Joint Relay Selection and Power Allocation in Large-Scale MIMO Systems with Untrusted Relays and Passive Eavesdroppers

In this paper, a joint relay selection and power allocation (JRP) scheme is proposed to enhance the physical layer security of a cooperative network, where a multiple antennas source communicates with a single-antenna destination in presence of untrusted relays and passive eavesdroppers (Eves). The objective is to protect the data confidentially while concurrently relying on the untrusted relays as potential Eves to improve both the security and reliability of the network. To realize this objective, we consider cooperative jamming performed by the destination while JRP scheme is implemented. With the aim of maximizing the instantaneous secrecy rate, we derive a new closed-form solution for the optimal power allocation and propose a simple relay selection criterion under two scenarios of non-colluding Eves (NCE) and colluding Eves (CE). For the proposed scheme, a new closed-form expression is derived for the ergodic secrecy rate (ESR) and the secrecy outage probability as security metrics, and a new closed-form expression is presented for the average symbol error rate (SER) as a reliability measure over Rayleigh fading channels. We further explicitly characterize the high signal-to-noise ratio slope and power offset of the ESR to highlight the impacts of system parameters on the ESR. In addition, we examine the diversity order of the proposed scheme to reveal the achievable secrecy performance advantage. Finally, the secrecy and reliability diversity-multiplexing tradeoff of the optimized network are provided. Numerical results highlight that the ESR performance of the proposed JRP scheme for NCE and CE cases is increased with respect to the number of untrustworthy relays.Comment: 18 pages, 10 figures, IEEE Transactions on Information Forensics and Security (In press

A Cell Wall Proteome and Targeted Cell Wall Analyses Provide Novel Information on Hemicellulose Metabolism in Flax

International audienceExperimentally-generated (nanoLC-MS/MS) proteomic analyses of four different flax organs/tissues (inner-stem, outer-stem, leaves and roots) enriched in proteins from 3 different sub-compartments (soluble-, membrane-, and cell wall-proteins) was combined with publically available data on flax seed and whole-stem proteins to generate a flax protein database containing 2996 nonredundant total proteins. Subsequent multiple analyses (MapMan, CAZy, WallProtDB and expert curation) of this database were then used to identify a flax cell wall proteome consisting of 456 nonredundant proteins localized in the cell wall and/or associated with cell wall biosynthesis, remodeling and other cell wall related processes. Examination of the proteins present in different flax organs/tissues provided a detailed overview of cell wall metabolism and highlighted the importance of hemicellulose and pectin re-modeling in stem tissues. Phylogenetic analyses of proteins in the cell wall proteome revealed an important paralogy in the class IIIA xyloglucan endo-transglycosy-lase/hydrolase (XTH) family associated with xyloglucan endo-hydrolase activity. Immunolocalisation, FT-IR microspectroscopy, and en-zymatic fingerprinting indicated that flax fiber primary/S1 cell walls contained xyloglucans with typical substituted side chains as well as glucuronoxylans in much lower quantities. These results suggest a likely central role of xyloglucans and endotransglucosylase/hydrolase activity in flax fiber formation and cell wall remodeling processes. Molecular & Cellula

Régulation des gènes lignine chez le lin à fibres, Linum usitatissimum L.

Le lin est une plante annuelle cultivée pour ses fibres longues et ses graines oléagineuses. Les fibres sont traditionnellement employées dans l industrie textile et, depuis peu, incorporées dans des agro-matériaux. Les fibres longues sont situées dans la tige entre l écorce et le bois, en périphérie du phloème. Les cellules fibreuses sont essentiellement composées de parois secondaires dans lesquelles la teneur en lignine est faible (2% à 4%). C est pourquoi, elles sont qualifiées d hypolignifiées . En effet, une paroi secondaire classique est généralement composée de 40 à 50% de cellulose et de 20 à 30% de lignine. Ainsi, nous suggérons l'existence d'une régulation particulière lors de la mise en place de cette paroi. On ne retrouve ce type de paroi secondaire que dans de très rares cas chez les végétaux comme dans d'autres fibres phloémiennes présentes par exemple chez le chanvre, mais aussi dans les couches G du bois de tension. Le lin est donc un bon modèle d étude pour la compréhension de la régulation de la lignification des parois secondaires. Mes travaux visent ainsi à améliorer nos connaissances sur les mécanismes cellulaires et moléculaires permettant de mettre en place une telle paroi. Les raisons pour lesquelles ces fibres contiennent de faibles quantités de lignine demeurent complètement inconnues. Différentes pistes peuvent être explorées et parmi celles-ci, l'existence de phénomènes de régulations géniques spécifiques à ces types cellulaires. Les travaux réalisés dans le cadre de ma thèse s'inscrivent dans l'hypothèse de l'existence d'une régulation transcriptionnelle à ce niveau.Flax is an annual species cultivated for its fibers and seed oil. Flax bast fibers are traditionally used in textiles and since more recently, they are integrated in composite materials used in automobile and construction industries. These fibers are located between the epidermis and the secondary xylem. Their cell walls contain unusually low amounts of lignin (2 %) compared to more classical secondary cell walls (between 20 and 30 %). So we suggest the existence of a special regulatory control of lignification within these fibers. The same types of cell walls also exist in other bast fibers such as in hemp but also in the G-layer of tension wood. Flax is a suitable model to gain knowledge on the lignification process. The reason why the bast fibers are hypolignified is completely unknown and may be due to a regulatory control at the gene transcription level.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Expression de gènes "germin-like" au cours de l'embryogenèse somatique et du développement précoce chez les conifères

Les mécanismes moléculaires de l'embryogenèse somatique chez les gymnospermes ne sont pas complètement compris. Parmi les nombreuses études réalisées visant à améliorer les connaissances sur ce phénomène particulier de développement, certaines ont été menées sur l'implication et le rôle des protéines extracellulaires. Parmi elles, certaines sont des germines et GLPs dont les fonctions ne sont pas totalement connues. Elles appartiennent à une superfamille de protéines apoplastiques exprimées à des stades spécifiques de développement ou lors de stress. Dans les rares cas où une fonction enzymatique a pu être associée à ces protéines, il a été montré qu'elle entraînait la production d'H2O2 au niveau pariétal. PcGER1, un gène GLP avait déjà été isolé chez les conifères. Ses homologues chez le mélèze hybride (LmGER1) et le pin sylvestre (PsGER1) ont été caractérisés. Ces gènes GLPs ont une structure très proche et nous avons montré que les protéines correspondantes ont probablement une activité SOD générant du H2O2. Leurs séquences promotrices, conservées ont été soumises à une analyse bioinformatique révélant qu'elles possédaient dans leur partie distale de nombreux éléments cis retrouvés ans les promoteurs de gènes répondant aux hormones et/ou exprimés dans les tissus embryonnaires, ans la graine ou encore lors de la germination. L'activité du promoteur PcGER1 a été évaluée au cours de la culture de cellules BY-2. Celle-ci s'est révélée maximale en présence de 2,4-D et de BA à la fin de phase exponentielle de croissance.Une analyse par cytométrie en flux a montré que 70 à 80 % des cellules avaient un contenu en ADN en 2C. Les cellules dans lesquelles le promoteur était activé étaient en phase G1. Par ailleurs, la comparaison de l'activité du promoteur pleine longueur et de deux fragments délétés dans la partie distale montre que l'activité décroît avec la longueur du promoteur. Enfin, nous avons mis en évidence une corrélation significative entre le taux de parois et l'activité du promoteur. L'activité du promoteur LmGER1 a été évâluée en système homologue à l'aide d'un gène rapporteur au cours du développement. Nous avons pu montré que l'expression du gène était tissu-spécifique et avait lieu tout au long de l'embryogenèse somatique. Cette expression est localisée au niveau de la coiffe racinaire et des procambia vasculaires de l'hypocotyle et des cotylédons de l'embryon somatique. Au niveau des jeunes plants, l'expression de LmGER1 est située dans la nervure centrale des euphylles au niveau du système vasculaire et précisément dans le procambium vasculaire mais nous avons également pu constater une expression au niveau des cellules de garde des stomates. Enfin, une construction provoquant de l'IR-PTGS a été introduite dans des masses embryogènes de mélèze hybride afin d'évaluer l'impact de l'extinction de ces GLPs sur le phénotype embryonnaire. Les lignées embryogènes montrant une forte sous expression du gène se sont montrées incapables de maturer. Nous avons ainsi émis des hypothèses quand au rôle des GLPs dans le contrôle de l'expansion pariétale au sein d'un certain nombre de tissus.LILLE1-BU (590092102) / SudocSudocFranceF

Caractérisation fonctionnelle d'une beta-xylosidase de lin (Linum usitatissimum L.) (rôle(s) potentiel(s) dans le métabolisme pariétal)

Le lin (Linum usitatissimum) fait partie des premières plantes cultivées dans le monde. Depuis toujours il est une source de fibres (périphloèmiennes) de très grande qualité pour l'industrie textile et connait actuellement un nouvel intérêt dans l'industrie des matériaux composites. Les fibres périphloèmiennes de lin possèdent des propriétés mécaniques remarquables grâce à la structure et la composition chimique de leurs parois cellulaires. Afin d'approfondir nos connaissances concernant la mise en place de la paroi cellulaire des fibres de lin, nous avons généré des ESTs à partir de tissus externes riches en fibres. La classification fonctionnelle des ESTs a permis l'identification de séquences codant une beta xylosidase potentielle (LuBXL1). La caractérisation fonctionnelle de plantes sous-exprimant (stratégie IR-PTGS) LuBXL1 n'as pas pu permettre la mise en évidence d'un phénotype macroscopique. En revanche, des analyses microscopiques ont suggéré des modifications éventuelles de la paroi des cellules xylèmiennes. La technique d'empreinte enzymatique a démontré une augmentation relative de l'oligoxyloglucanes XXXG dans les tissus internes de lignées sousexprimant LuBX1, associée une diminution dans la quantité relative de certains oligoxylanes. Ces observations suggèrent que chez le lin la sous-expression de LuBXL1 est associée à des modifications des hémicelluloses pariétales.Flax (Linum usitatissimum) has been a source of high quality fibers (bast fibers) for several thousand years. The fibers are currently used in the textile industry but also increasingly in the fabrication of composites. The interesting mechanical properties of these bast fibers depend upon the structure and chemical composition of their cell walls. ln order to improve our knowledge about the mechanisms underlying cell wall formation in flax fibers we produced ESTs from outer tissues, rich in fibers. Functional classification of ESTs allowed the identification of sequences coding a potential beta-xylosidase (LuBXL1). LuBXL1 down-regulated (IR-PTGS) plants did not show any visible phenotype. However, microscopie analysis suggested that down-regulation could have affected xylem cell wall structure. Enzymatic Fingerprinting indicated a relative increase in the relative quantity of the XXXG oligoxyloglucans in stem inner tissues of down-regulated lines, together with a relative decrease in the quantity of certain oligoxylans. These observations suggest that the down-regulation of LuBXL1 in flax is associated with modifications in cell wall hemicelluloses.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

You Want it Sweeter: How Glycosylation Affects Plant Response to Oxidative Stress

Oxidative stress is a cellular threat which puts at risk the productivity of most of crops valorized by humankind in terms of food, feed, biomaterial, or bioenergy. It is therefore of crucial importance to understand the mechanisms by which plants mitigate thedeleterious effects of oxidizing agents. Glycosylation of antioxidant molecules and phytohormones modifies their chemical properties as well as their cellular and histological repartition. This review emphasizes the mechanisms and the outcomes of this conjugation reaction on plant ability to face growing conditions favoring oxidative stress, in mirror with the activity of deglycosylating enzymes. Pioneer evidence bridging flavonoid, glycosylation, and redox homeostasis paved the way for numerous functional analyses of UDP-glycosyltransferases (UGTs), such as the identification of their substrates and their role to circumvent oxidative stress resulting from various environmental challenges. (De)glycosylation appears as a simple chemical reaction regulating the biosynthesis and/or the activity of a myriad of specialized metabolites partaking inresponse to pathogen and abiotic stresses. This outcome underlies the possibility to valorize UGTs potential to upgrade plant adaptation and fitness in a rising context of suboptimal growing conditions subsequent to climate change.info:eu-repo/semantics/publishe

Functional analyses of cellulose synthase genes in flax (Linum usitatissimum) by virus-induced gene silencing

International audienceFlax (Linum usitatissimum) bast fibres are located in the stem cortex where they play animportant role in mechanical support. They contain high amounts of cellulose and so are usedfor linen textiles and in the composite industry. In this study, we screened the annotated flaxgenome and identified 14 distinct cellulose synthase (CESA) genes using orthologous sequencespreviously identified. Transcriptomics of ‘primary cell wall’ and ‘secondary cell wall’ flax CESAgenes showed that some were preferentially expressed in different organs and stem tissuesproviding clues as to their biological role(s) in planta. The development for the first time in flaxof a virus-induced gene silencing (VIGS) approach was used to functionally evaluate thebiological role of different CESA genes in stem tissues. Quantification of transcript accumulationshowed that in many cases, silencing not only affected targeted CESA clades, but also had animpact on other CESA genes. Whatever the targeted clade, inactivation by VIGS affected plantgrowth. In contrast, only clade 1- and clade 6-targeted plants showed modifications in outerstemtissue organization and secondary cell wall formation. In these plants, bast fibre numberand structure were severely impacted, suggesting that the targeted genes may play animportant role in the establishment of the fibre cell wall. Our results provide new fundamentalinformation about cellulose biosynthesis in flax that should facilitate future plant improvement/engineerin

Spatial regulation of monolignol biosynthesis and laccase genes control developmental and stress-related lignin in flax

Abstract Background Bast fibres are characterized by very thick secondary cell walls containing high amounts of cellulose and low lignin contents in contrast to the heavily lignified cell walls typically found in the xylem tissues. To improve the quality of the fiber-based products in the future, a thorough understanding of the main cell wall polymer biosynthetic pathways is required. In this study we have carried out a characterization of the genes involved in lignin biosynthesis in flax along with some of their regulation mechanisms. Results We have first identified the members of the phenylpropanoid gene families through a combination of in silico approaches. The more specific lignin genes were further characterized by high throughput transcriptomic approaches in different organs and physiological conditions and their cell/tissue expression was localized in the stems, roots and leaves. Laccases play an important role in the polymerization of monolignols. This multigenic family was determined and a miRNA was identified to play a role in the posttranscriptional regulation by cleaving the transcripts of some specific genes shown to be expressed in lignified tissues. In situ hybridization also showed that the miRNA precursor was expressed in the young xylem cells located near the vascular cambium. The results obtained in this work also allowed us to determine that most of the genes involved in lignin biosynthesis are included in a unique co-expression cluster and that MYB transcription factors are potentially good candidates for regulating these genes. Conclusions Target engineering of cell walls to improve plant product quality requires good knowledge of the genes responsible for the production of the main polymers. For bast fiber plants such as flax, it is important to target the correct genes from the beginning since the difficulty to produce transgenic material does not make possible to test a large number of genes. Our work determined which of these genes could be potentially modified and showed that it was possible to target different regulatory pathways to modify lignification

Lignification in the flax stem: evidence for an unusual lignin in bast fibers

International audienceIn the context of our research on cell wall formation and maturation in flax (Linum usitatissimum L.) bast fibers, we (1) confirmed the presence of lignin in bast fibers and (2) quantified and characterized the chemical nature of this lignin at two developmental stages. Histochemical methods (Weisner and Maule reagents and KMnO4-staining) indicating the presence of lignin in bast fibers at the light and electron microscope levels were confirmed by chemical analyses (acetyl bromide). In general, the lignin content in flax bast fibers varied between 1.5% and 4.2% of the dry cell wall residues (CWRs) as compared to values varying between 23.7% and 31.4% in flax xylem tissues. Immunological and chemical analyses (thioacidolysis and nitrobenzene oxidation) indicated that both flax xylem- and bast fiber-lignins were rich in guaiacyl (G) units with S/G values inferior to 0.5. In bast fibers, the highly sensitive immunological probes allowed the detection of condensed guaiacyl-type (G) lignins in the middle lamella, cell wall junctions, and in the S1 layer of the secondary wall. In addition, lower quantities of mixed guaiacyl-syringyl (GS) lignins could be detected throughout the secondary cell wall. Chemical analyses suggested that flax bast-fiber lignin is more condensed than the corresponding xylem lignin. In addition, H units represented up to 25% of the monomers released from bast-fiber lignin as opposed to a value of 1% for the corresponding xylem tissue. Such an observation indicates that the structure of flax bast-fiber lignin is significantly different from that of the more typical 'woody plant lignin', thereby suggesting that flax bast fibers represent an interesting system for studying an unusual lignification process