Project description:Auxin is a key phytohormone regulating central processes in plants that include embryo development, lateral root growth and flower maturation among others. Auxin is sensed by a set of F-Box proteins of the TIR1/AFB3 family triggering auxin dependent responses by a pathway that involves an interplay between the Aux/IAA transcription repressors and the ARF transcription factors. We have previously shown that the AFB3 auxin receptor has a specific role in coordinating primary and lateral root growth to external and internal nitrate availability (Vidal et al., 2010). In this work, we used an integrated genomics, bioinformatics and molecular genetics approach to dissect regulatory networks acting downstream AFB3 that are activated by a transient nitrate treatment in Arabidopsis roots. Our systems approach unraveled key components of the AFB3 regulatory network leading to changes in lateral root growth in response to nitrate. Arabidopsis seedlings of the Ws and afb3-1 genotypes were grown on hydroponic medium containing 1X MS salts without Nitrogen, supplemented with 0.5 mM ammonium succinate as Nitrogen source and 3 mM sucrose on a Percival chamber under a photoperiod of 16 hours of light (100 μE/m2/sec) and 8 hours of dark at 22°C for 14 days. The plants were treated at the onset of the light cycle with 5 mM KNO3 or 5 mM KCl as control for 2 hours. Whole roots were cut from seedlings and frozen on liquid Nitrogen. Total RNA was extracted using the TriZol reagent. 3 independent biological replicates were performed.
Project description:Plants modulate the efficiency of root nitrogen (N) acquisition in response to shoot N demand. However, molecular components directly involved in this shoot-to-root communication remain to be identified. Here, we show that phloem-mobile CEPD-like 2 (CEPDL2) polypeptide is upregulated in the leaf vasculature in response to decreased shoot N status and, after translocation to the roots, promotes high-affinity uptake and root-to-shoot transport of nitrate by activating nitrate transporter genes such as NRT2.1, NRT3.1 and NRT1.5. Loss of CEPDL2 decreases nitrate uptake and root-to-shoot transport activity in roots, leading to a reduction in shoot nitrate content and plant biomass. CEPDL2 contributes to N acquisition cooperatively with CEPD1 and CEPD2 that mediate root N status, and their complete loss severely impairs N homeostasis in plants. Reciprocal grafting analysis provided conclusive evidence that the shoot CEPDL2/CEPD genotype defines the root high-affinity uptake activity of nitrate. Our results indicate that plants integrate shoot N status and root N status in leaves and systemically regulate the efficiency of root N acquisition.
Project description:Arabidopsis Affymetrix ATH1 GeneChips were used to compare the mRNA profiles of root tissues of the grf1/grf2/grf3 triple mutant and transgenic plants overexpressing miR396-resistant variants of GRF1 (P35S:rGRF1) or GRF3 (P35S:rGRF3) with those of the corresponding wild-type (Col-0 or WS). Wild-type (Arabidopsis thaliana ecotypes Col-0 and Ws), the triple mutant grf1/grf2/grf3, and transgenic plants overexpressing rGRF1 or rGRF3 were grown in vertical culture dishes on modified Knop’s medium for 2 weeks and then root tissues were collected for RNA extraction. ****[PLEXdb(http://www.plexdb.org) has submitted this series at GEO on behalf of the original contributor, Tarek Hewezi. The equivalent experiment is AT109 at PLEXdb.]
Project description:In higher plants, NAD synthesis starts with the oxidation of aspartate. This oxidation is catalyzed by aspartate oxidase (AO) encoded by a nitrate-inducible gene. To assess the effects of this upregulation of AO gene in response to a nitrate supply, a transgenic line was generated by introduction of AO gene under the control of a mutated AO promoter into the ao knockout mutant. Since, unlike the wild-type AO promoter, this mutated AO promoter was not activated by a nitrate supply, gene expression in this transgenic line was compared with that in another transgenic line that was generated by introduction of AO gene under the regulation of the wild-type AO promoter into the ao knockout mutant. Changes in gene expression in response to a nitrate supply were analyzed in these transgenic lines.
Project description:As multicellular organisms, plants must integrate responses to environmental cues across different cell types and also over time. Nitrate is the major source of available Nitrogen for plants, and a limiting factor for plant growth and productivity. Plant root s are highly impacted by nitrate availability, modifying their architecture to optimize nitrate uptake from soils. In order to understand how this functional response is dynamically orchestrated across different cell types of the root, space and time must be addressed within the same experimental setup. We performed a transcriptomic analysis in five major root cell types of Arabidopsis plants in response to nitrate treatments considering short and long time exposure to this macronutrient. We found nitrate treatment triggers a dynamic reprogramming of root cell gene expression that follows a spatial pattern over time consistent with an early regulation of nitrate transport and assimilation in external layers of the root and a later regulation of hormonal and developmental processes in more internal layers of the root.
Project description:Plants aquire nitrogen from the soil, most commonly in the form of either nitrate or ammonium. Unlike ammonium, nitrate must be reduced (with NADH and ferredoxin as electron donors) prior to assimilation. Thus, nitrate nutrition imposes a substantially greater energetic cost than ammonium nutrition. Our goal was to compare the transcriptomes of nitrate-supplied and ammonium-supplied plants, with a particular interest in characterizing the differences in redox metabolism elicited by different forms of inorganic nitrogen. We used microarrays to compare the short-term transcriptional response to either nitrogen supply or ammonium supply in Arabidopsis roots. Genes upregulated or downregulated by nitrate only, ammonium only, or both ammonium and nitrate were identified and analyzed. Arabidopsis thaliana (Col-0) plants were grown hydroponically until they reached growth stage 5.10. They were then transferred to a nitrogen-free medium for 26 hr and then supplied with 1 mM nitrate or 1 mM ammonium. RNA isolation (and subsequent microarray analysis) was performed on root tissue isolated just before nitrogen supply (time 0) and at 1.5 hr and 8 hr after nitrogen supply (1.5 hr nitrate, 8 hr nitrate, 1.5 hr ammonium, 8 hr ammonium).
Project description:Nitrate and other nitrogen metabolites can act as signals that regulate global gene expression in plants. Adaptive changes in plant morphology and physiology triggered by changes in nitrate availability are partly explained by these changes in gene expression. Despite several genome-wide efforts to identify nitrate-regulated genes, no comprehensive study of the Arabidopsis root transcriptome under contrasting nitrate conditions has been carried out. In this work, we employed the Illumina high throughput sequencing technology to perform an integrated analysis of the poly-A+ enriched and the small RNA fractions of the Arabidopsis thaliana root transcriptome in response to nitrate treatments. Our sequencing strategy identified new nitrate-regulated genes including 40 genes not represented in the ATH1 Affymetrix GeneChip, a novel nitrate-responsive antisense transcript and a new nitrate responsive miRNA/TARGET module consisting of a novel microRNA, miR5640 and its target, AtPPC3. This nitrate-responsive miRNA/target module might be involved in controlling carbon flux to assimilate nitrate into amino acids, suggesting that microRNAs can have both developmental and metabolic functions in the nitrate response of Arabidopsis roots.
Project description:gnp3-b4_nitrogen_starvation - nitrogen starvation and re-supply - What are the transcriptomic short- and long-term plant responses to nitrogen starvation and nitrogen re-supply? - WS Arabidopsis ecotype were grown on 6mM nitrate as sole nitrogen source during 35 days under short days . At T0, plants were then starved for nitrate for 10 days and root and shoot samples were harvested separately 2 and 10 days after treatment (T2, T10). Then, nitrate (6 mM) was re-supplied for 1 and 24 hours (T+1, T+24). Keywords: time course