Identification of transcription factors involved in root apex responses to salt stress in Medicago truncatula

The root apex contains meristematic cells that determine root growth and architecture in the soil. Specific transcription factor (TF) genes in this region may integrate endogenous signals and external cues to achieve this. Early changes in transcriptional responses involving TF genes after a salt stress in Medicago truncatula (Mt) roots were analysed using two complementary transcriptomic approaches. Forty-six salt-regulated TF genes were identified using massive quantitative real-time RT-PCR TF profiling in whole roots. In parallel, Mt16K+ microarray analysis revealed 824 genes (including 84 TF sequences) showing significant changes (p < 0.001) in their expression in root apexes after a salt stress. Analysis of salt-stress regulation in root apexes versus whole roots showed that several TF genes have more than 30-fold expression differences including specific members of AP2/EREBP, HD-ZIP, and MYB TF families. Several salt-induced TF genes also respond to other abiotic stresses as osmotic stress, cold and heat, suggesting that they participate in a general stress response. Our work suggests that spatial differences of TF gene regulation by environmental stresses in various root regions may be crucial for the adaptation of their growth to specific soil environments

Strain-Specific Symbiotic Genes: A New Level of Control in the Intracellular Accommodation of Rhizobia Within Legume Nodule Cells

This is a short commentary on the article by Wang et al. published in MPMI Vol. 31, No. 2, pages 240-248

Différenciation des cellules symbiotiques au cours de l interaction Medicago truncatula-Sinorhizobium meliloti (implication de peptides sécrétés d origine végétale)

Les légumineuses s associent avec des bactéries du sol appelées rhizobia qui se différencient en bactéroïdes fixateurs d azote au sein de nodosités racinaires. Durant cette thèse, les mécanismes de différenciation des bactéroïdes ont été étudiés dans différentes interactions Rhizobium-légumineuse. Selon la plante hôte, les bactéroïdes sont semblables à des bactéries libres ou subissent une différenciation poussée comprenant un fort allongement cellulaire corrélé à une endoréplication massive, une peméabilisation membranaire et une perte de capacité à croître. Ce processus est caractéristique de Sinorhizobium meliloti dans les nodosités de Medicago truncatula et des symbiontes des plantes appartenant au Inverted Repeat-Lacking Clade. Au contraire, dans les autres légumineuses, la différenciation des bactéroïdes ne comprend aucune de ces étapes. Il a été montré que la différenciation irréversible des bactéroïdes est sous le contrôle de la plante et est corrélée à l expression de grandes familles de gènes codant des peptides sécrétés spécifiques des nodosités. Parmi eux, les Nodule-specific Cysteine-Rich et les Glycine-Rich Protein comprennent respectivement plus de 300 et 20 membres. Ces gènes sont exclusivement exprimés dans les cellules infectées des IRLC. Des études génomique et évolutive ont révélé que ces gènes sont regroupés dans le génome de M. truncatula et évoluent par duplication locale. Une étude de microsynténie a démontré qu ils sont absents du génome de Lotus japonicus. Une étude fonctionnelle a été initiée et indique que les NCRs sont adressés aux bactéroïdes. Finalement, ces résultats ont été discutés dans le contexte de l évolution des endosymbioses.Legume plants associate with soil bacteria called rhizobia that differentiate into nitrogen-fixing bacteroids in a symbiotic organ: the root nodule. During this thesis, the mechanisms of bacteroid differentiation have been studied in different Rhizobium-legume interactions. Depending on the host plant, bacteroids were either similar to cultured bacteria or showed striking differentiation comprising cell enlargement, massive endoreduplication, membrane permeabilization and loss of growth capacity. Such a differentiation is observed for Sinorhizobium meliloti in Medicago truncatula nodules, and for those rhizobia that interact with plants related to Medicago and belonging to the Inverted Repeat-Lacking Clade (IRLC). In the non-IRLC legumes, bacteroids do not show any of these features and bacteroids are similar to free-living bacteria. It has been demonstrated that the terminal differentiation of bacteroids is under plant control and correlated to the evolution and expression of large gene families encoding nodule-specific secreted peptides resembling antimicrobial peptides. Among them are the Nodule-specific Cysteine-Rich and the Glycine-Rich Protein families, which comprise more than 300 and 20 members respectively. They are exclusively expressed in infected cells of IRLC legumes. Genomic and evolutionary studies revealed that these genes are clustered in M. truncatula genome and evolve by local duplication. A microsynteny study showed that they are absent from Lotus japonicus genome. Functional studies of these genes have been initiated and indicate that NCRs are targeted to the bacteroids. These new results have been discussed in the frame of endosymbioses evolution.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Transcriptome analysis of the Dickeya dadantii PecS regulon during early stages of interaction with Arabidopsis thaliana : D. dadantii in planta PecS regulon

PecS is one of the major global regulators controlling the virulence of Dickeya dadantii, a broad-host-range phytopathogenic bacterium causing soft rot on several plant families. To define the PecS regulon during plant colonization, we analysed the global transcriptome profiles in wild-type and pecS mutant strains during the early colonization of the leaf surfaces and in leaf tissue just before the onset of symptoms, and found that the PecS regulon consists of more than 600 genes. About one-half of these genes are down-regulated in the pecS mutant; therefore, PecS has both positive and negative regulatory roles that may be direct or indirect. Indeed, PecS also controls the regulation of a few dozen regulatory genes, demonstrating that this global regulator is at or near the top of a major regulatory cascade governing adaptation to growth in planta. Notably, PecS acts mainly at the very beginning of infection, not only to prevent virulence gene induction, but also playing an active role in the adaptation of the bacterium to the epiphytic habitat. Comparison of the patterns of gene expression inside leaf tissues and during early colonization of leaf surfaces in the wild-type bacterium revealed 637 genes modulated between these two environments. More than 40% of these modulated genes are part of the PecS regulon, emphasizing the prominent role of PecS during plant colonization

Isolated body combustion: new French cases, old worldwide issues.

International audienceThe authors present 2 new cases of so-called spontaneous human combustion. The first observations of isolated body combustion, to use a more appropriate term, date back to the 17th century. Its main features are that some parts of the body (usually the middle third) are badly burnt to the point of being reduced to ashes, contrasting with other well-preserved body parts and the intact or nearly intact immediate vicinity of the body. Usually, combustion occurs postmortem, and a source of heat is found near the body. High concentrations of blood alcohol are frequently found but not mandatory. In all cases, ruling out homicide is a major concern

Isolated body combustion: new French cases, old worldwide issues.

International audienceThe authors present 2 new cases of so-called spontaneous human combustion. The first observations of isolated body combustion, to use a more appropriate term, date back to the 17th century. Its main features are that some parts of the body (usually the middle third) are badly burnt to the point of being reduced to ashes, contrasting with other well-preserved body parts and the intact or nearly intact immediate vicinity of the body. Usually, combustion occurs postmortem, and a source of heat is found near the body. High concentrations of blood alcohol are frequently found but not mandatory. In all cases, ruling out homicide is a major concern

Extreme specificity of NCR gene expression in Medicago truncatula

Background: Legumes form root nodules to house nitrogen fixing bacteria of the rhizobium family. The rhizobia are located intracellularly in the symbiotic nodule cells. In the legume Medicago truncatula these cells produce high amounts of Nodule-specific Cysteine-Rich (NCR) peptides which induce differentiation of the rhizobia into enlarged, polyploid and non-cultivable bacterial cells. NCRs are similar to innate immunity antimicrobial peptides. The NCR gene family is extremely large in Medicago with about 600 genes. Results: Here we used the Medicago truncatula Gene Expression Atlas (MtGEA) and other published microarray data to analyze the expression of 334 NCR genes in 267 different experimental conditions. We find that all but five of these genes are expressed in nodules but in no other plant organ or in response to any other biotic interaction or abiotic stress tested. During symbiosis, none of the genes are induced by Nod factors. The NCR genes are activated in successive waves during nodule organogenesis, correlated with bacterial infection of the nodule cells and with a specific spatial localization of their transcripts from the apical to the proximal nodule zones. However, NCR expression is not associated with nodule senescence. According to their Shannon entropy, a measure expressing tissue specificity of gene expression, the NCR genes are among the most specifically expressed genes in M. truncatula. Moreover, when activated in nodules, their expression level is among the highest of all genes. Conclusions: Together, these data show that the NCR gene expression is subject to an extreme tight regulation and is only activated during nodule organogenesis in the polyploid symbiotic cells

Complete and circularized genome sequences of five nitrogen-fixing Bradyrhizobium sp. strains isolated from root nodules of peanut, Arachis hypogaea , cultivated in Tunisia

International audienceThis manuscript reports the complete and circularized Oxford Nanopore Technologies (ONT) long read-based genome sequences of five nitrogen-fixing symbionts belonging to the genus Bradyrhizobium , isolated from root nodules of peanut ( Arachis hypogaea ) grown on soil samples collected from Tunisia

Integrated roles of BclA and DD-carboxypeptidase 1 in Bradyrhizobium differentiation within NCR-producing and NCR-lacking root nodules

International audienceLegumes harbor in their symbiotic nodule organs nitrogen fixing rhizobium bacteria called bacteroids. Some legumes produce Nodule-specific Cysteine-Rich (NCR) peptides in the nodule cells to control the intracellular bacterial population. NCR peptides have antimicrobial activity and drive bacteroids toward terminal differentiation. Other legumes do not produce NCR peptides and their bacteroids are not differentiated. Bradyrhizobia, infecting NCR-producing Aeschynomene plants, require the peptide uptake transporter BclA to cope with the NCR peptides as well as a specific peptidoglycan-modifying DD-carboxypeptidase, DD-CPase1. We show that Bradyrhizobium diazoefficiens strain USDA110 forms undifferentiated bacteroids in NCR-lacking soybean nodules. Unexpectedly, in Aeschynomene afraspera nodules the nitrogen fixing USDA110 bacteroids are hardly differentiated despite the fact that this host produces NCR peptides, suggesting that USDA110 is insensitive to the host peptide effectors and that nitrogen fixation can be uncoupled from differentiation. In agreement with the absence of bacteroid differentiation, USDA110 does not require its bclA gene for nitrogen fixing symbiosis with these two host plants. Furthermore, we show that the BclA and DD-CPase1 act independently in the NCR-induced morphological differentiation of bacteroids. Our results suggest that BclA is required to protect the rhizobia against the NCR stress but not to induce the terminal differentiation pathway

Specific Host-Responsive Associations Between Medicago truncatula Accessions and Sinorhizobium Strains

Legume plants interact with rhizobia to form nitrogen-fixing root nodules. Legume-rhizobium interactions are specific and only compatible rhizobia and plant species will lead to nodule formation. Even within compatible interactions, the genotype of both the plant and the bacterial symbiont will impact on the efficiency of nodule functioning and nitrogen-fixation activity. The model legume Medicago truncatula forms nodules with several species of the Sinorhizobium genus. However, the efficiency of these bacterial strains is highly variable. In this study, we compared the symbiotic efficiency of Sinorhizobium meliloti strains Sm1021, 102F34, and FSM-MA, and Sinorhizobium medicae strain WSM419 on the two widely used M. truncatula accessions A17 and R108. The efficiency of the interactions was determined by multiple parameters. We found a high effectiveness of the FSM-MA strain with both M. truncatula accessions. In contrast, specific highly efficient interactions were obtained for the A17-WSM419 and R108-102F34 combinations. Remarkably, the widely used Sm1021 strain performed weakly on both hosts. We showed that Sm1021 efficiently induced nodule organogenesis but cannot fully activate the differentiation of the symbiotic nodule cells, explaining its weaker performance. These results will be informative for the selection of appropriate rhizobium strains in functional studies on symbiosis using these M. truncatula accessions, particularly for research focusing on late stages of the nodulation process