Photoperiod affects the phenotype of mitochondrial complex I mutants

Plant mutants for genes encoding subunits of mitochondrial Complex I (CI, NADH:ubiquinone oxidoreductase), the first enzyme of the respiratory chain, display various phenotypes depending on growth conditions. Here, we examined the impact of photoperiod, a major environmental factor controlling plant development, on two Arabidopsis thaliana CI mutants: a new insertion mutant interrupted in both ndufs8.1 and ndufs8.2 genes encoding the NDUFS8 subunit, and the previously characterized ndufs4 CI mutant. In long day (LD) condition, both ndufs8.1 and ndufs8.2 single mutants were indistinguishable from Col-0 at phenotypic and biochemical levels, whereas the ndufs8.1 ndufs8.2 double mutant was devoid of detectable holo-CI assembly/activity, showed higher AOX content/activity and displayed a growth-retardation phenotype similar to that of the ndufs4 mutant. Although growth was more affected in ndufs4 than ndufs8.1 ndufs8.2 under short day (SD) condition, both mutants displayed a similar impairment of growth acceleration after transfer to LD as compared to the WT. Untargeted and targeted metabolomics showed that overall metabolism was less responsive to the SD-to-LD transition in mutants than in the WT. The typical LD acclimation of carbon, nitrogen-assimilation and redox-related parameters was not observed in ndufs8.1 ndufs8. Similarly, NAD(H) content, that was higher in SD condition in both mutants than in Col-0, did not adjust under LD. We propose that altered redox homeostasis and NAD(H) content/redox state control the phenotype of Complex I mutants and photoperiod acclimation in Arabidopsis

More to NAD(+) than meets the eye: A regulator of metabolic pools and gene expression in Arabidopsis

UMR BFP - Equipe MétabolismeInternational audienceSince its discovery more than a century ago, nicotinamide adenine dinucleotide (NAD+) is recognised as a fascinating cornerstone of cellular metabolism. This ubiquitous energy cofactor plays vital roles in metabolic pathways and regulatory processes, a fact emphasised by the essentiality of a balanced NAD+ metabolism for normal plant growth and development. Research on the role of NAD in plants has been predominantly carried out in the model plant Arabidopsis thaliana (Arabidopsis) with emphasis on the redox properties and cellular signalling functions of the metabolite. This review examines the current state of knowledge concerning how NAD can regulate both metabolic pools and gene expression in Arabidopsis. Particular focus is placed on recent studies highlighting the complexity of metabolic regulations involving NAD, more particularly in the mitochondrial compartment, and of signalling roles with respect to interactions with environmental fluctuations most specifically those involving plant immunity

Molecular analysis and control of cysteine biosynthesis: integration of nitrogen and sulphur metabolism

Since cysteine is the first committed molecule in plant metabolism containing both sulphur and nitrogen, the regulation of its biosynthesis is critically important. Cysteine itself is required for the production of an abundance of key metabolites in diverse pathways. Plants alter their metabolism to compensate for sulphur and nitrogen deficiencies as best as they can, but limitations in either nutrient not only curb a plant's ability to synthesize cysteine, but also restrict protein synthesis. Nutrients such as nitrate and sulphate (and carbon) act as signals; they trigger molecular mechanisms that modify biosynthetic pathways and thereby have a profound impact on metabolite fluxes. Cysteine biosynthesis is modified by regulators acting at the site of uptake and throughout the plant system. Recent data point to the existence of nutrient-specific signal transduction pathways that relay information about external and internal nutrient concentrations, resulting in alterations to cysteine biosynthesis. Progress in this field has led to the cloning of genes that play pivotal roles in nutrient-induced changes in cysteine formation

NAD acts as an integral regulator of multiple defense layers

Pyridine nucleotides, such as nicotinamide adenine dinucleotide (NAD), are crucial redox carriers and have emerged as important signaling molecules in stress responses. Previously, we have demonstrated in Arabidopsis thaliana (Arabidopsis) that the inducible NAD-overproducing nadC lines are more resistant to an avirulent strain of Pseudomonas syringae pv. tomato (Pst-AvrRpm1), which was associated with salicylic acid-dependent defense. Here, we have further characterized the NAD-dependent immune response in Arabidopsis. Quinolinate-induced stimulation of intracellular NAD in transgenic nadC plants enhanced resistance against a diverse range of (a)virulent pathogens, including Pst-AvrRpt2, Dickeya dadantii and Botrytis cinerea. Characterization of the redox status demonstrated that elevated NAD levels induce reactive oxygen species (ROS) production and expression of redox marker genes of the cytosol and mitochondrion. Using pharmacological and reverse genetics approaches, we show that NAD-induced ROS production functions independently of NADPH oxidase activity and light metabolism but depends on mitochondrial respiration which was increased at higher NAD. We further demonstrate that NAD primes pathogen-induced callose deposition and cell death. Mass spectrometry analysis reveals that NAD simultaneously induces different defense hormones and that the NAD-induced metabolic profiles are similar to that of defense-expressing plants after treatment with pathogen-associated molecular patterns (PAMPs). We thus conclude that NAD triggers metabolic profiles rather similar to that of PAMPs and discuss how signaling crosstalk between defense hormones, ROS and NAD explains the observed resistance to pathogens

Towards dissecting nutrient metabolism in plants: a systems biology case study on sulphur metabolism

A genomics analysis on sulphur metabolism has been conducted at the level of transcriptomics and metabolomics. The analysis of these data after applying bioinformatic tools is to reveal novel findings. The findings are discussed and the knowledge obtained from comparable analyses on sulphur metabolism and other plant nutrient genomic studies is reviewed. The analysis of the response of the transcriptome and metabolome to sulphur deprivation in the growth medium provides a tool set for the analysis of comparable genomics studies of other nutrients. The goal of this 'sulphobolomics' (i.e. sulphur genomics and metabolome analysis) approach, and of other investigations, is to describe in a holistic way the biochemical, molecular, and physiological response of a plant to nutrient starvation, here sulphate, or, more generally, to alterations and imbalances in nutrient availability. Eventually, this analysis will provide a case study for a systems biology approach

Towards dissecting nutrient metabolism in plants: a systems biology case study on sulphur metabolism

A genomics analysis on sulphur metabolism has been conducted at the level of transcriptomics and metabolomics. The analysis of these data after applying bioinformatic tools is to reveal novel findings. The findings are discussed and the knowledge obtained from comparable analyses on sulphur metabolism and other plant nutrient genomic studies is reviewed. The analysis of the response of the transcriptome and metabolome to sulphur deprivation in the growth medium provides a tool set for the analysis of comparable genomics studies of other nutrients. The goal of this 'sulphobolomics' (i.e. sulphur genomics and metabolome analysis) approach, and of other investigations, is to describe in a holistic way the biochemical, molecular, and physiological response of a plant to nutrient starvation, here sulphate, or, more generally, to alterations and imbalances in nutrient availability. Eventually, this analysis will provide a case study for a systems biology approach

Effect of sulfur availability on the integrity of amino acid biosynthesis in plants

Amino acid levels in plants are regulated by a complex interplay of regulatory circuits at the level of enzyme activities and gene expression. Despite the diversity of precursors involved in amino acid biosynthesis as providing the carbon backbones, the amino groups and, for the amino acids methionine and cysteine, the sulfhydryl group and despite the involvement of amino acids as substrates in various downstream metabolic processes, the plant usually manages to provide relatively constant levels of all amino acids. Here we collate data on how amino acid homeostasis is shifted upon depletion of one of the major biosynthetic constituents, i.e., sulfur. Arabidopsis thaliana seedlings exposed to sulfate starvation respond with a set of adaptation processes to achieve a new balance of amino acid metabolism. First, metabolites containing reduced sulfur (cysteine, glutathione, S-adenosylmethionine) are reduced leading to a number of downstream effects. Second, the relative excess accumulation of N over S triggers processes to dump nitrogen in asparagine, glutamine and further N-rich compounds like ureides. Third, the depletion of glutathione affects the redox and stress response system of the glutathione-ascorbate cycle. Thus, biosynthesis of aromatic compounds is triggered to compensate for this loss, leading to an increased flux and accumulation of aromatic amino acids, especially tryptophan. Despite sulfate starvation, the homeostasis is kept, though shifted to a new state. This adaptation process keeps the plant viable even under an adverse nutritional status

From intracellular bacteria to differentiated bacteroids : transcriptome and metabolome analysis in aeschynomene nodules using the Bradyrhizobium sp. Strain ORS285 bclA mutant

Soil bacteria called rhizobia trigger the formation of root nodules on legume plants. The rhizobia infect these symbiotic organs and adopt an intracellular lifestyle within the nodule cells, where they differentiate into nitrogen-fixing bacteroids. Several legume lineages force their symbionts into an extreme cellular differentiation, comprising cell enlargement and genome endoreduplication. The antimicrobial peptide transporter BclA is a major determinant of this process in Bradyrhizobium sp. strain ORS285, a symbiont of Aeschynomene spp. In the absence of BclA, the bacteria proceed until the intracellular infection of nodule cells, but they cannot differentiate into enlarged polyploid and functional bacteroids. Thus, the bclA nodule bacteria constitute an intermediate stage between the free-living soil bacteria and the nitrogen-fixing bacteroids. Metabolomics on whole nodules of Aeschynomene afraspera and Aeschynomene indica infected with the wild type or the bclA mutant revealed 47 metabolites that differentially accumulated concomitantly with bacteroid differentiation. Bacterial transcriptome analysis of these nodules demonstrated that the intracellular settling of the rhizobia in the symbiotic nodule cells is accompanied by a first transcriptome switch involving several hundred upregulated and downregulated genes and a second switch accompanying the bacteroid differentiation, involving fewer genes but ones that are expressed to extremely elevated levels. The transcriptomes further suggested a dynamic role for oxygen and redox regulation of gene expression during nodule formation and a nonsymbiotic function of BclA. Together, our data uncover the metabolic and gene expression changes that accompany the transition from intracellular bacteria into differentiated nitrogen-fixing bacteroids. IMPORTANCE Legume-rhizobium symbiosis is a major ecological process, fueling the biogeochemical nitrogen cycle with reduced nitrogen. It also represents a promising strategy to reduce the use of chemical nitrogen fertilizers in agriculture, thereby improving its sustainability. This interaction leads to the intracellular accommodation of rhizobia within plant cells of symbiotic organs, where they differentiate into nitrogen-fixing bacteroids. In specific legume clades, this differentiation process requires the bacterial transporter BclA to counteract antimicrobial peptides produced by the host. Transcriptome analysis of Bradyrhizobium wild-type and bclA mutant bacteria in culture and in symbiosis with Aeschynomene host plants dissected the bacterial transcriptional response in distinct phases and highlighted functions of the transporter in the free-living stage of the bacterial life cycle

The aspartic acid metabolic pathway, an exciting and essential pathway in plants.

Aspartate is the common precursor of the essential amino acids lysine, threonine, methionine and isoleucine in higher plants. In addition, aspartate may also be converted to asparagine, in a potentially competing reaction. The latest information on the properties of the enzymes involved in the pathways and the genes that encode them is described. An understanding of the overall regulatory control of the flux through the pathways is undisputedly of great interest, since the nutritive value of all cereal and legume crops is reduced due to low concentrations of at least one of the aspartate-derived amino acids. We have reviewed the recent literature and discussed in this paper possible methods by which the concentrations of the limiting amino acids may be increased in the seeds