteins within the same pathway or complex; therefore, the yeast genetic interaction network predicts precise molec- ular roles of previously uncharacterized genes. Moreover, because a gene deletion mutation pro- vides a model for the effect of a compound that inhibits its corresponding gene product, our com- pendium of synthetic genetic profiles provides a key for determining the cellular targets of small molecules and drugs. Finally, the surprisingly large number of synthetic genetic interactions observed for defined mutations of inbred laboratory yeast strains suggests that digenic interactions of this type may also occur frequently amongst different alleles of genes found within the individuals of an outbred population and thus similar genetic inter- actions may underlie many of the inherited pheno- types in other organisms.
1,927 citations
TL;DR: It is found that in an uninduced state, NPR1 is present as an oligomer formed through intermolecular disulfide bonds, which provides a missing link between accumulation of SA and activation of NPR1 in the SAR signaling pathway.
1,402 citations
TL;DR: A surprisingly large fraction of these genes are unique to mycobacteria and closely related species, indicating that many of the strategies used by this unusual group of organisms are fundamentally different from other pathogens.
Abstract: Despite the importance of tuberculosis as a public health problem, we know relatively little about the molecular mechanisms used by the causative organism, Mycobacterium tuberculosis, to persist in the host. To define these mechanisms, we have mutated virtually every nonessential gene of M. tuberculosis and determined the effect disrupting each gene on the growth rate of this pathogen during infection. A total of 194 genes that are specifically required for mycobacterial growth in vivo were identified. The behavior of these mutants provides a detailed view of the changing environment that the bacterium encounters as infection proceeds. A surprisingly large fraction of these genes are unique to mycobacteria and closely related species, indicating that many of the strategies used by this unusual group of organisms are fundamentally different from other pathogens.
1,240 citations
TL;DR: P phenotypic analysis of the collection may produce essentially complete lists of genes required for diverse biological activities, as well as facilitate downstream studies of gene expression, protein localization, epistasis, and chromosome engineering.
Abstract: We have developed technologies for creating saturating libraries of sequence-defined transposon insertion mutants in which each strain is maintained. Phenotypic analysis of such libraries should provide a virtually complete identification of nonessential genes required for any process for which a suitable screen can be devised. The approach was applied to Pseudomonas aeruginosa, an opportunistic pathogen with a 6.3-Mbp genome. The library that was generated consists of 30,100 sequence-defined mutants, corresponding to an average of five insertions per gene. About 12% of the predicted genes of this organism lacked insertions; many of these genes are likely to be essential for growth on rich media. Based on statistical analyses and bioinformatic comparison to known essential genes in E. coli, we estimate that the actual number of essential genes is 300-400. Screening the collection for strains defective in two defined multigenic processes (twitching motility and prototrophic growth) identified mutants corresponding to nearly all genes expected from earlier studies. Thus, phenotypic analysis of the collection may produce essentially complete lists of genes required for diverse biological activities. The transposons used to generate the mutant collection have added features that should facilitate downstream studies of gene expression, protein localization, epistasis, and chromosome engineering.
1,089 citations
TL;DR: It is suggested that the level of the signal receptor, LasR, is a critical trigger for quorum-activated gene expression, and acyl-homoserine lactone quorum sensing appears to be a system that allows ordered expression of hundreds of genes during P. aeruginosa growth in culture.
Abstract: There are two interrelated acyl-homoserine lactone quorum-sensing-signaling systems in Pseudomonas aeruginosa. These systems, the LasR-LasI system and the RhlR-RhlI system, are global regulators of gene expression. We performed a transcriptome analysis to identify quorum-sensing-controlled genes and to better understand quorum-sensing control of P. aeruginosa gene expression. We compared gene expression in a LasI-RhlI signal mutant grown with added signals to gene expression without added signals, and we compared a LasR-RhlR signal receptor mutant to its parent. In all, we identified 315 quorum-induced and 38 quorum-repressed genes, representing about 6% of the P. aeruginosa genome. The quorum-repressed genes were activated in the stationary phase in quorum-sensing mutants but were not activated in the parent strain. The analysis of quorum-induced genes suggests that the signal specificities are on a continuum and that the timing of gene expression is on a continuum (some genes are induced early in growth, most genes are induced at the transition from the logarithmic phase to the stationary phase, and some genes are induced during the stationary phase). In general, timing was not related to signal concentration. We suggest that the level of the signal receptor, LasR, is a critical trigger for quorum-activated gene expression. Acyl-homoserine lactone quorum sensing appears to be a system that allows ordered expression of hundreds of genes during P. aeruginosa growth in culture.
1,082 citations
TL;DR: Observations provide direct evidence that endogenous SIRT1 protein regulates p53 acetylation and p53-dependent apoptosis, and show that the function of this enzyme is required for specific developmental processes.
Abstract: SIRT1 is a mammalian homolog of the Saccharomyces cerevisiae chromatin silencing factor Sir2 Dominant-negative and overexpression studies have implicated a role for SIRT1 in deacetylating the p53 tumor suppressor protein to dampen apoptotic and cellular senescence pathways To elucidate SIRT1 function in normal cells, we used gene-targeted mutation to generate mice that express either a mutant SIRT1 protein that lacks part of the catalytic domain or has no detectable SIRT1 protein at all Both types of SIRT1 mutant mice and cells had essentially the same phenotypes SIRT1 mutant mice were small, and exhibited notable developmental defects of the retina and heart, and only infrequently survived postnatally Moreover, SIRT1-deficient cells exhibited p53 hyperacetylation after DNA damage and increased ionizing radiation-induced thymocyte apoptosis In SIRT1-deficient embryonic fibroblasts, however, p53 hyperacetylation after DNA damage was not accompanied by increased p21 protein induction or DNA damage sensitivity Together, our observations provide direct evidence that endogenous SIRT1 protein regulates p53 acetylation and p53-dependent apoptosis, and show that the function of this enzyme is required for specific developmental processes
1,067 citations
TL;DR: It is proposed that γ-H2AX does not constitute the primary signal required for the redistribution of repair complexes to damaged chromatin, but may function to concentrate proteins in the vicinity of DNA lesions.
Abstract: Histone H2AX is rapidly phosphorylated in the chromatin micro-environment surrounding a DNA double-strand break (DSB). Although H2AX deficiency is not detrimental to life, H2AX is required for the accumulation of numerous essential proteins into irradiation induced foci (IRIF). However, the relationship between IRIF formation, H2AX phosphorylation (γ-H2AX) and the detection of DNA damage is unclear. Here, we show that the migration of repair and signalling proteins to DSBs is not abrogated in H2AX−/− cells, or in H2AX-deficient cells that have been reconstituted with H2AX mutants that eliminate phosphorylation. Despite their initial recruitment to DSBs, numerous factors, including Nbs1, 53BP1 and Brca1, subsequently fail to form IRIF. We propose that γ-H2AX does not constitute the primary signal required for the redistribution of repair complexes to damaged chromatin, but may function to concentrate proteins in the vicinity of DNA lesions. The differential requirements for factor recruitment to DSBs and sequestration into IRIF may explain why essential regulatory pathways controlling the ability of cells to respond to DNA damage are not abolished in the absence of H2AX.
1,012 citations
TL;DR: Dynamics and selection during biofilm formation were investigated by tagging the wild type and flagella/type IV mutants with Yfp and Cfp and performing time‐lapse confocal laser scanning microscopy in mixed colour biofilms, which revealed dynamic compositions with extensive motility, competition and selection occurring during development.
Abstract: Summary Biofilm formation by Gfp-tagged Pseudomonas aeruginosa PAO1 wild type, flagella and type IV pili mutants in flow chambers irrigated with citrate mini- mal medium was characterized by the use of confocal laser scanning microscopy and COMSTAT image anal- ysis. Flagella and type IV pili were not necessary for P. aeruginosa initial attachment or biofilm formation, but the cell appendages had roles in biofilm develop- ment, as wild type, flagella and type IV pili mutants formed biofilms with different structures. Dynamics and selection during biofilm formation were investi- gated by tagging the wild type and flagella/type IV mutants with Yfp and Cfp and performing time-lapse confocal laser scanning microscopy in mixed colour biofilms. The initial microcolony formation occurred by clonal growth, after which wild-type P. aeruginosa bacteria spread over the substratum by means of twitching motility. The wild-type biofilms were dynamic compositions with extensive motility, com- petition and selection occurring during development. Bacterial migration prevented the formation of larger microcolonial structures in the wild-type biofilms. The results are discussed in relation to the current model for P. aeruginosa biofilm development.
982 citations
TL;DR: AtNOS1 encodes a distinct nitric oxide synthase that regulates growth and hormonal signaling in plants and is a distinct enzyme with no sequence similarities to any mammalian isoform.
Abstract: Nitric oxide (NO) serves as a signal in plants. An Arabidopsis mutant (Atnos1) was identified that had impaired NO production, organ growth, and abscisic acid-induced stomatal movements. Expression of AtNOS1 with a viral promoter in Atnos1 mutant plants resulted in overproduction of NO. Purified AtNOS1 protein used the substrates arginine and nicotinamide adenine dinucleotide phosphate and was activated by Ca2+ and calmodulin-like mammalian endothelial nitric oxide synthase and neuronal nitric oxide synthase, yet it is a distinct enzyme with no sequence similarities to any mammalian isoform. Thus, AtNOS1 encodes a distinct nitric oxide synthase that regulates growth and hormonal signaling in plants.
878 citations
TL;DR: It is reported that EIN3 protein levels rapidly increase in response to ethylene and this response requires several ethylene-signaling pathway components including the ethylene receptors (ETR1 and EIN4), CTR1, Ein2, EIN5, and Ein6, and the ubiquitin/proteasome pathway.
TL;DR: Interactions between α-syn and tau can promote their fibrillization and drive the formation of pathological inclusions in human neurodegenerative diseases.
Abstract: Alpha-synuclein (alpha-syn) and tau polymerize into amyloid fibrils and form intraneuronal filamentous inclusions characteristic of neurodegenerative diseases. We demonstrate that alpha-syn induces fibrillization of tau and that coincubation of tau and alpha-syn synergistically promotes fibrillization of both proteins. The in vivo relevance of these findings is grounded in the co-occurrence of alpha-syn and tau filamentous amyloid inclusions in humans, in single transgenic mice that express A53T human alpha-syn in neurons, and in oligodendrocytes of bigenic mice that express wild-type human alpha-syn plus P301L mutant tau. This suggests that interactions between alpha-syn and tau can promote their fibrillization and drive the formation of pathological inclusions in human neurodegenerative diseases.
TL;DR: This high-resolution mutation analysis allows evaluation of previous predictions and hypotheses through interrelation of function, structure and mutation in the tumor suppressor p53.
Abstract: Inactivation of the tumor suppressor p53 by missense mutations is the most frequent genetic alteration in human cancers. The common missense mutations in the TP53 gene disrupt the ability of p53 to bind to DNA and consequently to transactivate downstream genes. However, it is still not fully understood how a large number of the remaining mutations affect p53 structure and function. Here, we used a comprehensive site-directed mutagenesis technique and a yeast-based functional assay to construct, express, and evaluate 2,314 p53 mutants representing all possible amino acid substitutions caused by a point mutation throughout the protein (5.9 substitutions per residue), and correlated p53 function with structure- and tumor-derived mutations. This high-resolution mutation analysis allows evaluation of previous predictions and hypotheses through interrelation of function, structure and mutation.
TL;DR: Yeast two-hybrid and plant overexpression studies show that EGL3, like GL3, interacts with TTG1, the myb proteins GL1, PAP1 and 2, CPC and TRY, and it will form heterodimers with GL3.
Abstract: GLABRA3 (GL3) encodes a bHLH protein that interacts with the WD repeat protein, TTG1. GL3 overexpression suppresses the trichome defect of the pleiotropic ttg1 mutations. However, single gl3 mutations only affect the trichome pathway with a modest trichome number reduction. A novel unlinked bHLH-encoding locus is described here, ENHANCER OF GLABRA3 (EGL3). When mutated, egl3 gives totally glabrous plants only in the gl3 mutant background. The double bHLH mutant, gl3 egl3, has a pleiotropic phenotype like ttg1 having defective anthocyanin production, seed coat mucilage production, and position-dependent root hair spacing. Furthermore, the triple bHLH mutant, gl3 egl3 tt8, phenocopies the ttg1 mutation. Yeast two-hybrid and plant overexpression studies show that EGL3, like GL3, interacts with TTG1, the myb proteins GL1, PAP1 and 2, CPC and TRY, and it will form heterodimers with GL3. These results suggest a combinatorial model for TTG1-dependent pathway regulation by this trio of partially functionally redundant bHLH proteins.
TL;DR: Data suggest that IRX5, IRX3, and IRX1 are all essential components of the cellulose synthesizing complex and the presence of all three subunits is required for the correct assembly of this complex.
Abstract: In a screen to identify novel cellulose deficient mutants, three lines were shown to be allelic and define a novel complementation group, irregular xylem5 (irx5). IRX5 was cloned and encodes a member of the CesA family of cellulose synthase catalytic subunits (AtCesA4). irx5 plants have an identical phenotype to previously described mutations in two other members of this gene family (IRX1 and IRX3). IRX5, IRX3, and IRX1 are coexpressed in exactly the same cells, and all three proteins interact in detergent solubilized extracts, suggesting that three members of this gene family are required for cellulose synthesis in secondary cell walls. The association of IRX1 and IRX3 was reduced to undetectable levels in the absence of IRX5. Consequently, these data suggest that IRX5, IRX3, and IRX1 are all essential components of the cellulose synthesizing complex and the presence of all three subunits is required for the correct assembly of this complex.
28 Nov 2003
TL;DR: The unicellular green alga Chlamydomonas offers a simple life cycle, easy isolation of mutants, and a growing array of tools and techniques for molecular genetic studies, among the principal areas of current investigation.
Abstract: The unicellular green alga Chlamydomonas offers a simple life cycle, easy isolation of mutants, and a growing array of tools and techniques for molecular genetic studies. Among the principal areas of current investigation using this model system are flagellar structure and function, genetics of basal bodies (centrioles), chloroplast biogenesis, photosynthesis, light perception, cell-cell recognition, and cell cycle control. A genome project has begun with compilation of expressed sequence tag data and gene expression studies and will lead to a complete genome sequence. Resources available to the research community include wild-type and mutant strains, plasmid constructs for transformation studies, and a comprehensive on-line database.
TL;DR: It is found that powdery mildew resistant 4 (pmr4), a mutant lacking pathogen-induced callose, became resistant to pathogens, rather than more susceptible, due to mutation of a callose synthase, resulting in a loss of the induced callose response.
Abstract: Plants attacked by pathogens rapidly deposit callose, a β-1,3-glucan, at wound sites. Traditionally, this deposition is thought to reinforce the cell wall and is regarded as a defense response. Surprisingly, here we found that powdery mildew resistant 4 (pmr4), a mutant lacking pathogen-induced callose, became resistant to pathogens, rather than more susceptible. This resistance was due to mutation of a callose synthase, resulting in a loss of the induced callose response. Double-mutant analysis indicated that blocking the salicylic acid (SA) defense signaling pathway was sufficient to restore susceptibility to pmr4 mutants. Thus, callose or callose synthase negatively regulates the SA pathway.
TL;DR: It is demonstrated here the importance of morphogenetic conversions in C. albicans pathogenesis, and an engineered strain in which this developmental transition can be externally modulated both in vitro and in vivo is constructed.
Abstract: It is widely assumed that the ability of Candida albicans to switch between different morphologies is required for pathogenesis. However, most virulence studies have used mutants that are permanently locked into either the yeast or filamentous forms which are avirulent but unsuitable for discerning the role of morphogenetic conversions at the various stages of the infectious process. We have constructed a strain in which this developmental transition can be externally modulated both in vitro and in vivo. This was achieved by placing one copy of the NRG1 gene (a negative regulator of filamentation) under the control of a tetracycline-regulatable promoter. This modified strain was then tested in an animal model of hematogenously disseminated candidiasis. Mice injected with this strain under conditions permitting hyphal development succumbed to the infection, whereas all of the animals injected under conditions that inhibited this transition survived. Importantly, fungal burdens were almost identical in both sets of animals, indicating that, whereas filament formation appears to be required for the mortality resulting from a deep-seated infection, yeast cells play an important role early in the infectious process by extravasating and disseminating to the target organs. Moreover, these infecting Candida yeast cells still retained their pathogenic potential, as demonstrated by allowing this developmental transition to occur at various time points postinfection. We demonstrate here the importance of morphogenetic conversions in C. albicans pathogenesis. This engineered strain should provide a useful tool in unraveling the individual contributions of the yeast and filamentous forms at various stages of the infectious process.
TL;DR: The analysis of the GPR54 mutant mice revealed developmental abnormalities of both male and female genitalia and histopathological changes in tissues which normally contain sexually dimorphic features, suggesting a role for GPR 54/KiSS-1 in normal sexual development.
TL;DR: It is concluded that GID2 is a positive regulator of GA signaling and that regulated degradation of SLR1 is initiated through GA-dependent phosphorylation and finalized by an SCFGID2-proteasome pathway.
Abstract: Gibberellin (GA) regulates growth and development in plants. We isolated and characterized a rice GA-insensitive dwarf mutant, gid2. The GID2 gene encodes a putative F-box protein, which interacted with the rice Skp1 homolog in a yeast two-hybrid assay. In gid2, a repressor for GA signaling, SLR1, was highly accumulated in a phosphorylated form and GA increased its concentration, whereas SLR1 was rapidly degraded by GA through ubiquitination in the wild type. We conclude that GID2 is a positive regulator of GA signaling and that regulated degradation of SLR1 is initiated through GA-dependent phosphorylation and finalized by an SCF(GID2)-proteasome pathway.
TL;DR: The DNA damage-dependent poly(ADP-ribose) polymerases, PARP1 and PARP-2, homo-and heterodimerize and are both involved in the base excision repair (BER) pathway as mentioned in this paper.
Abstract: The DNA damage-dependent poly(ADP-ribose) polymerases, PARP-1 and PARP-2, homo- and heterodimerize and are both involved in the base excision repair (BER) pathway. Here, we report that mice carrying a targeted disruption of the PARP-2 gene are sensitive to ionizing radiation. Following alkylating agent treatment, parp-2(-/-)-derived mouse embryonic fibroblasts exhibit increased post-replicative genomic instability, G(2)/M accumulation and chromosome mis-segregation accompanying kinetochore defects. Moreover, parp-1(-/-)parp-2(-/-) double mutant mice are not viable and die at the onset of gastrulation, demonstrating that the expression of both PARP-1 and PARP-2 and/or DNA-dependent poly(ADP-ribosyl) ation is essential during early embryogenesis. Interestingly, specific female embryonic lethality is observed in parp-1(+/-)parp-2(-/-) mutants at E9.5. Meta phase analyses of E8.5 embryonic fibroblasts highlight a specific instability of the X chromosome in those females, but not in males. Together, these results support the notion that PARP-1 and PARP-2 possess both overlapping and non-redundant functions in the maintenance of genomic stability.
TL;DR: Results from different experimental approaches sketches the outlines of a set of pleiotropic genes acting on a distributed system in the brain to produce the species-specific sequence of responses and actions.
Abstract: ▪ Abstract Courtship is a complex behavior in Drosophila that recruits a wide range of genes for its realization, including those concerning sex determination, ion channels, and circadian rhythms. Results from different experimental approaches—behavioral and genetic comparisons between species, analysis of mutants and mosaics, and identification of specific sensory stimuli—sketch the outlines of a set of pleiotropic genes acting on a distributed system in the brain to produce the species-specific sequence of responses and actions.
TL;DR: The distribution of late-flowering phenotypes in a mapping population segregating met1-1 indicates that the flowering-time phenotype is caused by the accumulation of inherited defects at loci unlinked to the met1 mutation, which led to a global reduction of cytosine methylation throughout the genome.
Abstract: We describe the isolation and characterization of two missense mutations in the cytosine-DNA-methyltransferase gene, MET1, from the flowering plant Arabidopsis thaliana. Both missense mutations, which affect the catalytic domain of the protein, led to a global reduction of cytosine methylation throughout the genome. Surprisingly, the met1-2 allele, with the weaker DNA hypomethylation phenotype, alters a well-conserved residue in methyltransferase signature motif I. The stronger met1-1 allele caused late flowering and a heterochronic delay in the juvenile-to-adult rosette leaf transition. The distribution of late-flowering phenotypes in a mapping population segregating met1-1 indicates that the flowering-time phenotype is caused by the accumulation of inherited defects at loci unlinked to the met1 mutation. The delay in flowering time is due in part to the formation and inheritance of hypomethylated fwa epialleles, but inherited defects at other loci are likely to contribute as well. Centromeric repeat arrays hypomethylated in met1-1 mutants are partially remethylated when introduced into a wild-type background, in contrast to genomic sequences hypomethylated in ddm1 mutants. ddm1 met1 double mutants were constructed to further our understanding of the mechanism of DDM1 action and the interaction between two major genetic loci affecting global cytosine methylation levels in Arabidopsis.
TL;DR: In this article, the authors used the vtc1 mutant to provide a molecular signature for vitamin C deficiency in plants and showed that 171 genes are expressed differentially in the mutant compared with the wild type and transcript changes indicate that growth and development are constrained by the modulation of abscisic acid signaling.
Abstract: Vitamin C deficiency in the Arabidopsis mutant vtc1 causes slow growth and late flowering. This is not attributable to changes in photosynthesis or increased oxidative stress. We have used the vtc1 mutant to provide a molecular signature for vitamin C deficiency in plants. Using statistical analysis, we show that 171 genes are expressed differentially in vtc1 compared with the wild type. Many defense genes are activated, particularly those that encode pathogenesis-related proteins. Furthermore, transcript changes indicate that growth and development are constrained in vtc1 by the modulation of abscisic acid signaling. Abscisic acid contents are significantly higher in vtc1 than in the wild type. Key features of the molecular signature of ascorbate deficiency can be reversed by incubating vtc1 leaf discs in ascorbate. This finding provides evidence that many of the observed effects on transcript abundance in vtc1 result from ascorbate deficiency. Hence, through modifying gene expression, vitamin C contents not only act to regulate defense and survival but also act via phytohormones to modulate plant growth under optimal conditions.
TL;DR: It is shown that glucose enhances the degradation of ETHYLENE-INSENSITIVE3 (EIN3), a key transcriptional regulator in ethylene signalling, through the plant glucose sensor hexokinase, and enhances the stability of EIN3.
Abstract: Glucose is a global regulator of growth and metabolism that is evolutionarily conserved from unicellular microorganisms to multicellular animals and plants In photosynthetic plants, glucose shows hormone-like activities and modulates many essential processes, including embryogenesis, germination, seedling development, vegetative growth, reproduction and senescence Genetic and phenotypic analyses of Arabidopsis mutants with glucose-insensitive (gin) and glucose-oversensitive (glo) phenotypes have identified an unexpected antagonistic interaction between glucose and the plant stress hormone ethylene The ethylene-insensitive etr1 and ein2 mutants have glo phenotypes, whereas the constitutive ethylene signalling mutant ctr1 is allelic to gin4 (refs 4, 5) The precise molecular mechanisms underlying the complex signalling network that governs plant growth and development in response to nutrients and plant hormones are mostly unknown Here we show that glucose enhances the degradation of ETHYLENE-INSENSITIVE3 (EIN3), a key transcriptional regulator in ethylene signalling, through the plant glucose sensor hexokinase Ethylene, by contrast, enhances the stability of EIN3 The ein3 mutant has a glo phenotype, and overexpression of EIN3 in transgenic Arabidopsis decreases glucose sensitivity
TL;DR: A different dwarfing mechanism found in maize brachytic2 (br2) mutants characterized by compact lower stalk internodes is described, which results from the loss of a P-glycoprotein that modulates polar auxin transport in the maize stalk.
Abstract: Agriculturally advantageous reduction in plant height is usually achieved by blocking the action or production of gibberellins. Here, we describe a different dwarfing mechanism found in maize brachytic2 (br2) mutants characterized by compact lower stalk internodes. The height reduction in these plants results from the loss of a P-glycoprotein that modulates polar auxin transport in the maize stalk. The sorghum ortholog of br2 is dwarf3 (dw3), an unstable mutant of long-standing commercial interest and concern. A direct duplication within the dw3 gene is responsible for its mutant nature and also for its instability, because it facilitates unequal crossing-over at the locus.
TL;DR: Results indicate that AtGRF proteins play a role in the regulation of cell expansion in leaf and cotyledon tissues in Arabidopsis thaliana.
Abstract: Summary
Previously, we identified a novel rice gene, GROWTH-REGULATING FACTOR1 (OsGRF1), which encodes a putative transcription factor that appears to play a regulatory role in stem elongation. We now describe the GRF gene family of Arabidopsis thaliana (AtGRF), which comprises nine members. The deduced AtGRF proteins contain the same characteristic regions—the QLQ (Gln, Leu, Gln) and WRC (Trp, Arg, Cys) domains—as do OsGRF1 and related proteins in rice, as well as features indicating a function in transcriptional regulation. Most of the AtGRF genes are strongly expressed in actively growing and developing tissues, such as shoot tips, flower buds, and roots, but weakly in mature stem and leaf tissues. Overexpression of AtGRF1 and AtGRF2 resulted in larger leaves and cotyledons, as well as in delayed bolting of the inflorescence stem when compared to wild-type plants. In contrast, triple insertional null mutants of AtGRF1–AtGRF3 had smaller leaves and cotyledons, whereas single mutants displayed no changes in phenotype and double mutants displayed only minor ones. The alteration of leaf growth in overexpressors and triple mutants was based on an increase or decrease in cell size, respectively. These results indicate that AtGRF proteins play a role in the regulation of cell expansion in leaf and cotyledon tissues.
TL;DR: Results show that GM3 ganglioside is a negative regulator of insulin signaling, making it a potential therapeutic target in type 2 diabetes, and protected from high-fat diet-induced insulin resistance.
Abstract: Gangliosides are sialic acid-containing glycosphingolipids that are present on all mammalian plasma membranes where they participate in recognition and signaling activities. We have established mutant mice that lack GM3 synthase (CMP-NeuAc:lactosylceramide α2,3-sialyltransferase; EC 2.4.99.-). These mutant mice were unable to synthesize GM3 ganglioside, a simple and widely distributed glycosphingolipid. The mutant mice were viable and appeared without major abnormalities but showed a heightened sensitivity to insulin. A basis for the increased insulin sensitivity in the mutant mice was found to be enhanced insulin receptor phosphorylation in skeletal muscle. Importantly, the mutant mice were protected from high-fat diet-induced insulin resistance. Our results show that GM3 ganglioside is a negative regulator of insulin signaling, making it a potential therapeutic target in type 2 diabetes.
TL;DR: It is concluded that D2/CYP90D2 catalyzes the steps from 6-deoxoteasterone to 3-dehydro-6- deoxoteastersone and from teasteroneto 3- dehydroteasterone in the late BR biosynthesis pathway.
Abstract: We characterized a rice dwarf mutant, ebisu dwarf (d2). It showed the pleiotropic abnormal phenotype similar to that of the rice brassinosteroid (BR)-insensitive mutant, d61. The dwarf phenotype of d2 was rescued by exogenous brassinolide treatment. The accumulation profile of BR intermediates in the d2 mutants confirmed that these plants are deficient in late BR biosynthesis. We cloned the D2 gene by map-based cloning. The D2 gene encoded a novel cytochrome P450 classified in CYP90D that is highly similar to the reported BR synthesis enzymes. Introduction of the wild D2 gene into d2-1 rescued the abnormal phenotype of the mutants. In feeding experiments, 3-dehydro-6-deoxoteasterone, 3-dehydroteasterone, and brassinolide effectively caused the lamina joints of the d2 plants to bend, whereas more upstream compounds did not cause bending. Based on these results, we conclude that D2/CYP90D2 catalyzes the steps from 6-deoxoteasterone to 3-dehydro-6-deoxoteasterone and from teasterone to 3-dehydroteasterone in the late BR biosynthesis pathway.
TL;DR: Although the resistance signaling in snc1 was fully dependent on PAD4, it was only partially affected by blocking salicylic acid synthesis, suggesting thatsnc1 activates both SA-dependent and SA-independent resistance pathways.
Abstract: Plants have evolved sophisticated defense mechanisms against pathogen infections, during which resistance (R) genes play central roles in recognizing pathogens and initiating defense cascades. Most of the cloned R genes share two common domains: the central domain, which encodes a nucleotide binding adaptor shared by APAF-1, certain R proteins, and CED-4 (NB-ARC), plus a C-terminal region that encodes Leu-rich repeats (LRR). In Arabidopsis, a dominant mutant, suppressor of npr1-1, constitutive 1 (snc1), was identified previously that constitutively expresses pathogenesis-related (PR) genes and resistance against both Pseudomonas syringae pv maculicola ES4326 and Peronospora parasitica Noco2. The snc1 mutation was mapped to the RPP4 cluster. In snc1, one of the TIR-NB-LRR–type R genes contains a point mutation that results in a single amino acid change from Glu to Lys in the region between NB-ARC and LRR. Deletions of this R gene in snc1 reverted the plants to wild-type morphology and completely abolished constitutive PR gene expression and disease resistance. The constitutive activation of the defense responses was not the result of the overexpression of the R gene, because its expression level was not altered in snc1. Our data suggest that the point mutation in snc1 renders the R gene constitutively active without interaction with pathogens. To analyze signal transduction pathways downstream of snc1, epistasis analyses between snc1 and pad4-1 or eds5-3 were performed. Although the resistance signaling in snc1 was fully dependent on PAD4, it was only partially affected by blocking salicylic acid (SA) synthesis, suggesting that snc1 activates both SA-dependent and SA-independent resistance pathways.