Variabilité après culture in vitro de gamétophytes chez deux céréales (Analyse de descendance d'haplodiploïdes d'orge (Hordeum vulgare) en conditions de tests salins in situ. Obtention de régénérants en présence de sel après gynogenèse chez le blé dur (Triticum durum))

Chez l'orge (Hordeum vu/gare, var. Tamelalt), un test salin a été effectué ih situ sur neuf descendances andro- et gynogénétiques, dont les régénérants ont été obtenus avec ou sans NaCI dans le milieu de culture in vitro. il révèle une variabilité d'expression pour le nombre de talles, la hauteur de plante, la masse en grains et la masse de 100 grains. Les gynogénétiques, dont GOa, produisent plus de talles que les androgénétiques et que Tamelalt. Au traitement sans sel, GOa, dont le régénérant a été obtenu in vitro sans NaCI, produit 9,20% de masse en grains de plus que Tamelalt. Au traitement 5 g/L de NaCI, la masse en grains des gynogénétiques est de 16,10 à 27,12% supérieure à celle de Tamelalt. Au traitement limitant de 10 g/L de NaCI, il y a peu de différences. L'adjonction de NaCI en culture in vitro n'a pas eu d'impact sur la tolérance au sel in situ. Par ailleurs, une corrélation négative apparaît entre le nombre de grains et la masse de 100 grains. L'analyse diallèle 3x3, comprenant GOa, met en évidence en génération FI des effets d'A.G.C. significatifs pour la hauteur de plante, le nombre de talles et la masse de 100 grains, montrant que l'expression moyenne des variations est très marquée. En génération Fz, la ségrégation des caractères nombre de talles et hauteur de plante chez GOa suggère que les éléments héréditaires impliqués seraient nucléaires. Chez le blé dur (Triticum durum), le pseudo-tallage des régénérants après gynogenèse a été effectué jusqu'au 14ème repiquage. La production en pseudo-talles suit un profil linéaire ou de type exponentiel. Ceci montre que l'activité de multiplication des régénérants est spécifique de chaque unité de départ.From barley (Hordeum vu/gare, var. Tamelalt), in situ comparative saline test ofnine androgenetic and gynogenetic descents, the regenerants of which were obtained with or without NaCI in the in vitro culture medium, showed a large variability for the number of tillers, plant height, total seed weight and 100-seeds weight. The gynogenetic families produced more tillers than the androgenetics and Tamelalt. With the treatment without salt, gynogenetic GOa, the regenerant of which was obtained without NaCI in vitro, gave the best output in seeds and produced an increased seed weight of 9,20% over Tamelalt. Under 5 g/L NaCI, the seed weights of gynogenetic families showed an increase of 16,10 to 27,12% over Tamelalt. When irrigated with 10 g/L NaCI, the differences between the families are low. ln vitro salt ~ no effect on families behaviour under in situ salt stress. Furthermore, a negative correlation showed to be established between the number of seeds and 100-seeds weight. Diallel analysis 3x3, inc1uding GOa, expressed in FI generation significant GCA effects for plant height, number of tillers and 100-seeds weight, showing that average transmission of the variations re1ated to these characters was very strong. ln Fz generation, the segregation of tillers number and the plant height variations from GOa suggest that implied hereditary elements wou1d be nuclear. From durum wheat (Triticum durum), pseudo-til1ering of regenerants was carried out in vitro up to the 14th transfer. The production of pseudo-til1ers followed 1inear or exponential profile, showing a specific multiplication activity for each regenerant.NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Arabidopsis Root Development Regulation by the Endogenous Folate Precursor, Para-Aminobenzoic Acid, via Modulation of the Root Cell Cycle

The continuous growth of roots depends on their ability to maintain a balanced ratio between cell production and cell differentiation at the tip. This process is regulated by the hormonal balance of cytokinin and auxin. However, other important regulators, such as plant folates, also play a regulatory role. In this study, we investigated the impact of the folate precursor para-aminobenzoic acid (PABA) on root development. Using pharmacological, genetic, and imaging approaches, we show that the growth of Arabidopsis thaliana roots is repressed by either supplementing the growth medium with PABA or overexpressing the PABA synthesis gene GAT-ADCS. This is associated with a smaller root meristem consisting of fewer cells. Conversely, reducing the levels of free root endogenous PABA results in longer roots with extended meristems. We provide evidence that PABA represses Arabidopsis root growth in a folate-independent manner and likely acts through two mechanisms: (i) the G2/M transition of cell division in the root apical meristem and (ii) promoting premature cell differentiation in the transition zone. These data collectively suggest that PABA plays a role in Arabidopsis root growth at the intersection between cell division and cell differentiation

Reticulon-like proteins in Arabidopsis thaliana: structural organization and ER localization

International audienceReticulons are proteins that have been found predominantly associated with the endoplasmic reticulum in yeast and mammalian cells. While their functions are still poorly understood, recent findings suggest that they participate in the shaping of the tubular endoplamic reticulum (ER). Although reticulon-like proteins have been identified in plants, very little is known about their cellular localization and functions. Here, we characterized the reticulon-like protein family of Arabidopsis thaliana. Three subfamilies can be distinguished on the basis of structural organization and sequence homology. We investigated the subcellular localization of two members of the largest subfamily, i.e. AtRTNLB2 and AtRTNLB4, using fluorescent protein tags. The results demonstrate for the first time that plant reticulon-like proteins are associated with the ER. Both AtRTNLB proteins are located in the tubular ER but AtRTNLB4 is also found in the lamellar ER cisternae, and in ER tubules in close association with the chloroplasts. Similarity in protein structure and subcellular localization between AtRTNLB2 and mammalian reticulons suggests that they could assume similar basic functions inside the cell

The Arabidopsis thylakoid chloride channel AtCLCe functions in chloride homeostasis and photosynthetic regulation

Chloride ions can be translocated across cell membranes through Cl− channels or Cl−/H+ exchangers. The thylakoid-located member of the Cl− channel CLC family in Arabidopsis thaliana (AtCLCe) was hypothesized to play a role in photosynthetic regulation based on the initial photosynthetic characterization of clce mutant lines. The reduced nitrate content of Arabidopsis clce mutants suggested a role in regulation of plant nitrate homeostasis. In this study, we aimed to further investigate the role of AtCLCe in the regulation of ion homeostasis and photosynthetic processes in the thylakoid membrane. We report that the size and composition of proton motive force were mildly altered in two independent Arabidopsis clce mutant lines. Most pronounced effects in the clce mutants were observed on the photosynthetic electron transport of dark-adapted plants, based on the altered shape and associated parameters of the polyphasic OJIP kinetics of chlorophyll a fluorescence induction. Other alterations were found in the kinetics of state transition and in the macro-organisation of photosystem II supercomplexes, as indicated by circular dichroism measurements. Pre-treatment with KCl but not with KNO3 restored the wild-type photosynthetic phenotype. Analyses by transmission electron microscopy revealed a bow-like arrangement of the thylakoid network and a large thylakoid-free stromal region in chloroplast sections from the dark-adapted clce plants. Based on these data, we propose that AtCLCe functions in Cl− homeostasis after transition from light to dark, which affects chloroplast ultrastructure and regulation of photosynthetic electron transport

The Arabidopsis thylakoid transporter PHT4;1 influences phosphate availability for ATP synthesis and plant growth.

The Arabidopsis phosphate transporter PHT4;1 was previously localized to the chloroplast thylakoid membrane. Here we investigated the physiological consequences of the absence of PHT4;1 for photosynthesis and plant growth. In standard growth conditions, two independent Arabidopsis knockout mutant lines displayed significantly reduced leaf size and biomass but normal phosphorus content. When mutants were grown in high-phosphate conditions, the leaf phosphorus levels increased and the growth phenotype was suppressed. Photosynthetic measurements indicated that in the absence of PHT4;1 stromal phosphate was reduced to levels that limited ATP synthase activity. This resulted in reduced CO2 fixation and accumulation of soluble sugars, limiting plant growth. The mutants also displayed faster induction of non-photochemical quenching than the wild type, in line with the increased contribution of DeltapH to the proton-motive force across thylakoids. Small-angle neutron scattering showed a smaller lamellar repeat distance, whereas circular dichroism spectroscopy indicated a perturbed long-range order of photosystem II (PSII) complexes in the mutant thylakoids. The absence of PHT4;1 did not alter the PSII repair cycle, as indicated by wild-type levels of phosphorylation of PSII proteins, inactivation and D1 protein degradation. Interestingly, the expression of genes for several thylakoid proteins was downregulated in the mutants, but the relative levels of the corresponding proteins were either not affected or could not be discerned. Based on these data, we propose that PHT4;1 plays an important role in chloroplast phosphate compartmentation and ATP synthesis, which affect plant growth. It also maintains the ionic environment of thylakoids, which affects the macro-organization of complexes and induction of photoprotective mechanisms

Root Gravitropism Is Regulated by a Crosstalk between para-Aminobenzoic Acid, Ethylene, and Auxin

Plants respond to gravitational force through directional growth along the gravity vector. Although auxin is the central component of the root graviresponse, it works in concert with other plant hormones. Here, we show that the folate precursor para-aminobenzoic acid (PABA) is a key modulator of the auxin-ethylene interplay during root gravitropism in Arabidopsis (Arabidopsis thaliana). In gravistimulated roots, PABA promotes an asymmetric auxin response, which causes the asymmetric growth responsible for root curvature. This activity requires the auxin response transcription factors AUXIN RESPONSE FACTOR7 (ARF7) and ARF19 as well as ethylene biosynthesis and signaling, indicating that PABA activity requires both auxin and ethylene pathways. Similar to ethylene, exogenous PABA reverses the agravitropic root growth of the auxin transport mutant pin-formed2 (pin2) and the auxin biosynthetic double mutant with loss of function of weak ethylene insensitive (wei) genes, wei8wei2, but not the pin2wei8wei2 triple mutant. This finding suggests that PABA regulates the ethylene-dependent reciprocal compensation between auxin transport and biosynthesis. Furthermore, manipulation of endogenous free PABA levels by modulating the expression of the gene encoding its glucosylation enzyme, UDP-GLYCOSYL TRANSFERASE75B1, impacts the root graviresponse, suggesting that endogenous free PABA levels may play a crucial role in modulating the auxin-ethylene cross talk necessary for root gravitropism

Analysis of gene expression during parabolic flights reveals distinct early gravity responses in arabidopsis roots

Plant roots are among most intensively studied biological systems in gravity research. Altered gravity induces asymmetric cell growth leading to root bending. Differential distribution of the phytohormone auxin underlies root responses to gravity, being coordinated by auxin efflux transporters from the PIN family. The objective of this study was to compare early transcriptomic changes in roots of Arabidopsis thaliana wild type, and pin2 and pin3 mutants under parabolic flight conditions and to correlate these changes to auxin distribution. Parabolic flights allow comparison of transient 1−g, hypergravity and microgravity effects in living organisms in parallel. We found common and mutation-related genes differentially expressed in response to transient microgravity phases. Gene ontology analysis of common genes revealed lipid metabolism, response to stress factors and light categories as primarily involved in response to transient microgravity phases, suggesting that fundamental reorganisation of metabolic pathways functions upstream of a further signal mediating hormonal network. Gene expression changes in roots lacking the columella-located PIN3 were stronger than in those deprived of the epidermis and cortex cell-specific PIN2. Moreover, repetitive exposure to microgravity/hypergravity and gravity/hypergravity flight phases induced an up-regulation of auxin responsive genes in wild type and pin2 roots, but not in pin3 roots, suggesting a critical function of PIN3 in mediating auxin fluxes in response to transient microgravity phases. Our study provides important insights towards understanding signal transduction processes in transient microgravity conditions by combining for the first time the parabolic flight platform with the transcriptome analysis of different genetic mutants in the model plant, Arabidopsis