Project description:To optimize access to nitrogen under limiting conditions, root systems must continuously sense and respond to local or temporal fluctuations in nitrogen availability. In Arabidopsis thaliana and several other species, external N levels that induce only mild deficiency stimulate the emergence of lateral roots and especially the elongation of primary and lateral roots. However, the identity of the genes involved in this coordination remains still largely elusive. In order to identify novel genes and mechanisms underlying nitrogen-dependent root morphological changes, we investigated time-dependent changes in the root transcriptome of Arabidopsis thaliana plants grown under sufficient nitrogen or under conditions that induced mild nitrogen deficiency.
Project description:In this study, we used a cross-species network approach to uncover nitrogen (N)-regulated network modules conserved across a model and a crop species. By translating gene network knowledge from the data-rich model Arabidopsis (Arabidopsis thaliana, ecotype Columbia-0) to a crop, rice (Oryza sativa spp. japonica (Nipponbare)), we identified evolutionarily conserved N-regulatory modules as targets for translational studies to improve N use efficiency in transgenic plants.
Project description:To comprehensively investigate the effects of glutathione on the gene expression, the microarray analysis was performed in the glutathione-fed wild-type Arabidopsis thaliana. Wild-type Arabidopsis (ecotype Columbia-0) were fed with 1 mM oxidized glutathione (GSSG) and 2 mM reduced glutathione (GSH) for comparison at equal nitrogen equivalents. To examine the effects of glutathione other than nitrogen at equal nitrogen equivalents, plants were fed with 3 mM NH4NO3. Plants grown by water were used as a control.
Project description:RNA silencing is a mechanism for regulating gene expression at the transcriptional and post-transcriptional levels. Its functions include regulating endogenous gene expression and protecting the cell against viruses and invading transposable elements (TEs). A key component of the mechanism is small RNAs (sRNAs) of 21-24 nucleotides (nt) in length, which direct the silencing machinery in a sequence specific manner to target nucleic acids. sRNAs of 24 nt are involved in methylation of cytosine residues of target loci in three sequence contexts (CG, CHG and CHH), referred to as RNA-directed DNA methylation (RdDM). We previously demonstrated that 24 nt sRNAs are mobile from shoot to root in Arabidopsis thaliana. In this study we demonstrated that methylation of thousands of loci in root tissues is dependent upon mobile sRNAs from the shoot. Furthermore, we found that mobile sRNA-dependent DNA methylation occurs predominantly in non-CG contexts. These findings were made using base-resolution next generation sequencing approaches and genome wide analyses. Specific classes of short TEs are the predominant targets of mobile sRNA-dependent DNA methylation; classes typically found in gene-rich euchromatic regions. Mobile sRNA-regulated genes were also identified. Mechanistically, we demonstrate that mobile sRNA-dependent non-CG methylation is largely independent of the CMT2/3 RdDM pathway but dependent upon the DRM1/DRM2 RdDM pathway. This is in contrast to non-mobile sRNA-dependent DNA methylation, which predominantly depends upon the CMT2/3 RdDM pathway. These data are complementary to the small RNA sequencing data from Arabidopsis root grafts described in Molnar et al (Science, 2010 May 14;328(5980):872-5).
Project description:Plants reorganize their root architecture to avoid growth into unfavorable regions of the rhizosphere. In a screen based on chimeric repressor gene-silencing technology, we identified the Arabidopsis thaliana GeBP-LIKE 4 (GPL4) transcription factor as an inhibitor of root growth that is induced rapidly in root tips in response to cadmium (Cd). We tested the hypothesis that GPL4 functions in the root avoidance of Cd by analyzing root proliferation in split medium, in which only half of the medium contained toxic concentrations of Cd. The wild-type (WT) plants exhibited root avoidance by inhibiting root growth in the Cd side but increasing root biomass in the control side. By contrast, GPL4-suppression lines exhibited nearly comparable root growth in the Cd and control sides and accumulated more Cd in the shoots than did the WT. GPL4 suppression also altered the root avoidance of toxic concentrations of other essential metals, modulated the expression of many genes related to oxidative stress, and consistently decreased reactive oxygen species concentrations. We suggest that GPL4 inhibits the growth of roots exposed to toxic metals by modulating reactive oxygen species concentrations, thereby allowing roots to colonize noncontaminated regions of the rhizosphere.thereby re-allocating root biomass toward non-contaminated rhizosphere areas and minimizing root exposure to toxic metals.
Project description:Belonging to the Carmovirus family, Turnip crinkle virus (TCV) is a positive-strand RNA virus that can infect Arabidopsis. Most Arabidopsis ecotypes are highly susceptible to TCV, except for the TCV resistant line Di-17 derived from ecotype Dijon. Previous studies showed that many of the stress related genes have changed significantly after TCV infection. Besides the virus-triggered genes, small RNAs also play critical roles in plant defense by triggering either transcriptional and/or post-transcriptional gene silencing. In this study, TCV-infected wildtype Arabidopsis thaliana and dcl1-9 mutant plants were subjected to transcriptome and small RNA analysis to investigate the role of DCL1 in virus defense network.
Project description:Parallel RNA silencing pathways regulate gene expression in plants, either by transcriptional gene silencing via RNA-dependent DNA methylation (RdDM), or by post-transcriptional silencing targeting mRNAs. Both pathways rely on distinct Dicer-like proteins to cleave double-stranded RNA into small-interfering RNAs. Experiments to determine the subcellular localization of Dicer-like proteins in Arabidopsis revealed that DCL4 is predominantly expressed as a transcriptional start site isoform that encodes a cytoplasmic protein. A second, longer DCL4 transcript isoform encodes a nuclear-localization signal and its expression is repressed by DNA methylation. Consequently this isoform is induced when promoter methylation decreases due to infection with a bacterial pathogen or during silique development. Nuclear DCL4 produces unique populations of small RNAs, called DCL4NLS isoform-dependent siRNAs (disiRNAs), which function via a post-transcriptional silencing effector, but whose precursors are generated by the RdDM pathway. Arabidopsis cells can thus respond to genome methylation changes by modulating DCL4 localization, which in turn recruits PTGS factors to reinforce RNA silencing.
Project description:RNA-directed DNA methylation (RdDM) is a small interfering RNA (siRNA)-mediated epigenetic modification that contributes to transposon silencing in plants. RdDM requires a complex transcriptional machinery that includes specialized RNA polymerases, named Pol IV and Pol V, as well as chromatin remodelling proteins, transcription factors, RNA binding proteins, and other plant-specific proteins whose functions are not yet clarified. In Arabidopsis thaliana, DICER-LIKE3 and members of the ARGONAUTE4 group of AROGONAUTE (AGO) proteins are involved, respectively, in generating and using 24-nt siRNAs that trigger methylation and transcriptional gene silencing (TGS) of homologous promoter sequences. AGO proteins act in silencing effector complexes by anchoring the 3â and 5â ends of the guide siRNAs at their N-terminal PAZ domain and MID domain, respectively. In addition, many AGO proteins cleave complementary target RNAs through an endonuclease (âslicerâ) activity in their C-terminal PIWI domain. AGO4 is the main AGO protein implicated in the RdDM pathway. Here we report the identification of the related AGO6 in a forward genetic screen for mutants defective in RdDM and TGS in shoot and root apical meristems in Arabidopsis thaliana. The identification of AGO6, and not AGO4, in our screen is consistent with the primary expression of AGO6 in shoot and root growing points and the preferential association of Pol V with AGO6.
Project description:Belonging to the Carmovirus family, Turnip crinkle virus (TCV) is a positive-strand RNA virus that can infect Arabidopsis. Most Arabidopsis ecotypes are highly susceptible to TCV, except for the TCV resistant line Di-17 derived from ecotype Dijon. Previous studies showed that many of the stress related genes have changed significantly after TCV infection. Besides the virus-triggered genes, small RNAs also play critical roles in plant defense by triggering either transcriptional and/or post-transcriptional gene silencing. In this study, TCV-infected wildtype Arabidopsis thaliana and dcl1-9 mutant plants were subjected to transcriptome and small RNA analysis to investigate the role of DCL1 in virus defense network.