Compound-Specific 14N/15N Analysis of Amino Acid Trimethylsilylated Derivatives from Plant Seed Proteins

Isotopic analyses of plant samples are now of considerable importance for food certification and plant physiology. In fact, the natural nitrogen isotope composition (δ15N) is extremely useful to examine metabolic pathways of N nutrition involving isotope fractionations. However, δ15N analysis of amino acids is not straightforward and involves specific derivatization procedures to yield volatile derivatives that can be analysed by gas chromatography coupled to isotope ratio mass spectrometry (GC-C-IRMS). Derivatizations other than trimethylsilylation are commonly used since they are believed to be more reliable and accurate. Their major drawback is that they are not associated with metabolite databases allowing identification of derivatives and by-products. Here, we revisit the potential of trimethylsilylated derivatives via concurrent analysis of δ15N and exact mass GC-MS of plant seed protein samples, allowing facile identification of derivatives using a database used for metabolomics. When multiple silylated derivatives of several amino acids are accounted for, there is a good agreement between theoretical and observed N mole fractions, and δ15N values are satisfactory, with little fractionation during derivatization. Overall, this technique may be suitable for compound-specific δ15N analysis, with pros and cons

Experimental Evidence for Seed Metabolic Allometry in Barrel Medic (Medicago truncatula Gaertn.)

International audienceSeed size is often considered to be an important trait for seed quality, i.e., vigour and germination performance. It is believed that seed size reflects the quantity of reserve material and thus the C and N sources available for post-germinative processes. However, mechanisms linking seed size and quality are poorly documented. In particular, specific metabolic changes when seed size varies are not well-known. To gain insight into this aspect, we examined seed size and composition across different accessions of barrel medic (Medicago truncatula Gaertn.) from the genetic core collection. We conducted multi-elemental analyses and isotope measurements, as well as exact mass GC–MS metabolomics. There was a systematic increase in N content (+0.17% N mg−1) and a decrease in H content (–0.14% H mg−1) with seed size, reflecting lower lipid and higher S-poor protein quantity. There was also a decrease in 2H natural abundance (δ2H), due to the lower prevalence of 2H-enriched lipid hydrogen atoms that underwent isotopic exchange with water during seed development. Metabolomics showed that seed size correlates with free amino acid and hexoses content, and anticorrelates with amino acid degradation products, disaccharides, malic acid and free fatty acids. All accessions followed the same trend, with insignificant differences in metabolic properties between them. Our results show that there is no general, proportional increase in metabolite pools with seed size. Seed size appears to be determined by metabolic balance (between sugar and amino acid degradation vs. utilisation for storage), which is in turn likely determined by phloem source metabolite delivery during seed development

Mitochondrial Complex I Disruption Causes Broad Reorchestration of Plant Lipidome Including Chloroplast Lipids

Mitochondrial complex I (CI) plays a crucial role in oxidising NADH generated by the metabolism (including photorespiration) and thereby participates in the mitochondrial electron transfer chain feeding oxidative phosphorylation that generates ATP. However, CI mutations are not lethal in plants and cause moderate phenotypes, and therefore CI mutants are instrumental to examine consequences of mitochondrial homeostasis disturbance on plant cell metabolisms and signalling. To date, the consequences of CI disruption on the lipidome have not been examined. Yet, in principle, mitochondrial dysfunction should impact on lipid synthesis through chloroplasts (via changes in photorespiration, redox homeostasis, and N metabolism) and the endoplasmic reticulum (ER) (via perturbed mitochondrion–ER crosstalk). Here, we took advantage of lipidomics technology (by LC-MS), phospholipid quantitation by 31P-NMR, and total lipid quantitation to assess the impact of CI disruption on leaf, pollen, and seed lipids using three well-characterised CI mutants: CMSII in N. sylvestris and both ndufs4 and ndufs8 in Arabidopsis. Our results show multiple changes in cellular lipids, including galactolipids (chloroplastic), sphingolipids, and ceramides (synthesised by ER), suggesting that mitochondrial homeostasis is essential for the regulation of whole cellular lipidome via specific signalling pathways. In particular, the observed modifications in phospholipid and sphingolipid/ceramide molecular species suggest that CI activity controls phosphatidic acid-mediated signalling

Mitochondrial Complex I Disruption Causes Broad Reorchestration of Plant Lipidome Including Chloroplast Lipids

International audienceMitochondrial complex I (CI) plays a crucial role in oxidising NADH generated by the metabolism (including photorespiration) and thereby participates in the mitochondrial electron transfer chain feeding oxidative phosphorylation that generates ATP. However, CI mutations are not lethal in plants and cause moderate phenotypes, and therefore CI mutants are instrumental to examine consequences of mitochondrial homeostasis disturbance on plant cell metabolisms and signalling. To date, the consequences of CI disruption on the lipidome have not been examined. Yet, in principle, mitochondrial dysfunction should impact on lipid synthesis through chloroplasts (via changes in photorespiration, redox homeostasis, and N metabolism) and the endoplasmic reticulum (ER) (via perturbed mitochondrion–ER crosstalk). Here, we took advantage of lipidomics technology (by LC-MS), phospholipid quantitation by 31P-NMR, and total lipid quantitation to assess the impact of CI disruption on leaf, pollen, and seed lipids using three well-characterised CI mutants: CMSII in N. sylvestris and both ndufs4 and ndufs8 in Arabidopsis. Our results show multiple changes in cellular lipids, including galactolipids (chloroplastic), sphingolipids, and ceramides (synthesised by ER), suggesting that mitochondrial homeostasis is essential for the regulation of whole cellular lipidome via specific signalling pathways. In particular, the observed modifications in phospholipid and sphingolipid/ceramide molecular species suggest that CI activity controls phosphatidic acid-mediated signalling

Mitochondrial Complex I Disruption Causes Broad Reorchestration of Plant Lipidome Including Chloroplast Lipids

International audienceMitochondrial complex I (CI) plays a crucial role in oxidising NADH generated by the metabolism (including photorespiration) and thereby participates in the mitochondrial electron transfer chain feeding oxidative phosphorylation that generates ATP. However, CI mutations are not lethal in plants and cause moderate phenotypes, and therefore CI mutants are instrumental to examine consequences of mitochondrial homeostasis disturbance on plant cell metabolisms and signalling. To date, the consequences of CI disruption on the lipidome have not been examined. Yet, in principle, mitochondrial dysfunction should impact on lipid synthesis through chloroplasts (via changes in photorespiration, redox homeostasis, and N metabolism) and the endoplasmic reticulum (ER) (via perturbed mitochondrion–ER crosstalk). Here, we took advantage of lipidomics technology (by LC-MS), phospholipid quantitation by 31P-NMR, and total lipid quantitation to assess the impact of CI disruption on leaf, pollen, and seed lipids using three well-characterised CI mutants: CMSII in N. sylvestris and both ndufs4 and ndufs8 in Arabidopsis. Our results show multiple changes in cellular lipids, including galactolipids (chloroplastic), sphingolipids, and ceramides (synthesised by ER), suggesting that mitochondrial homeostasis is essential for the regulation of whole cellular lipidome via specific signalling pathways. In particular, the observed modifications in phospholipid and sphingolipid/ceramide molecular species suggest that CI activity controls phosphatidic acid-mediated signalling

Pivotal roles of environmental sensing and signaling mechanisms in plant responses to climate change

International audienceClimate change reshapes the physiology and development of organisms through phenotypic plasticity, epigenetic modifications and genetic adaptation. Under evolutionary pressures of the sessile lifestyle, plants possess efficient systems of phenotypic plasticity and acclimation to environmental conditions. Molecular analysis, especially through omics approaches, of these primary lines of environmental adjustment in the context of climate change has revealed the underlying biochemical and physiological mechanisms, thus characterising the links between phenotypic plasticity and climate change responses. Efficiency of adaptive plasticity under climate change indeed depends on the realization of such biochemical and physiological mechanisms, but the importance of sensing and signaling mechanisms that can integrate perception of environmental cues and transduction into physiological responses are often overlooked. Recent progress opens the possibility of considering plant phenotypic plasticity and responses to climate change through the perspective of environmental sensing and signaling. This review aims to analyse present knowledge on plant sensing and signaling mechanisms and discuss how their structural and functional characteristics lead to resilience or hypersensitivity under conditions of climate change. Plant cells are endowed with arrays of environmental and stress sensors and with internal signals that act as molecular integrators of the multiple constraints of climate change, thus giving rise to potential mechanisms of climate change sensing. Moreover, mechanisms of stress-related information propagation lead to stress memory and acquired stress tolerance that could withstand different scenarios of modifications of stress frequency and intensity. However, optimal functioning of existing sensors, optimal integration of additive constraints and signals, or memory processes can be hampered by conflicting interferences between novel combinations and novel changes of intensity and duration of climate-change-related factors. Analysis of these contrasted situations emphasises the need for future research on the diversity and robustness of plant signaling mechanisms under climate change conditions. This article is protected by copyright. All rights reserved

Grain carbon isotope composition is a marker for allocation and harvest index in wheat

The natural C-13 abundance (delta C-13) in plant leaves has been used for decades with great success in agronomy to monitor water-use efficiency and select modern cultivars adapted to dry conditions. However, in wheat, it is also important to find genotypes with high carbon allocation to spikes and grains, and thus with a high harvest index (HI) and/or low carbon losses via respiration. Finding isotope-based markers of carbon partitioning to grains would be extremely useful since isotope analyses are inexpensive and can be performed routinely at high throughput. Here, we took the advantage of a set of field trials made of more than 600 plots with several wheat cultivars and measured agronomic parameters as well as delta C-13 values in leaves and grains. We find a linear relationship between the apparent isotope discrimination between leaves and grain (denoted as Delta delta(corr)), and the respiration use efficiency-to-HI ratio. It means that overall, efficient carbon allocation to grains is associated with a small isotopic difference between leaves and grains. This effect is explained by postphotosynthetic isotope fractionations, and we show that this can be modelled by equations describing the carbon isotope composition in grains along the wheat growth cycle. Our results show that C-13 natural abundance in grains could be useful to find genotypes with better carbon allocation properties and assist current wheat breeding technologies

Grain carbon isotope composition is a marker for allocation and harvest index in wheat

International audienceThe natural C-13 abundance (delta C-13) in plant leaves has been used for decades with great success in agronomy to monitor water-use efficiency and select modern cultivars adapted to dry conditions. However, in wheat, it is also important to find genotypes with high carbon allocation to spikes and grains, and thus with a high harvest index (HI) and/or low carbon losses via respiration. Finding isotope-based markers of carbon partitioning to grains would be extremely useful since isotope analyses are inexpensive and can be performed routinely at high throughput. Here, we took the advantage of a set of field trials made of more than 600 plots with several wheat cultivars and measured agronomic parameters as well as delta C-13 values in leaves and grains. We find a linear relationship between the apparent isotope discrimination between leaves and grain (denoted as Delta delta(corr)), and the respiration use efficiency-to-HI ratio. It means that overall, efficient carbon allocation to grains is associated with a small isotopic difference between leaves and grains. This effect is explained by postphotosynthetic isotope fractionations, and we show that this can be modelled by equations describing the carbon isotope composition in grains along the wheat growth cycle. Our results show that C-13 natural abundance in grains could be useful to find genotypes with better carbon allocation properties and assist current wheat breeding technologies

Cardiac overexpression of PDE4B blunts β-adrenergic response and maladaptive remodeling in heart failure

International audienceBackground The cAMP-hydrolyzing phosphodiesterase 4B (PDE4B) is a key negative regulator of cardiac β-adrenergic (β-AR) stimulation. PDE4B deficiency leads to abnormal Ca2+ handling and PDE4B is decreased in pressure overload hypertrophy, suggesting that increasing PDE4B in the heart is beneficial in heart failure (HF). Methods: We measured PDE4B expression in human cardiac tissues, developed two transgenic mouse lines with cardiomyocyte-specific overexpression of PDE4B (PDE4B-TG), and an adeno-associated virus serotype 9 encoding PDE4B (AAV9-PDE4B). Myocardial structure and function were evaluated by echocardiography, ECG, and in Langendorff-perfused hearts. Cyclic AMP and PKA activity were monitored by Förster resonance energy transfer, ICa,L by whole cell patch-clamp, and cardiomyocyte shortening and Ca2+ transients with an Ionoptix® system. HF was induced by 2 weeks infusion of isoproterenol (Iso) or transverse aortic constriction (TAC). Cardiac remodeling was evaluated by serial echocardiography, morphometric analysis and histology. Results: PDE4B protein was decreased in human failing hearts. The first PDE4B-TG mouse line (TG15) had a ~15-fold increase in cardiac cAMP-PDE activity and a ~30% decrease in cAMP content and fractional shortening associated with a mild cardiac hypertrophy that resorbed with age. Basal ex vivo myocardial function was unchanged, but β-AR stimulation of cardiac inotropy, cAMP, PKA, ICa,L, Ca2+ transients and cell contraction were blunted. Endurance capacity and life expectancy were normal. Moreover, these mice were protected from systolic dysfunction, hypertrophy, lung congestion and fibrosis induced by chronic Iso treatment. In the second transgenic mouse line (TG50), markedly higher PDE4B overexpression, resulting in a ~50-fold increase in cardiac cAMP-PDE activity caused a ~50% decrease in fractional shortening, hypertrophy, dilatation and premature death. In contrast, mice injected with AAV9-PDE4B (1012 viral particles/mouse) had a ~50% increase in cardiac cAMP-PDE activity which did not modify basal cardiac function but efficiently prevented systolic dysfunction, apoptosis and fibrosis, while attenuating hypertrophy induced by chronic Iso infusion. Similarly, AAV9-PDE4B slowed contractile deterioration, attenuated hypertrophy and lung congestion and prevented apoptosis and fibrotic remodeling in TAC. Conclusions: Our results indicate that a moderate increase in PDE4B is cardioprotective and suggest that cardiac gene therapy with PDE4B might constitute a new promising approach to treat HF