Dataset Information

Arabidopsis lines with modified ascorbate concentrations reveal a link between ascorbate and auxin biosynthesis

ABSTRACT: Ascorbate is the most abundant water-soluble antioxidant in plants and an essential molecule for normal plant development. Although present in all green plants, ascorbate concentrations vary among plant species and tissues. While ascorbate accumulation is a trait of nutritional, and therefore, agronomical interest, the impact of different concentrations on cellular homeostasis remains elusive. To shed light on this question, we compared Arabidopsis (Arabidopsis thaliana) lines with very low (vtc2 mutant, 20% of wild-type (WT) levels), low (vtc4 mutant, 65% of WT levels), and high (vtc2/OE-VTC2, 165% of WT levels) ascorbate concentration in four-week-old rosette leaves. An 80% reduction of ascorbate increased the expression of genes implicated in defense against pathogens but repressed genes associated with abiotic stress responses. Unexpectedly, lines with increased (165% of WT) and decreased (65% of WT) ascorbate levels shared 85% of induced transcription factors and the gene ontology terms associated with their transcriptional programs. We identified TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1), a gene encoding the enzyme that catalyzes the first step of auxin biosynthesis, among the group of genes whose expression was positively correlated with ascorbate content. Using a combination of genetic and pharmacological approaches in fluorescent and histochemical reporter lines for auxin biosynthesis and signaling activity, we revealed that TAA1- and TAA1 RELATED 2 (TAR2)-mediated auxin biosynthesis is necessary for plants to cope with increased ascorbate concentration in a light-dependent manner, revealing a layer of complexity in the regulatory landscape of redox homeostasis.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE296827 | GEO | 2025/05/17

REPOSITORIES: GEO

ACCESS DATA

Dataset's files

Source:

			Action	DRS
		Other

Items per page:

1 - 1 of 1

Similar Datasets

Project description:Ascorbate (vitamin C) is an important antioxidant in leaves with multiple functions in photosynthesis and its levels are tightly regulated by light quality. The majority of work to date has focussed on regulation of ascorbate levels via biosynthesis. However, the pathway of ascorbate degradation, which is localised in the apoplast may additionally play a significant role. The degradative pathway begins with ascorbate oxidation by the enzyme ascorbate oxidase (AO) and hence we have examined the impact of manipulation of ascorbate oxidase activity on the content of ascorbate and the acclimation of photosynthesis to changing light levels. Leaf ascorbate content was highly light dependent in Nicotiana tobaccum being double in high compared with low light conditions. In contrast ascorbate oxidase activity was not altered by changing light levels. Transgenic tobacco lines with reduced or enhanced AO activity exhibited no morphological phenotype and photosynthesis under high light was similarly impaired irrespective of the measured AO activity. However further investigation between AO activity and leaf acclimation to changing light intensity revealed a suite of metabolic and transcriptome changes indicating a role for the apoplastic ascorbate pool in chloroplast to nucleus communication. In all genotypes, transcripts associated with ascorbate synthesis and recycling were less abundant following transition from high to low light. However transcripts associated with glutathione recycling, light harvesting, reaction centre function and the Calvin cycle were all increased in abundance. Following the transition from high to low light increases in leaf threonate, an ascorbate degradation product, were proportional to AO activity. A number of chloroplast synthesised amino acids were significantly increased both during high light and following transfer back to LL for 12 h. Similarly, several primary carbohydrates and TCA intermediates were significantly enhanced following high light treatment. In addition to light effects, AO activity had a significant impact on ï¢-alanine, aspartate and threonine. Intriguingly, a large number of fatty acids were reduced in antisense AO and wild-type plants immediately after high light stress however the content of these compounds were significantly increased in overexpressing sense lines. We conclude that AO mediated turnover plays an important role in adjusting cellular ascorbate content to photosynthetic need in a fluctuating light environment and that light mediated signals rapidly adjust that the apoplastic ascorbate pool.

Project description:This is the single cell model for analysis of hormonal crosstalk in Arabidopsis described in the article: Modelling and experimental analysis of hormonal crosstalk in Arabidopsis. Liu J, Mehdi S, Topping J, Tarkowski P and Lindsey K. Mol Syst Biol. 2010 Jun 8;6:373; PmID: 20531403 , DOI: 10.1038/msb.2010.26 Abstract: An important question in plant biology is how genes influence the crosstalk between hormones to regulate growth. In this study, we model POLARIS (PLS) gene function and crosstalk between auxin, ethylene and cytokinin in Arabidopsis. Experimental evidence suggests that PLS acts on or close to the ethylene receptor ETR1, and a mathematical model describing possible PLS-ethylene pathway interactions is developed, and used to make quantitative predictions about PLS-hormone interactions. Modelling correctly predicts experimental results for the effect of the pls gene mutation on endogenous cytokinin concentration. Modelling also reveals a role for PLS in auxin biosynthesis in addition to a role in auxin transport. The model reproduces available mutants, and with new experimental data provides new insights into how PLS regulates auxin concentration, by controlling the relative contribution of auxin transport and biosynthesis and by integrating auxin, ethylene and cytokinin signalling. Modelling further reveals that a bell-shaped dose-response relationship between endogenous auxin and root length is established via PLS. This combined modelling and experimental analysis provides new insights into the integration of hormonal signals in plants. This model was originally created using Copasi and taken from the supplementary materials of the MSB article. It uses equation 5 for the auxin biosynthesis and was altered to also contain the reactions for ACC, IAA and cytokinine import. Different from the supplementary material, the parameters for the auxin synthesis, v2, are set to k2c = 0.01 uM and k2=0.2 uM_per_sec and for the WT PLS transcription k6=0.3 . To obtain the model described in the first table of the supplementary materials, set k2c=k2=0 and k6=0.9 . For the pls and PLSox mutants, k6 should be set to 0 and 0.45, respectively. This model originates from BioModels Database: A Database of Annotated Published Models. It is copyright (c) 2005-2010 The BioModels Team. For more information see the terms of use . To cite BioModels Database, please use Le Novère N., Bornstein B., Broicher A., Courtot M., Donizelli M., Dharuri H., Li L., Sauro H., Schilstra M., Shapiro B., Snoep J.L., Hucka M. (2006) BioModels Database: A Free, Centralized Database of Curated, Published, Quantitative Kinetic Models of Biochemical and Cellular Systems Nucleic Acids Res., 34: D689-D691.

Project description:We used the flu mutant of Arabidopsis and a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX) to address the interactions between different reactive oxygen species (ROS) signaling pathways. The conditional flu mutant of Arabidopsis accumulates excess protochlorophyllide in the dark within chloroplast membranes that upon illumination acts as a photosensitizer and generates singlet oxygen (1O2). Immediately after the release of singlet oxygen rapid changes in nuclear gene expression occur. Distinct sets of genes were activated that were different from those induced by other reactive oxygen species, superoxide or hydrogen peroxide (H2O2), suggesting that different types of active oxygen species activate distinct signaling pathways. It was not known whether the pathways operate separately or interact with each other. We have addressed this problem by modulating noninvasively the level of H2O2 in plastids by means of a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX, line 14/2 PMID: 15165186). In the flu mutant overexpressing tAPX, the expression of most of the nuclear genes that were rapidly activated after the release of 1O2 was significantly higher in flu plants overexpressing tAPX, whereas in wild-type plants, overexpression of tAPX had only a very minor impact on nuclear gene expression. The results suggest that H2O2 antagonizes the 1O2-mediated signaling of stress responses as seen in the flu mutant. This cross-talk between H2O2- and 1O2-dependent signaling pathways might contribute to the overall stability and robustness of wild-type plants exposed to adverse environmental stress conditions. Experiment Overall Design: Arabidopsis thaliana rosette leaves were harvested after 2 h of reillumination following a 8h dark period for RNA extraction and hybridization on Affymetrix ATH1 microarrays. The entire experiment was performed six times, providing independent biological replicates. For each of the six experiments, all four lines, wild-type, thylakoidal ascorbate peroxidase overexpressor (over tAPX, line 14/2), flu mutant and flu plants overexpressing thylakoidal ascorbate peroxidase were grown for 3 weeks under continuous light at 90 mmol. m-2 . s-1, transferred to the dark for 8 h, and reilluminated for 120 min before the rosette leaves of at least 10 plants per line were harvested. Total RNAs from three separate biological experiments were pooled (= 1 biological rep.) for the preparation of cDNA and the subsequent synthesis of biotin-labeled complementary RNA as recommended by Affymetrix.

Dataset Information

Arabidopsis lines with modified ascorbate concentrations reveal a link between ascorbate and auxin biosynthesis

Dataset's files

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets