Biology subjects

Clement, G.

Publications and source records attributed to Clement, G..

6 recordsLinked to original sources

bioRxiv2022

The Arabidopsis Target of Rapamycin (TOR) kinase regulates ammonium assimilation and glutamine metabolism

In Eukaryotes, Target of Rapamycin (TOR) is a well conserved kinase that controls cell metabolism and growth in response to nutrients and environmental factors. Nitrogen (N) is an essential element for plants and TOR functions as a crucial N and amino acid sensor in animals and yeast. However, the knowledge on the connections between TOR and the overall N metabolism and assimilation in plants is still limited. In this study, we investigate the regulation of TOR in Arabidopsis by the N source as well as the impact of TOR deficiency on N metabolism. Inhibition of TOR globally decreases ammonium uptake while triggering a massive accumulation of amino acids such as Gln, but also of polyamines. Coherently, TOR complex mutants were found to be hypersensitive to Gln. We also show that the glutamine synthetase inhibitor glufosinate abolishes Gln accumulation resulting from TOR inhibition and improves the growth of TOR complex mutants. These results suggest that a high level of Gln contributes to the reduction in plant growth resulting from TOR inhibition. Glutamine synthetase activity was reduced by TOR inhibition while the enzyme amount increased. In conclusion our findings show that the TOR pathway is intimately connected to N metabolism and that a decrease in TOR activity results in a glutamine synthetase-dependent Gln and amino acids accumulation. One sentence summaryThe conserved Target of Rapamycin (TOR) kinase is an important sensor and regulator of the nitrogen metabolism and here we show that inhibiting this kinase affects ammonium uptake and results in Gln accumulation in a glutamine synthetase-dependent manner.

plant biology↗

bioRxiv2022

Arabidopsis hydathodes are sites of intense auxin metabolism and nutrient scavenging

Hydathodes are small organs located on the leaf margins of all vascular plants. They release excess xylem sap through guttation when stomata are closed or when the humidity level is high. Many promoter analyses have suggested other hydathode functions in metabolite transport and auxin metabolism, but experimental demonstration is still lacking. Here, we compared the transcriptomic and metabolomic features of mature Arabidopsis hydathodes to the leaf blade. 1460 differentially-expressed genes were identified revealing that genes related to auxin metabolism, transport, stress, DNA, plant cell wall, RNA or wax were on average more expressed in hydathodes. On the other hand, genes involved in glucosinolate metabolism, sulfation pathway, metal handling or photosynthesis were downregulated in hydathodes. In hydathodes, there are an increased expression of auxin transcriptional regulators and biosynthetic genes, a lower expression of auxin transport genes and a differential expression of genes related to its vacuolar storage that is consistent with increased contents of free and conjugated auxin. We also found that ca. 78% of the total content of 52 xylem sap metabolites were removed from guttation fluid at the hydathode level. Using reverse genetics, we showed that the capture of nitrate and phosphate in the guttation fluid relies on the NRT2.1 and PHT1;4 transporters, respectively. Thus, hydathodes absorb a significant part of xylem sap nutrients, limiting the loss of valuable chemicals during guttation. Our transcriptomic and metabolomic analyses reveal an organ with its own transcriptomic and physiological identity and highlight hydathode biological processes that may impact the whole plant. One sentence summaryTranscriptome and physiological analysis of mature and healthy hydathodes of Arabidopsis demonstrates that those organs are sites of intense auxin metabolism and nutrient scavenging

plant biology↗

bioRxiv2022

The Arabidopsis transcription factor NLP2 regulates early nitrate responses and integrates nitrate assimilation with energy and carbon skeleton supply

Nitrate signaling improves plant growth under limited nitrate availability and, hence, optimal resource use for crop production. Ongoing work has identified several transcriptional regulators of nitrate signaling, including the Arabidopsis thaliana transcription factor NIN-LIKE PROTEIN 7 (NLP7), but additional regulators likely remain to be identified. Here, we characterized Arabidopsis NLP2 as a master upstream transcriptional regulator of early nitrate responses that interacts with NLP7 in vivo and shares key molecular features such as nitrate-dependent nuclear localization, a DNA binding motif, and some target genes with NLP7. Additional genetic, genomic and metabolic approaches revealed a specific role for NLP2 in the nitrate-dependent regulation of carbon and energy-related processes that likely influence plant growth under distinct nitrogen environments. Our findings highlight the complementarity and specificity of NLP2 and NLP7 in orchestrating a multi-tiered nitrate regulatory network that links nitrate assimilation with carbon and energy metabolism for efficient nitrogen use and biomass production. One-sentence summaryNLP2 and NLP7 orchestrate plant responses to nitrate supply and control nitrate- dependent regulation of carbon and energy metabolism.

plant biology↗

bioRxiv2022

Tandem Walk in Simulated Martian Gravity and Visual Environment

Astronauts returning from long-duration spaceflights experience visual-vestibular conflicts that causes motion sickness, perceptions that the environment is moving when it is not, problems with walking, and other functional tasks. To evaluate whether astronauts will have similar decrements associated with visual-vestibular conflicts after they land on Mars following exposure to weightlessness, participants were held by a device that offloads their weight; first entirely (0 G) for 10 minutes, and then partially (0.38 G) or not at all (1 G) for 15 minutes. Tandem (heel-to-toe) walk was used to assess the subjects walking performance. Ten subjects performed 2 trials of 10 steps on a medium-density foam surface. Four conditions were investigated: (a) 1 G in virtual reality (VR); (b) 1 G in VR with a superimposed disorienting optokinetic simulation (VR+DOS); (c) 0.38 G in VR; and (d) 0.38 G in VR+DOS. Tandem walk performance decreased in VR+DOS compared to VR in both 1 G and simulated 0.38 G. Tandem walking performance in VR+DOS was better in 0.38 G compared to 1 G. Tandem walking performance in VR+DOS in 1 G was not significantly different from tandem walking performance after spaceflight or bed rest. The increased tandem walking performance in 0.38 G compared to 1 G was presumably due to an increased cone of stability, allowing larger amplitude of body sway without resulting in a fall. Tandem walking on a compliant foam surface in VR+DOS is a potential analog for simulating postflight dynamic balance deficits in astronauts.

neuroscience↗

bioRxiv2022

Continuous Daily Head and Trunk Acceleration Recording for the Assessment of Bone Stimulation in Astronauts

The acceleration of the head and hip along the x-, y-, and z-axis of 14 healthy subjects was recorded during two sessions of 12 consecutive hours. The magnitude, frequency content, and root mean square of the acceleration signals were used to determine the type of physical activity (sitting, standing, walking, etc.) during normal daily life on Earth. The acceleration signal slope (jerk) was also calculated to assess whether these activities were sufficient to maintain bone mineral density. These measurements indicated that the changes in vertical acceleration experienced by our subjects during normal daily life were presumably sufficient to maintain bone mineral density. However, these changes might not be sufficient for postmenopausal women and astronauts during long-term exposure to weightlessness during spaceflight.

neuroscience↗

bioRxiv2020

Does gravity shape internal representations of space for human 3D perception?

Human 3D perception of visual objects is flawed by distortions, which are influenced by non-visual factors, such as gravitational vestibular signals. Whether gravity acts specifically on the visual system or at a higher, modality-independent, level of information processing remains unknown. To test these modality-specific vs modality-independent hypotheses, we performed experiments comparing visual versus haptic 3D shape perception in normo-gravity and microgravity. The results obtained for upright and supine posture in 1g show that visual and haptic perceptual anisotropies are systematically in opposing ego-centered, but not gravity-centered, directions suggesting they share a common origin. On the other hand, microgravity significantly modulates both visual and haptic perceptual distortion in the same direction. Overall, our results show a clear link between the visual and haptic perceptual distortions and demonstrate a role of gravity-related signals on a modality-independent internal representation of 3D space used to interpret incoming sensory inputs.

neuroscience↗