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Macroscale fluorescence imaging against autofluorescence under ambient light. Light Sci Appl. 2018 Nov 28

Macroscale fluorescence imaging against autofluorescence under ambient light. Light Sci Appl. 2018 Nov 28 | Publications @IJPB | Scoop.it

Macroscale fluorescence imaging is increasingly used to observe biological samples. However, it may suffer from spectral interferences that originate from ambient light or autofluorescence of the sample or its support. In this manuscript, we built a simple and inexpensive fluorescence macroscope, which has been used to evaluate the performance of Speed OPIOM (Out of Phase Imaging after Optical Modulation), which is a reference-free dynamic contrast protocol, to selectively image reversibly photoswitchable fluorophores as labels against detrimental autofluorescence and ambient light. By tuning the intensity and radial frequency of the modulated illumination to the Speed OPIOM resonance and adopting a phase-sensitive detection scheme that ensures noise rejection, we enhanced the sensitivity and the signal-to-noise ratio for fluorescence detection in blot assays by factors of 50 and 10, respectively, over direct fluorescence observation under constant illumination. Then, we overcame the strong autofluorescence of growth media that are currently used in microbiology and realized multiplexed fluorescence observation of colonies of spectrally similar fluorescent bacteria with a unique configuration of excitation and emission wavelengths. Finally, we easily discriminated fluorescent labels from the autofluorescent and reflective background in labeled leaves, even under the interference of incident light at intensities that are comparable to sunlight. The proposed approach is expected to find multiple applications, from biological assays to outdoor observations, in fluorescence macroimaging.

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DIPOL IJPB team

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Arabidopsis thaliana DGAT3 is a [2Fe-2S] protein involved in TAG biosynthesis - Scientific Reports 22 Nov 2018

Arabidopsis thaliana DGAT3 is a [2Fe-2S] protein involved in TAG biosynthesis - Scientific Reports 22 Nov 2018 | Publications @IJPB | Scoop.it

Acyl-CoA:diacylglycerol acyltransferases 3 (DGAT3) are described as plant cytosolic enzymes synthesizing triacylglycerol. Their protein sequences exhibit a thioredoxin-like ferredoxin domain typical of a class of ferredoxins harboring a [2Fe-2S] cluster. The Arabidopsis thaliana DGAT3 (AtDGAT3; At1g48300) protein is detected in germinating seeds. The recombinant purified protein produced from Escherichia coli, although very unstable, exhibits DGAT activity in vitro. A shorter protein version devoid of its N-terminal putative chloroplast transit peptide, Δ46AtDGAT3, was more stable in vitro, allowing biochemical and spectroscopic characterization. The results obtained demonstrate the presence of a [2Fe-2S] cluster in the protein. To date, AtDGAT3 is the first metalloprotein described as a DGAT.

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DYSCOL IJPB team

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Overexpression of ATG8 in Arabidopsis stimulates autophagic activity and increases nitrogen remobilization efficiency and grain filling. Plant Cell Physiol. 2018 Nov 8

Overexpression of ATG8 in Arabidopsis stimulates autophagic activity and increases nitrogen remobilization efficiency and grain filling. Plant Cell Physiol. 2018 Nov 8 | Publications @IJPB | Scoop.it

Autophagy knock-out mutants in maize and in Arabidopsis are impaired for nitrogen recycling and exhibit reduced levels of nitrogen remobilization to their seeds. An important question is then to determine whether higher autophagy activity could at the reverse improve N remobilization efficiency and seed protein content, and under which circumstances.As autophagy machinery involves many genes amongst which 18 are important for the core machinery, the choice of which ATG gene to manipulate to increase autophagy was examined. We choose ATG8 overexpressions since it has been shown in yeast that it could increase autophagosome size and autophagic activity. The results we report here are original as they show for the first time that increasing ATG8 gene expression in plant increases autophagosome number and promotes autophagy activity. More importantly our data demonstrate that, when cultivated under full nitrate conditions, known to repress N remobilization due to sufficient N uptake from the soil, N remobilization efficiency can be nevertheless sharply and significantly increased by overexpressing ATG8 genomic sequences under the control of ubiquitin promoter. We show that overexpressors have improved seed N% and at the same time reduced N waste in their dry remains. In addition, we show that overexpressing ATG8 does not modify vegetative biomass nor harvest index, thus does not affect plant development.

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SATURNE IJPB team

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NADP-MALIC ENZYME 1 affects germination after seed storage in Arabidopsis thaliana. Plant Cell Physiol. 2018 Nov 2

NADP-MALIC ENZYME 1 affects germination after seed storage in Arabidopsis thaliana. Plant Cell Physiol. 2018 Nov 2 | Publications @IJPB | Scoop.it

Aging decreases the quality of seeds and results in agricultural and economic losses. The damage that occurs at the biochemical level can alter the seed physiological status. Although loss of viability has been investigated frequently, little information exist on the molecular and biochemical factors involved in seed deterioration and loss of viability. Oxidative stress has been implicated as a major contributor to seed deterioration and several pathways are involved in protection against this. In this study, we show that seeds of Arabidopsis thaliana lacking a functional NADP-MALIC ENZYME 1 (NADP-ME1) have reduced seed viability relative to wild type. Seeds of the nadp-me1 loss-of-function mutant display higher levels of protein carbonylation than wild type. NADP-ME1 catalyses the oxidative decarboxylation of malate to pyruvate with the simultaneous production of CO2 and NADPH. Upon seed imbibition malate and amino acids accumulate in embryos of aged seeds of the NADP-ME1 loss-of-function mutant compared to wild type. NADP-ME1 expression is increased in imbibed aged- as compared to non-aged seeds. NADP-ME1 activity at testa rupture promotes normal germination of aged seeds. In seedlings of aged seeds NADP-ME1 is specifically active in the root meristematic zone. We propose that NADP-ME1 activity is required for protecting seeds against oxidation during seed dry storage.

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PHYGERM IJPB team

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Nitrogen Limitation Alters the Response of Specific Genes to Biotic Stress - Int J Mol Sci. - 2018 Oct 27

Nitrogen Limitation Alters the Response of Specific Genes to Biotic Stress - Int J Mol Sci. - 2018 Oct 27 | Publications @IJPB | Scoop.it

In their natural environment, plants are generally confronted with multiple co-occurring stresses. However, the interaction between stresses is not well known and transcriptomic data in response to combined stresses remain scarce. This study aims at characterizing the interaction between transcriptomic responses to biotic stress and nitrogen (N) limitation. Plants were grown in low or full N, infected or not with Erwinia amylovora (Ea) and plant gene expression was analyzed through microarray and qRT-PCR. Most Ea-responsive genes had the same profile (induced/repressed) in response to Ea in low and full N. In response to stress combination, one third of modulated transcripts responded in a manner that could not be deduced from their response to each individual stress. Many defense-related genes showed a prioritization of their response to biotic stress over their response to N limitation, which was also observed using Pseudomonas syringae as a second pathosystem. Our results indicate an interaction between transcriptomic responses to N and biotic stress. A small fraction of transcripts was prioritized between antagonistic responses, reflecting a preservation of the plant defense program under N limitation. Furthermore, this interaction also led to a complex and specific response in terms of metabolism and cellular homeostasis-associated genes.

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NPI IJPB team

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NUTS IJPB team

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The HEM Lines: A New Library of Homozygous Arabidopsis thaliana EMS Mutants and its Potential to Detect Meiotic Phenotypes. - Front Plant Sci. 2018 Sep 19

The HEM Lines: A New Library of Homozygous Arabidopsis thaliana EMS Mutants and its Potential to Detect Meiotic Phenotypes. - Front Plant Sci. 2018 Sep 19 | Publications @IJPB | Scoop.it

Genetic screens have been crucial for deciphering many important biological processes, including meiosis. In Arabidopsis thaliana, previous forward screens have likely identified almost all the meiotic genes that when mutated lead to a pronounced decrease in fertility. However, the increasing number of genes identified in reverse genetics studies that play crucial roles in meiosis, but do not exhibit strong phenotypes when mutated, suggests that there are still many genes with meiotic function waiting to be discovered. In this study, we produced 897 A. thaliana homozygous mutant lines using Ethyl Methyl Sulfonate (EMS) mutagenesis followed by either single seed descent or haploid doubling. Whole genome sequencing of a subset of lines showed an average of 696 homozygous mutations per line, 195 of which (28%) modify a protein sequence. To test the power of this library, we carried out a forward screen looking for meiotic defects by observing chromosomes at metaphase I of male meiosis. Among the 649 lines analyzed, we identified 43 lines with meiotic defects. Of these, 21 lines had an obvious candidate causal mutation, namely a STOP or splicing site mutation in a gene previously shown to play a role in meiosis (ATM, MLH3, MLH1, MER3, HEI10, FLIP, ASY4, FLIP, PRD2, REC8, FANCL, and PSS1). Interestingly, this was the first time that six of these genes were identified in a forward screen in Arabidopsis (MLH3, MLH1, SGO1, PSS1, FANCL, and ASY4). These results illustrate the potential of this mutant population for screening for any qualitative or quantitative phenotype. Thus, this new mutant library is a powerful tool for functional genomics in A. thaliana. The HEM (Homozygote EMS Mutants) lines are available at the Versailles Arabidopsis stock center.

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MEIOME IJPB team

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NPR1 mediates a novel regulatory pathway in cold acclimation by interacting with HSFA1 factors. Nature Plants. 24 sept. 2018 

NPR1 mediates a novel regulatory pathway in cold acclimation by interacting with HSFA1 factors. Nature Plants. 24 sept. 2018  | Publications @IJPB | Scoop.it

NON-EXPRESSER OF PATHOGENESIS-RELATED GENES 1 (NPR1) is a master regulator of plant response to pathogens that confers immunity through a transcriptional cascade mediated by salicylic acid and TGA transcription factors. Little is known, however, about its implication in plant response to abiotic stress. Here, we provide genetic and molecular evidence supporting the fact that Arabidopsis NPR1 plays an essential role in cold acclimation by regulating cold-induced gene expression independently of salicylic acid and TGA factors. Our results demonstrate that, in response to low temperature, cytoplasmic NPR1 oligomers release monomers that translocate to the nucleus where they interact with heat shock transcription factor 1 (HSFA1) to promote the induction of HSFA1-regulated genes and cold acclimation. These findings unveil an unexpected function for NPR1 in plant response to low temperature, reveal a new regulatory pathway for cold acclimation mediated by NPR1 and HSFA1 factors, and place NPR1 as a central hub integrating cold and pathogen signalling for a better adaptation of plants to an ever-changing environment.

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AGG IJPB team

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Evidence for the control of Arabidopsis gynoecium morphogenesis by ETTIN via cell wall dynamics - Plant Physiol. - 2018 Sep 20

Evidence for the control of Arabidopsis gynoecium morphogenesis by ETTIN via cell wall dynamics - Plant Physiol. - 2018 Sep 20 | Publications @IJPB | Scoop.it
ETTIN is an atypical member of the AUXIN RESPONSE FACTOR family of transcription factors, which plays a crucial role in tissue patterning in the Arabidopsis thaliana gynoecium. Though recent insights have provided valuable information on ETT's interactions with other components of auxin signaling, the biophysical mechanisms linking ETT to its ultimate effects on gynoecium morphology were until now unknown. Here, using techniques to assess cell-wall dynamics during gynoecium growth and development, we provide a coherent body of evidence to support a model in which ETT controls the elongation of the valves tissues of the gynoecium through the positive regulation of pectin methylesterase (PME) activity in the cell wall. This increase in PME activity results in an increase in the level of demethylesterified pectins and a consequent reduction in cell wall stiffness, leading to elongation of the valves. Though similar biophysical mechanisms have been shown to act in the stem apical meristem, leading to the expansion of organ primordia, our findings represent a new case in which the regulation of cell-wall stiffness through the covalent modification of pectin has been shown to contribute to tissue patterning within a developing plant organ.
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ACCI IJPB team

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Parental transposable element loads influence their dynamics in young Nicotiana hybrids and allotetraploids - New Phytologist - 16 September 2018

Parental transposable element loads influence their dynamics in young Nicotiana hybrids and allotetraploids - New Phytologist - 16 September 2018 | Publications @IJPB | Scoop.it

The genomic shock hypothesis suggests that allopolyploidy is associated with genome changes driven by transposable elements, as a response to imbalances between parental insertion loads. To explore this hypothesis, we compared three allotetraploids Nicotiana arentsii, N. rustica and N. tabacum, which arose over comparable time frames from hybridization between increasingly divergent diploid species.

We used sequence‐specific amplification polymorphism (SSAP) to compare the dynamics of six transposable elements in these allopolyploids, their diploid progenitors, and in corresponding synthetic hybrids.

We show that element‐specific dynamics in young Nicotiana allopolyploids reflect their dynamics in diploid progenitors. Transposable element mobilization is not concomitant with immediate genome merger, but occurs within the first generations of allopolyploid formation. In natural allopolyploids, such mobilizations correlate with imbalances in the repeat profile of the parental species, which increases with their genetic divergence. Other restructuring leading to locus loss is immediate, non‐random, and targeted at specific subgenomes, independently of cross orientation.

The correlation between transposable element mobilization in allopolyploids and quantitative imbalances in parental transposable element loads supports the genome shock hypothesis proposed by McClintock.

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RETROS IJPB team

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Labeling Maize (Zea mays L.) Leaves with 15 NH4+ and Monitoring Nitrogen Incorporation into Amino Acids by GC/MS Analysis - Curr Protoc Plant Biol. 2018 Sep 3

www.ncbi.nlm.nih.gov/pubmed/30198634

The human body contains approximately 3.2% nitrogen (N), mainly present as protein and amino acids. Although N exists at a high concentration (78%) in the air, it is not readily available to animals and most plants. Plants are however able to take up both nitrate (NO3- ) and ammonium (NH4+ ) ions from the soil and convert them to amino acids and proteins, which are excellent sources for all animals. Most N is available as the stable isotope 14 N, but a second form, 15 N, is present in very low concentrations. 15 N can be detected in extracts of plants by gas chromatography followed by mass spectrometry (GC/MS). In this protocol, the methods are described for tracing the pathway by which plants are able to take up 15 N-labeled nitrate and ammonium and convert them into amino acids and proteins. A protocol for extracting and quantifying amino acids and 15 N enrichment in maize (Zea mays L.) leaves labeled with 15 NH4+ is described. Following amino acid extraction, purification, and separation by GC/MS, a calculation of the 15 N enrichment of each amino acid is carried out on a relative basis to identify any differences in the dynamics of amino acid accumulation. This will allow a study of the impact of genetic modifications or mutations on key reactions involved in primary nitrogen and carbon metabolism.

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GAPV IJPB team

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RNAi‐suppression of barley caffeic acid O‐methyltransferase modifies lignin despite redundancy in the gene family - Plant Biotechnology Journal - 2018 Aug 22

RNAi‐suppression of barley caffeic acid O‐methyltransferase modifies lignin despite redundancy in the gene family - Plant Biotechnology Journal - 2018 Aug 22 | Publications @IJPB | Scoop.it

Caffeic acid O-methyltransferase (COMT), the lignin biosynthesis gene modified in many brown-midrib high-digestibility mutants of maize and sorghum, was targeted for downregulation in the small grain temperate cereal, barley (Hordeum vulgare), to improve straw properties. Phylogenetic and expression analyses identified the barley COMT orthologue(s) expressed in stems, defining a larger gene family than in brachypodium or rice with three COMT genes expressed in lignifying tissues. RNAi significantly reduced stem COMT protein and enzyme activity, and modestly reduced stem lignin content while dramatically changing lignin structure. Lignin syringyl-to-guaiacyl ratio was reduced by ~50%, the 5-hydroxyguaiacyl (5-OH-G) unit incorporated into lignin at 10-15-fold higher levels than normal, and the amount of p-coumaric acid ester-linked to cell walls was reduced by ~50%. No brown-midrib phenotype was observed in any RNAi line despite significant COMT suppression and altered lignin. The novel COMT gene family structure in barley highlights the dynamic nature of grass genomes. Redundancy in barley COMTs may explain the absence of brown-midrib mutants in barley and wheat. The barley COMT RNAi lines nevertheless have the potential to be exploited for bioenergy applications and as animal feed.

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IJPB team

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PUX10 associates with CDC48A and regulates the dislocation of ubiquitinated oleosins from seed lipid droplets - Plant Cell, 2018 Aug 7

PUX10 associates with CDC48A and regulates the dislocation of ubiquitinated oleosins from seed lipid droplets - Plant Cell, 2018 Aug 7 | Publications @IJPB | Scoop.it
Post-germinative mobilization of neutral lipids stored in seed lipid droplets (LDs) is preceded by the degradation of oleosins, the major structural LD proteins that stabilize LDs in dry seeds. We previously showed that Arabidopsis thaliana oleosins are marked for degradation by ubiquitination, and extracted from LDs before proteolysis. However, the mechanisms underlying the dislocation of these LD-anchored proteins from the LD monolayer are yet unknown. Here, we report that PUX10, a member of the plant UBX-domain containing (PUX) protein family, is an integral LD protein that associates with a subpopulation of LDs during seed germination. In pux10 mutant seedlings, PUX10 deficiency impaired the degradation of ubiquitinated oleosins, and prevented the extraction of ubiquitinated oleosins from LDs. We also showed that PUX10 interacts with ubiquitin and CDC48A, the AAA ATPase Cell Division Cycle 48, through its UBA and UBX domains, respectively. Collectively, these results strongly suggest that PUX10 is an adaptor recruiting CDC48A to ubiquitinated oleosins, thus facilitating the dislocation of oleosins from LDs by the segregase activity of CDC48A. We propose that PUX10 and CDC48A are core components of a LD-associated degradation machinery, which we named the LD-associated degradation (LDAD) system. Importantly, PUX10 is also the first determinant of a LD subpopulation described in plants, suggesting functional differentiation of LDs in Arabidopsis seedlings.
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SPACE & DIPOL & DYSCOL IJPB teams

 

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A spatiotemporal DNA endoploidy map of the Arabidopsis root reveals roles for the endocycle in root development and stress adaptation - Plant Cell. 2018 Aug 16

A spatiotemporal DNA endoploidy map of the Arabidopsis root reveals roles for the endocycle in root development and stress adaptation - Plant Cell. 2018 Aug 16 | Publications @IJPB | Scoop.it
Somatic polyploidy caused by endoreplication is observed in arthropods, molluscs, and vertebrates, but is especially prominent in higher plants where it has been postulated to be essential for cell growth and fate maintenance. However, a comprehensive understanding of the physiological significance of plant endopolyploidy has remained elusive. Here, we modeled and experimentally verified a high-resolution DNA endoploidy map of the developing Arabidopsis thaliana root, revealing a remarkable spatiotemporal control of DNA endoploidy levels across tissues. Fitting of a simplified model to publicly available datasets profiling root gene expression under various environmental stress conditions suggested that this root endoploidy patterning may be stress-responsive. Furthermore, cellular and transcriptomic analyses revealed that inhibition of endoreplication onset alters the nuclear-to-cellular volume ratio and the expression of cell wall modifying genes, in correlation with the appearance of cell structural changes. Our data indicate that endopolyploidy might serve to coordinate cell expansion with structural stability, and that spatiotemporal endoreplication pattern changes may buffer for stress conditions, which may explain the widespread occurrence of the endocycle in plant species growing in extreme or variable environments.
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PAR IJPB team -

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Unleashing meiotic crossovers in crops. Nat Plants. 2018 Dec 4

Unleashing meiotic crossovers in crops. Nat Plants. 2018 Dec 4 | Publications @IJPB | Scoop.it

Improved plant varieties are important in our attempts to face the challenges of a growing human population and limited planet resources. Plant breeding relies on meiotic crossovers to combine favourable alleles into elite varieties1. However, meiotic crossovers are relatively rare, typically one to three per chromosome2, limiting the efficiency of the breeding process and related activities such as genetic mapping. Several genes that limit meiotic recombination were identified in the model species Arabidopsis thaliana2. Mutation of these genes in Arabidopsis induces a large increase in crossover frequency. However, it remained to be demonstrated whether crossovers could also be increased in crop species hybrids. We explored the effects of mutating the orthologues of FANCM3, RECQ44 or FIGL15 on recombination in three distant crop species, rice (Oryza sativa), pea (Pisum sativum) and tomato (Solanum lycopersicum). We found that the single recq4 mutation increases crossovers about three-fold in these crops, suggesting that manipulating RECQ4 may be a universal tool for increasing recombination in plants. Enhanced recombination could be used with other state-of-the-art technologies such as genomic selection, genome editing or speed breeding6 to enhance the pace and efficiency of plant improvement.

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MEIOME IJPB team

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Regulation of FUSCA3 expression during seed development in Arabidopsis. Plant Cell Physiol. 2018 Nov 21.

Regulation of FUSCA3 expression during seed development in Arabidopsis. Plant Cell Physiol. 2018 Nov 21. | Publications @IJPB | Scoop.it

FUSCA3 (FUS3) is a master regulator of seed development important in establishing and maintaining embryonic identity whose expression is tightly regulated at genetic and epigenetic levels. Despite this prominent role, the control of FUS3 expression remains poorly understood. Promoter and functional complementation analyses provided insight into the regulation of FUS3. W-boxes present in the promoter proximal to the start of transcription are recognised by WRKY type-1 factors which are necessary for the activation of FUS3 expression. The RY motif, binding site of B3 factors, is important for the activation of FUS3 in the embryo proper but not in the suspensor. The loss of a negative regulatory region (NRS) leads to preferential expression of FUS3 in the vasculature of vegetative tissues. Since the NRS includes the RY motif, mechanisms of activation and repression target adjacent or overlapping regions. These findings discriminate the regulation of FUS3 from that of LEAFY COTYLEDON2 by the control exerted by WRKY factors and by the presence of the RY motif, yet also confirm conservation of certain regulatory elements thereby implicating potential regulation by BASIC PENTACYSTEINE (BPC) factors and POLYCOMB REPRESSIVE COMPLEX2 (PRC2).

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SEEDEV IJPB team

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Assessment of the impact of PS3-induced resistance to downy mildew on grapevine physiology. Plant Physiol Biochem. 2018 Dec

Assessment of the impact of PS3-induced resistance to downy mildew on grapevine physiology. Plant Physiol Biochem. 2018 Dec | Publications @IJPB | Scoop.it

Elicitor-induced resistance against diseases is an attractive strategy that could contribute to reduce the use of fungicides for plant protection. However, activation of defenses has an energetic cost that plants have to fuel by a mobilization of their primary metabolism with possible adverse effect on their physiology. In this context, this study was performed to determine whether elicitor-induced resistance of grapevine leaves against downy mildew impacted its development and metabolism. The elicitor PS3 (sulfated β-glucan laminarin) was sprayed on grapevine herbaceous cuttings grown in greenhouses once or three times, and its impact was studied on young and older grapevine leaves, prior to, and after Plasmopara viticola inoculation. PS3 did not affect grapevine development during the time course of the experiment. A metabolomic analysis, mainly focused on primary metabolites, highlighted a leaf age dependent effect of PS3 treatment. Nitrogen compounds, and sugars to a lesser extent, were impacted. The results obtained complete the current knowledge of the impact of elicitor-induced resistance on plant physiology. They will be helpful to guide further experiments required to better determine the costs and benefits of elicitor-induced resistance in plants.

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IJPB platform Chemistry/Metabolism 

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Autophagy is essential for optimal Fe translocation to seeds in Arabidopsis. J Exp Bot. 2018 Nov 4

Autophagy is essential for optimal Fe translocation to seeds in Arabidopsis. J Exp Bot. 2018 Nov 4 | Publications @IJPB | Scoop.it

Micronutrient deficiencies affect a large part of the world population. They are mostly due to the consumption of grains with insufficient content of Fe or Zn. Both de novo uptake by roots and recycling from leaves may provide seeds with nutrients. Autophagy, which is a conserved mechanism for nutrient recycling in eukaryotes, was shown to be involved in nitrogen remobilization to seeds. Here, we have investigated the role of this mechanism in micronutrient translocation to seeds. We found that several Arabidopsis thaliana plants impaired in autophagy display defects in nutrient remobilization to seeds. In atg5-1 mutant, which is completely defective in autophagy, the efficiency of Fe translocation from vegetative organs to seeds was severely decreased even when Fe was provided during seed formation. Combining atg5-1 with sid2 mutation that counteracts premature senescence associated to autophagy deficiency and using 57Fe pulse labeling, we could propose a two-step mechanism in which iron taken up de novo during seed formation is first accumulated in vegetative organs and subsequently remobilized to seeds. Finally, we showed that translocations of zinc and manganese to seeds are also dependent on autophagy. Fine tuning autophagy during seed formation opens therefore new possibilities to improve micronutrient remobilization to seeds.

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SATURNE IJPB team

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Ferulate and lignin cross-links increase in cell walls of wheat grain outer layers during late development. - Plant Sci. 2018 Nov

Ferulate and lignin cross-links increase in cell walls of wheat grain outer layers during late development. - Plant Sci. 2018 Nov | Publications @IJPB | Scoop.it

Important biological, nutritional and technological roles are attributed to cell wall polymers from cereal grains. The composition of cell walls in dry wheat grain has been well studied, however less is known about cell wall deposition and modification in the grain outer layers during grain development. In this study, the composition of cell walls in the outer layers of the wheat grain (Triticum aestivum Recital cultivar) was investigated during grain development, with a focus on cell wall phenolics. We discovered that lignification of outer layers begins earlier than previously reported and long before the grain reaches its final size. Cell wall feruloylation increased in development. However, in the late stages, the amount of ferulate releasable by mild alkaline hydrolysis was reduced as well as the yield of lignin-derived thioacidolysis monomers. These reductions indicate that new ferulate-mediated cross-linkages of cell wall polymers appeared as well as new resistant interunit bonds in lignins. The formation of these additional linkages more specifically occurred in the outer pericarp. Our results raised the possibility that stiffening of cell walls occur at late development stages in the outer pericarp and might contribute to the restriction of the grain radial growth.

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APSYNTH IJPB team

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Natural variation at XND1 impacts root hydraulics and trade-off for stress responses in Arabidopsis. Nat Commun. 2018 Sep

Natural variation at XND1 impacts root hydraulics and trade-off for stress responses in Arabidopsis. Nat Commun. 2018 Sep | Publications @IJPB | Scoop.it

Soil water uptake by roots is a key component of plant performance and adaptation to adverse environments. Here, we use a genome-wide association analysis to identify the XYLEM NAC DOMAIN 1 (XND1) transcription factor as a negative regulator of Arabidopsis root hydraulic conductivity (Lpr). The distinct functionalities of a series of natural XND1 variants and a single nucleotide polymorphism that determines XND1 translation efficiency demonstrate the significance of XND1 natural variation at species-wide level. Phenotyping of xnd1 mutants and natural XND1 variants show that XND1 modulates Lpr through action on xylem formation and potential indirect effects on aquaporin function and that it diminishes drought stress tolerance. XND1 also mediates the inhibition of xylem formation by the bacterial elicitor flagellin and counteracts plant infection by the root pathogen Ralstonia solanacearum. Thus, genetic variation at XND1, and xylem differentiation contribute to resolving the major trade-off between abiotic and biotic stress resistance in Arabidopsis

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VAST IJPB team

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Emerging Functions for Cell Wall Polysaccharides Accumulated during Eudicot Seed Development. - Plants (Basel) 2018 Sep 29

Emerging Functions for Cell Wall Polysaccharides Accumulated during Eudicot Seed Development. - Plants (Basel) 2018 Sep 29 | Publications @IJPB | Scoop.it

The formation of seeds is a reproductive strategy in higher plants that enables the dispersal of offspring through time and space. Eudicot seeds comprise three main components, the embryo, the endosperm and the seed coat, where the coordinated development of each is important for the correct formation of the mature seed. In addition, the seed coat protects the quiescent progeny and can provide transport mechanisms. A key underlying process in the production of seed tissues is the formation of an extracellular matrix termed the cell wall, which is well known for its essential function in cytokinesis, directional growth and morphogenesis. The cell wall is composed of a macromolecular network of polymers where the major component is polysaccharides. The attributes of polysaccharides differ with their composition and charge, which enables dynamic remodeling of the mechanical and physical properties of the matrix by adjusting their production, modification or turnover. Accordingly, the importance of specific polysaccharides or modifications is increasingly being associated with specialized functions within seed tissues, often through the spatio-temporal accumulation or remodeling of particular polymers. Here, we review the evolution and accumulation of polysaccharides during eudicot seed development, what is known of their impact on wall architecture and the diverse roles associated with these in different seed tissues.

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PHYGERM IJPB team

www-ijpb.versailles.inra.fr/en/bs/equipes/physio-germ/index.htm

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Sphingobacterium sp. T2 manganese superoxide dismutase catalyses the oxidative demethylation of polymeric lignin via generation of hydroxyl radical - ACS Chemical Biology - September 24, 2018

Sphingobacterium sp. T2 contains two extracellular manganese superoxide dismutase enzymes which exhibit unprecedented activity for lignin oxidation, but via an unknown mechanism. Enzymatic treatment of lignin model compounds gave products whose structures were indicative of aryl-C oxidative cleavage and demethylation, as well as alkene dihydroxylation and alcohol oxidation. 18O labelling studies on the SpMnSOD-catalysed oxidation of lignin model compound guiaiacylglycerol--guaiacyl ether indicated that the oxygen atom inserted by the enzyme is derived from superoxide or peroxide. Analysis of an alkali lignin treated by SpMnSOD1 by quantitative 31P NMR spectroscopy demonstrated 20-40% increases in phenolic and aliphatic OH content, consistent with lignin demethylation and some internal oxidative cleavage reactions. Assay for hydroxyl radical generation using a fluorometric hydroxyphenylfluorescein assay revealed the release of approximately 1 molar equivalent of hydroxyl radical by SpMnSOD1. Four amino acid replacements in SpMnSOD1 were investigated, and A31H or Y27H site-directed mutant enzymes were found to show no lignin demethylation activity according to 31P NMR analysis. Structure determination of the A31H and Y27H mutant enzymes reveals the repositioning of an N-terminal protein loop, leading to widening of a solvent channel at the dimer interface, which would provide increased solvent access to the Mn centre for hydroxyl radical generation.

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IJPB team Apsynth

www-ijpb.versailles.inra.fr/en/pave/equipes/lignines-tanins/index.htm

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Increasing medium chain fatty acids production in Yarrowia lipolytica by metabolic engineering - Microbial Cell Factories - 2018 Sep 10

Increasing medium chain fatty acids production in Yarrowia lipolytica by metabolic engineering - Microbial Cell Factories - 2018 Sep 10 | Publications @IJPB | Scoop.it

Oleaginous yeast Yarrowia lipolytica is an organism of choice for the development of biofuel and oleochemicals. It has become a chassis for metabolic engineering in order to produce targeted lipids. Understanding the function of key-enzymes involved in lipid metabolism is essential to design better routes for enhanced lipid production and for strains producing lipids of interest. Because medium chain fatty acids (MCFA) are valuable compounds for biokerosene production, we previously generated strains capable of producing MCFA up to 12% of total lipid content (Rigouin et al. in ACS Synth Biol 6:1870–1879, 2017). In order to improve accumulation and content of C14 fatty acid (FA), the elongation, degradation and accumulation of these MCFA in Yarrowia lipolytica were studied. We brought evidence of the role of YALI0F0654 (YlELO1) protein in the elongation of exogenous or de novo synthesized C14 FA into C16 FA and C18 FA. YlELO1 deletion into a αFAS_I1220W expressing strain leads to the sole production of C14 FA. However, because this strain does not provide the FA essential for its growth, it requires being cultivated with essential fatty acids and C14 FA yield is limited. To promote MCFA accumulation in Y. lipolytica without compromising the growth, we overexpressed a plant diglyceride acyltransferase specific for MCFA and reached an accumulation of MCFA up to 45% of total lipid content. We characterized the role of YlELO1 in Y. lipolytica by proving its involvement in Medium chain fatty acids elongation. We showed that MCFA content can be increased in Yarrowia lipolytica by promoting their accumulation into a stable storage form (triacylglycerides) to limit their elongation and their degradation.

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Control of adventitious root formation: Insights into synergistic and antagonistic hormonal interactions - Physiologia Plantarum - 2018 Aug 29

Control of adventitious root formation: Insights into synergistic and antagonistic hormonal interactions - Physiologia Plantarum - 2018 Aug 29 | Publications @IJPB | Scoop.it

Plants have evolved sophisticated root systems that help them to cope with harsh environmental conditions. They are typically composed of a primary root (PR) and lateral roots (LRs), but may also include adventitious roots (ARs). Unlike LRs, ARs may be initiated not only from pericycle cells, but from various cell types and tissues depending on the species. Phytohormones, together with many other internal and external stimuli, coordinate and guide every step of AR formation from the first event of cell reprogramming until emergence and outgrowth. In this review we summarize recent advances in the molecular mechanisms controlling AR formation and highlight the main hormonal cross‐talk involved in its regulation under different conditions and in different model systems.

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PATS IJPB team

www-ijpb.versailles.inra.fr/en/nap/equipes/Genomique_Phloeme/index.html

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A regulatory role of autophagy for resetting the memory of heat stress in plants - Plant, Cell & Environment - 2018 Aug 22

A regulatory role of autophagy for resetting the memory of heat stress in plants - Plant, Cell & Environment - 2018 Aug 22 | Publications @IJPB | Scoop.it
As sessile life forms, plants are repeatedly confronted with adverse environmental conditions, which can impair development, growth and reproduction. During evolution, plants have established mechanisms to orchestrate the delicate balance between growth and stress tolerance, to reset cellular biochemistry once stress vanishes, or to keep a molecular memory, which enables survival of a harsher stress that may arise later. Although there are several examples of memory in diverse plants species, the molecular machinery underlying the formation, duration and resetting of stress memories is largely unknown so far. We report here that autophagy, a central self-degradative process, assists in resetting cellular memory of heat stress (HS) in Arabidopsis thaliana. Autophagy is induced by thermopriming (moderate HS) and, intriguingly, remains high long after stress termination. We demonstrate that autophagy mediates the specific degradation of heat shock proteins (HSPs) at later stages of the thermorecovery phase leading to the accumulation of protein aggregates after the second HS and a compromised heat tolerance. Autophagy mutants retain HSPs longer than wild type and concomitantly display improved thermomemory. Our findings reveal a novel regulatory mechanism for HS memory in plants.
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SATURNE IJPB Team

www-ijpb.versailles.inra.fr/en/nap/equipes/recyclazote/index.html

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One Way to Achieve Germination: Common Molecular Mechanism Induced by Ethylene and After-Ripening in Sunflower Seeds - Int J Mol Sci. 2018 Aug 20

One Way to Achieve Germination: Common Molecular Mechanism Induced by Ethylene and After-Ripening in Sunflower Seeds - Int J Mol Sci. 2018 Aug 20 | Publications @IJPB | Scoop.it
Dormancy is an adaptive trait that blocks seed germination until the environmental conditions become favorable for subsequent vegetative plant growth. Seed dormancy is defined as the inability to germinate in favorable conditions. Dormancy is alleviated during after-ripening, a dry storage period, during which dormant (D) seeds unable to germinate become non-dormant (ND), able to germinate in a wide range of environmental conditions. The treatment of dormant seeds with ethylene (D/ET) promotes seed germination, and abscisic acid (ABA) treatment reduces non-dormant (ND/ABA) seed germination in sunflowers (Helianthus annuus). Metabolomic and transcriptomic studies have been performed during imbibition to compare germinating seeds (ND and D/ET) and low-germinating seeds (D and ND/ABA). A PCA analysis of the metabolites content showed that imbibition did not trigger a significant change during the first hours (3 and 15 h). The metabolic changes associated with germination capacity occurred at 24 h and were related to hexoses, as their content was higher in ND and D/ET and was reduced by ABA treatment. At the transcriptional level, a large number of genes were altered oppositely in germinating, compared to the low-germinating seeds. The metabolomic and transcriptomic results were integrated in the interpretation of the processes involved in germination. Our results show that ethylene treatment triggers molecular changes comparable to that of after-ripening treatment, concerning sugar metabolism and ABA signaling inhibition.
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PHYGERM - IJPB team

www-ijpb.versailles.inra.fr/en/bs/equipes/physio-germ/index.htm

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