Apyrases belong to the ATPase family of enzymes that hydrolyze phosphoanhydride bonds of nucleoside tri- and di-phosphates. These enzymes differ markedly from other phosphohydrolases due to their high specific activity, broad divalent cation requirement, broad nucleotide substrate specificity, and insensitivity to various inhibitors. In the past 30 years, apyrases have been frequently studied in mammals. In comparison, research of apyrases in plants has received little attention, despite the growth of plants being closely related to the apyrases. In this review, we summarize the research of the apyrases in Arabidopsis thaliana and point to the possible future directions of research. Apyrases have seven members found in Arabidopsis thaliana, each with different properties and functions. Currently, the characterization and functions of AtAPY1 and AtAPY2 have been reported, though, to the best of our knowledge, the other apyrase members (AtAPY3 to 7) have not yet been sufficiently described. In this review, we also summarize the progress being made and the difficulties encountered in apyrase research in Arabidopsis thaliana.

La photorespiration est un processus essential chez tous les organismes photosynthétiques. Elle est déclenchée par l’activité oxygénase de la Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (RuBisCO) menant à la production d’une molécule de 3-phosphoglycerate and une molécule de 2-phosphoglycolate (2PG). Le 2PG est toxique et sera recyclé par la photorespiration qui implique huit principales enzymes et prend place dans les chloroplastes, les peroxysomes, les mitochondries et le cytosol. Bien que la photorespiration aboutisse à une efficacité réduite de l’assimilation du CO₂ photosynthétique et soit considérée comme un processus inutile, le phénotype de croissance des mutants d’enzymes photorespiratoires (croissance réduite, chlorose) reflète l’importance de ce processus dans la croissance et le développement normal car il interagit avec plusieurs voies métaboliques primaires. Les données actuelles montrent que sept des huit principales enzymes photorespiratoires pourraient être phosphorylées et qu’ainsi la phosphorylation pourrait être un élément régulateur essentiel du cycle photorespiratoire. Afin de mieux comprendre la régulation du cycle photorespiratoire, nous avons étudié l’effet d’une phosphorylation/ absence de phosphorylation sur la sérine hydroxyméthyltransférase 1 mitochondriale (SHMT1) et de l’hydroxypyruvate réductase peroxisomale en utilisant des versions de ces enzymes mimant une phosphorylation (sérine ou la thréonine mutée en acide aspartique) ou une absence de phosphoryaltion (sérine ou thréonine mutée en alanine).Deux sites sont phosphorylés chez HPR1: S229 et T335. La mutation de ces sites montre que seule la version mimant une phosphorylation sur le site T335 (HPR1 T335D) entraîne une activité réduite de la protéine recombinante HPR1. Ce résultat a été confirmé in vivo puisque le mutant Arabidopsis hpr1 exprimant HPR1 T33D était incapable de totalement complémenter le phénotype photorespiratoire du mutant hpr1.Par complémentation du mutant d’Arabidopsis shm1-1 par une forme sauvage de SHMT1, d’une version mimant (S31D) ou non (S31A) une phosphorylation, les résultats ont montré que toutes les formes de SHMT1 pouvaient presque totalement complémenter le phénotype de croissance de shm1-1. Cependant, chaque ligne transgénique n'avait que 50% de l'activité de SHMT normale. En réponse à un stress dû au sel ou à la sécheresse, les lignées Compl-S31D ont montré un déficit de croissance plus accentué que les autres lignées transgéniques. Cette sensibilité au sel semble refléter les quantités réduites de protéines SHMT1-S31D ainsi qu’une activité plus faible ayant un impact sur le métabolisme des feuilles, entraînant une sous-accumulation de proline et une suraccumulation de polyamines. La mutation S31D de la protéine SHMT1 a également entraîné une réduction de la fermeture stomatique induite par le sel et l'ABA. Ainsi, nos résultats soulignent l’importance du maintien de l’activité du SHMT1 photorespiratoire dans des conditions de stress dû au sel et à la sécheresse et indiquent que la phosphorylation de SHMT1 S31 pourrait être impliquée dans la modulation de la stabilité de la protéine SHMT1. | Photorespiration is an essential process in oxygenic photosynthetic organisms, and it is triggered by the oxygenase activity of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (RuBisCO) to produce one molecular 3-phosphoglycerate and one molecular 2-phosphoglycolate. The toxic 2-PG is recycled by the photorespiratory pathway which includes eight core enzymes and takes place in chloroplasts, peroxisomes and metochondria and cytosol. Although the photorespiration leads to a reduced efficiency of the photosynthetic CO₂ assimilation and thereby is considered as a wasteful process, the growth phenotype of the photorespiratory enzymes can reflect the importance of this process in normal growth and development of air-grown plants. Normally, for most photorespiratory enzyme mutants, they exhibit small, chlorotic plants sometimes non-viable in air which are not observed when the mutants are grown under high CO₂ condition that limit the photorespiration by reducing the RuBisCO oxygenase activity. Photorespiratory cycle interacts with several major primary metabolic pathways, thus is a highly regulated and extensive works. Current data show that seven of eight core photorespiratory enzymes could be phosphorylated and the protein phosphorylation seems to be a critical regulatory component of the photorespiratory cycle. In order to better understand the regulation of the photorespiratory cycle, we explored the effect of SHMT1 and HPR1 phosphorylation/non-phosphorylation events on plant physiology and metabolism by several methods: Site-directed mutagenesis assay, complementation assay, activity assay, stomatal aperture assays, plant salt/drought resistance assays, metabolites measurement, gas exchange measurement. The results show the phosphorylation mimicking version of HPR1 at T335 results to a less HPR1 activity and retarded growth at the ambient air condition. For the phosphorylation mimicking version of SHMT1 at S31 resulted in a less stability leading to a reduced resistance to drought and salt stress. The decline of resistance against abiotic stress was mainly due to impairment in the closure of stomata which were unable to respond properly to ABA probably because of a default in the PLC pathway. So there results indicate that the phosphorylation of SHTM1 leads to a negative effect for the plant growth especially under stress condition. Thus, we propose that the SHMT1 can be phosphorylated at a basic level under normal growth conditions, once the photorespiratory flux is increased such under salt stress condition, the SHMT1 should be dephosphorylated to stabilize SHMT1 and sustain a high photorespiration flux to cope with reduced CO₂ availability.

Photorespiration is an essential process in oxygenic photosynthetic organisms, and it is triggered by the oxygenase activity of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (RuBisCO) to produce one molecular 3-phosphoglycerate and one molecular 2-phosphoglycolate. The toxic 2-PG is recycled by the photorespiratory pathway which includes eight core enzymes and takes place in chloroplasts, peroxisomes and metochondria and cytosol. Although the photorespiration leads to a reduced efficiency of the photosynthetic CO₂ assimilation and thereby is considered as a wasteful process, the growth phenotype of the photorespiratory enzymes can reflect the importance of this process in normal growth and development of air-grown plants. Normally, for most photorespiratory enzyme mutants, they exhibit small, chlorotic plants sometimes non-viable in air which are not observed when the mutants are grown under high CO₂ condition that limit the photorespiration by reducing the RuBisCO oxygenase activity. Photorespiratory cycle interacts with several major primary metabolic pathways, thus is a highly regulated and extensive works. Current data show that seven of eight core photorespiratory enzymes could be phosphorylated and the protein phosphorylation seems to be a critical regulatory component of the photorespiratory cycle. In order to better understand the regulation of the photorespiratory cycle, we explored the effect of SHMT1 and HPR1 phosphorylation/non-phosphorylation events on plant physiology and metabolism by several methods: Site-directed mutagenesis assay, complementation assay, activity assay, stomatal aperture assays, plant salt/drought resistance assays, metabolites measurement, gas exchange measurement. The results show the phosphorylation mimicking version of HPR1 at T335 results to a less HPR1 activity and retarded growth at the ambient air condition. For the phosphorylation mimicking version of SHMT1 at S31 resulted in a less stability leading to a reduced resistance to drought and salt stress. The decline of resistance against abiotic stress was mainly due to impairment in the closure of stomata which were unable to respond properly to ABA probably because of a default in the PLC pathway. So there results indicate that the phosphorylation of SHTM1 leads to a negative effect for the plant growth especially under stress condition. Thus, we propose that the SHMT1 can be phosphorylated at a basic level under normal growth conditions, once the photorespiratory flux is increased such under salt stress condition, the SHMT1 should be dephosphorylated to stabilize SHMT1 and sustain a high photorespiration flux to cope with reduced CO₂ availability. | La photorespiration est un processus essential chez tous les organismes photosynthétiques. Elle est déclenchée par l’activité oxygénase de la Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (RuBisCO) menant à la production d’une molécule de 3-phosphoglycerate and une molécule de 2-phosphoglycolate (2PG). Le 2PG est toxique et sera recyclé par la photorespiration qui implique huit principales enzymes et prend place dans les chloroplastes, les peroxysomes, les mitochondries et le cytosol. Bien que la photorespiration aboutisse à une efficacité réduite de l’assimilation du CO₂ photosynthétique et soit considérée comme un processus inutile, le phénotype de croissance des mutants d’enzymes photorespiratoires (croissance réduite, chlorose) reflète l’importance de ce processus dans la croissance et le développement normal car il interagit avec plusieurs voies métaboliques primaires. Les données actuelles montrent que sept des huit principales enzymes photorespiratoires pourraient être phosphorylées et qu’ainsi la phosphorylation pourrait être un élément régulateur essentiel du cycle photorespiratoire. Afin de mieux comprendre la régulation du cycle photorespiratoire, nous avons étudié l’effet d’une phosphorylation/ absence de phosphorylation sur la sérine hydroxyméthyltransférase 1 mitochondriale (SHMT1) et de l’hydroxypyruvate réductase peroxisomale en utilisant des versions de ces enzymes mimant une phosphorylation (sérine ou la thréonine mutée en acide aspartique) ou une absence de phosphoryaltion (sérine ou thréonine mutée en alanine).Deux sites sont phosphorylés chez HPR1: S229 et T335. La mutation de ces sites montre que seule la version mimant une phosphorylation sur le site T335 (HPR1 T335D) entraîne une activité réduite de la protéine recombinante HPR1. Ce résultat a été confirmé in vivo puisque le mutant Arabidopsis hpr1 exprimant HPR1 T33D était incapable de totalement complémenter le phénotype photorespiratoire du mutant hpr1.Par complémentation du mutant d’Arabidopsis shm1-1 par une forme sauvage de SHMT1, d’une version mimant (S31D) ou non (S31A) une phosphorylation, les résultats ont montré que toutes les formes de SHMT1 pouvaient presque totalement complémenter le phénotype de croissance de shm1-1. Cependant, chaque ligne transgénique n'avait que 50% de l'activité de SHMT normale. En réponse à un stress dû au sel ou à la sécheresse, les lignées Compl-S31D ont montré un déficit de croissance plus accentué que les autres lignées transgéniques. Cette sensibilité au sel semble refléter les quantités réduites de protéines SHMT1-S31D ainsi qu’une activité plus faible ayant un impact sur le métabolisme des feuilles, entraînant une sous-accumulation de proline et une suraccumulation de polyamines. La mutation S31D de la protéine SHMT1 a également entraîné une réduction de la fermeture stomatique induite par le sel et l'ABA. Ainsi, nos résultats soulignent l’importance du maintien de l’activité du SHMT1 photorespiratoire dans des conditions de stress dû au sel et à la sécheresse et indiquent que la phosphorylation de SHMT1 S31 pourrait être impliquée dans la modulation de la stabilité de la protéine SHMT1.

International audience | In this report we investigate various strategies to boost the performance for leaf segmentation of Arabidopsis thaliana in chlorophyll fluorescent imaging without any manual annotation. Direct conversion of RGB images to gray levels picked from CVPPP challenge or from a virtual Arabidopsis thaliana simulator are tested together with synthetic noisy versions of these. Segmentation performed with a state of the art U-Net convolutional neural network is shown to benefit from these approaches with a Dice coefficient between 0.95 and 0.97 on the segmentation of the border of the leaves. A new annotated dataset of fluorescent images is made available. | In this report we investigate various strategies to boost the performance for leaf segmentation of Arabidopsis thaliana in chlorophyll fluorescent imaging without any manual annotation. Direct conversion of RGB images to gray levels picked from CVPPP challenge or from a virtual Arabidopsis thaliana simulator are tested together with synthetic noisy versions of these. Segmentation performed with a state of the art U-Net convolutional neural network is shown to benefit from these approaches with a Dice coefficient between 0.95 and 0.97 on the segmentation of the border of the leaves. A new annotated dataset of fluorescent images is made available.

International audience | Seed lots must reach set standards for commercialisation and priming is widely used by producers to enhance seed quality. This technique consists of hydration to initiate early germination processes, followed by drying prior to storage. While primed seeds exhibit faster and more uniform emergence and young seedlings are often more vigorous and resistant to abiotic stress, it is frequently reported to reduce seed longevity. Mucilage is a hydrogel of polysaccharides formed around imbibed seeds of certain species that may influence hydration and drying. To determine its effect on germination and longevity after priming we have exploited Arabidopsis thaliana mutants exhibiting different mucilage traits. Our results indicate improved longevity for seeds without mucilage following priming, which was accompanied by lower reductions in salicylic acid contents.Longevity in the seed bank contributes to the biodiversity of wild species, such as Arabidopsis thaliana, present in a given habitat. Using natural Arabidopsis thaliana variants exhibiting divergent mucilage traits under standard growth conditions, we have examined how the temperature modifications that are predicted due to climate change over the coming years affect mucilage production and properties.

The metalloid arsenic (As) is highly phytotoxic, in part due to the similarity of the arsenates to phosphates, but also due to its ability to induce reactive oxygen species (ROS) formation, and in the form of arsenite directly interact with certain enzymes. Here we aimed to determine the effects of a short period of As exposure on Arabidopsis thaliana. Particular focus was given to shoot responses, which have received less attention in previous studies. A. thaliana (ecotype Col-0) plants (28-d-old) were cultivated hydroponically in the presence of 0, 27, 108, and 216 µM arsenic in the form of sodium arsenate for five days. Translocation of As from root to shoot increased with increasing As concentration in the medium and caused a reduction in growth. Photosynthesis was severely affected due to stomatal closure, increased ROS accumulation, and alterations in expression of genes involved in oxidative stress responses and As detoxification. Primary metabolism was also perturbed, suggesting both the direct inhibition of certain enzymes as well as active defensive responses. Overall the effects of As toxicity depended greatly on the degree of translocation from root to shoot and involved both direct effects on biological processes and secondary effects caused by the accumulation of ROS.

Telomerase maturation and recruitment to telomeres is regulated by several telomerase‐ and telomere‐associated proteins. Among a number of proteins, human Pontin and Reptin play critical roles in telomerase biogenesis. Here we characterized plant orthologues of Pontin and Reptin, RuvBL1 and RuvBL2a, respectively, and show association of Arabidopsis thaliana RuvBL1 (AtRuvBL1) with the catalytic subunit of telomerase (AtTERT) in the nucleolus in vivo. In contrast to mammals, interactions between AtTERT and AtRuvBL proteins in A. thaliana are not direct and they are rather mediated by one of the Arabidopsis thaliana Telomere Repeat Binding (AtTRB) proteins. We further show that plant orthologue of dyskerin, named AtCBF5, is indirectly associated with AtTRB proteins but not with the AtRuvBL proteins in the plant nucleus/nucleolus, and interacts with the Protection of telomere 1 (AtPOT1a) in the nucleolus or cytoplasmic foci. Our genome‐wide phylogenetic analyses identify orthologues in RuvBL protein family within the plant kingdom. Dysfunction of AtRuvBL genes in heterozygous T‐DNA insertion A. thaliana mutants results in reduced telomerase activity and indicate the involvement of AtRuvBL in plant telomerase biogenesis.

Salt stress negatively affects plant growth and crop productivity. As an ideal model pathway of salt tolerance in glycophyte. To better understand the molecular mechanisms of salt-response in glycophyte, 466 of 15,768 Arabidopsis thaliana proteins with the GO term of biological with known genetic background, Arabidopsis thaliana has been widely applied to disclose the process ‘response to salt stress’ were retrieved from UniPort and analyzed by bioinformatics tools of PANTHER, DAVID, KEGG, Cytoscape and STRING. Our results not only indicated the involvement of salt-responsive proteins in various pathways and interaction networks, but also demonstrated the more complicated cross-tolerances to both abiotic stresses (osmosis, water deprivation, abscisic acid, cold, heat, light and wounding) and biotic stresses (bacterium and fungus) and multiple subcellular locations of these salt-responsive proteins. Furthermore, protein activities of superoxide dismutase (SOD) and peroxidase (POD) in Arabidopsis thaliana were determined under salt, cold and osmotic stresses, which validated the hypothesis of cross-tolerance to multiple stresses. Our work will greatly improve the current knowledge of salt tolerance mechanism in glycophytes and provide potential salt-responsive candidates for promoting plant growth and increasing crop output.

MAIN CONCLUSION: Unlike rosette leaves, the mature Arabidopsis rosette core can display full resistance to Botrytis cinerea revealing the importance for spatial and developmental aspects of plant fungal resistance. Arabidopsis thaliana is a model host to investigate plant defense against fungi. However, many of the reports investigating Arabidopsis fungal defense against the necrotrophic fungus, Botrytis cinerea, utilize rosette leaves as host tissue. Here we report organ-dependent differences in B. cinerea resistance of Arabidopsis. Although wild-type Arabidopsis rosette leaves mount a jasmonate-dependent defense that slows fungal growth, this defense is incapable of resisting fungal devastation. In contrast, as the fungus spreads through infected leaf petioles towards the plant center, or rosette core, there is a jasmonate- and age-dependent fungal penetration blockage into the rosette core. We report evidence for induced and preformed resistance in the rosette core, as direct rosette core inoculation can also result in resistance, but at a lower penetrance relative to infections that approach the core from infected leaf petioles. The Arabidopsis rosette core displays a distinct transcriptome relative to other plant organs, and BLADE ON PETIOLE (BOP) transcripts are abundant in the rosette core. The BOP genes, with known roles in abscission zone formation, are required for full Arabidopsis rosette core B. cinerea resistance, suggesting a possible role for BOP-dependent modifications that may help to restrict fungal susceptibility of the rosette core. Finally, we demonstrate that cabbage and cauliflower, common Brassicaceae crops, also display leaf susceptibility and rosette core resistance to B. cinerea that can involve leaf abscission. Thus, spatial and developmental aspects of plant host resistance play critical roles in resistance to necrotrophic fungal pathogens and are important to our understanding of plant defense mechanisms.

In this report we investigate various strategies to boost the performance for leaf segmentation of Arabidopsis thaliana in chlorophyll fluorescent imaging without any manual annotation. Direct conversion of RGB images to gray levels picked from CVPPP challenge or from a virtual Arabidopsis thaliana simulator are tested together with synthetic noisy versions of these. Segmentation performed with a state of the art U-Net convolutional neural network is shown to benefit from these approaches with a Dice coefficient between 0.95 and 0.97 on the segmentation of the border of the leaves. A new annotated dataset of fluorescent images is made available.