Mini-Review: Nod Factor Regulation of Phytohormone Signaling and Homeostasis During Rhizobia-Legume Symbiosis

The rhizobia-legume symbiosis is a mutualistic association in which bacteria provide plants with nitrogen compounds and the plant provides bacteria with carbon sources. A successful symbiotic interaction relies on a molecular dialog between the plant and the bacteria, and generally involves rhizobial lipo-chitooligosaccharide signals called Nod factors (NFs). In most cases, specific NF perception is required for rhizobia to enter root cells through newly formed intracellular structures called infection threads (ITs). Concomitantly to IT formation in root hairs, root cortical cells start to divide to create a new root organ called the nodule, which will provide the bacteria with a specific micro-environment required for symbiotic nitrogen fixation. During all these steps of plant–bacteria interaction, new plant cellular compartments and developmental programs are activated. This interaction is costly for the plant that tightly controls symbiosis establishment and functioning. Phytohormones are key regulators of cellular and developmental plasticity in plants, and they are influential endogenous signals that rapidly control plant responses. Although early symbiotic responses were known for decades to be linked to phytohormone-related responses, new data reveal the molecular mechanisms involved and links between phytohormones and the control of early symbiotic events. Reciprocally, NF signaling also targets phytohormone signaling pathways. In this review, we will focus on the emerging notion of NF and phytohormone signaling crosstalk, and how it could contribute to the tight control of symbiosis establishment in legume host plants

Towards understanding mechanisms of root development stimulation by symbiotic signals in legumes

Pour répondre aux contraintes biotiques et abiotiques de l’environnement, les plantes sont capables de modifier de manière dynamique leur croissance et leur développement. Au niveau du système racinaire, cela se manifeste par une modification du nombre, de la densité, de l’angle d’orientation et/ou de la taille des racines latérales. Cette plasticité est coordonnée par des molécules signal appelées phytohormones, qui peuvent agir de manière systémique ou locale. De plus, certaines plantes ont la capacité d’établir des associations à bénéfices réciproques avec des micro-organismes du sol. Chez certaines de ces plantes, un nouvel organe racinaire, appelé nodosité, est formé. A cause d’apparentes similarités avec le développement des racines, il est proposé que ce nouvel organe soit dérivé d’éléments du développement des racines latérales, qui auraient été réutilisés au cours de l’évolution. De manière intéressante, des signaux microbiens, appelés facteurs Nod et facteurs Myc, stimulent également la formation des racines latérales. Cette stimulation requiert une voie de signalisation commune, nécessaire à la mise en place des nodosités. L’auxine est une phytohormone qui promeut de manière générale le développement des racines latérales. Des travaux récents de l’équipe ont montré que l’auxine est capable d’agir de manière synergique avec les facteurs Nod pour stimuler la formation des racines latérales et que l’application de facteurs Nod potentialise la signalisation de l’auxine chez la légumineuse modèle Medicago truncatula. Cette approche transcriptomique a, par ailleurs, révélé un grand nombre de gènes dont l’expression est induite en présence de facteurs Nod et d’auxine. Un de ces gènes est MtIAA7, qui est exprimé préférentiellement dans les racines. MtIAA7 appartient à une famille de gènes appelée « AUX/IAA » qui sont normalement des régulateurs négatifs de la voie de signalisation de l’auxine. Le but de ce travail était d’explorer le rôle de MtIAA7 dans la stimulation du développement racinaire induit par les facteurs Nod ainsi que dans la nodulation chez Medicago truncatula, et de caractériser au niveau moléculaire sa fonction en tant que protéine AUX/IAA dont la structure n’est pas canonique. Pour cela, nous avons utilisé une approche de génétique inverse. Dans ces travaux, nous avons démontré que MtIAA7, bien que présentant une structure non canonique de protéine AUX/IAA, est un régulateur négatif du développement racinaire chez Medicago truncatula. De plus, une mutation perte de fonction n’affecte que légèrement le nombre de nodosités. En utilisant une approche d’édition du génome par la technologie CRISPR afin de générer un nouvel allèle mutant de MtIAA7, nous avons obtenu un possible gain de fonction. Ce mutant, appelé MtIAA7E94Bheavy, affecte la stimulation du développement racinaire par les facteurs Nod et la sensibilité de la racine à l’auxine. L’ensemble de ces éléments suggère que nous avons identifié un nouveau régulateur négatif du développement racinaire chez Medicago truncatula, qui est nécessaire pour sa stimulation par les facteurs Nod mais n’est pas fortement impliqué dans la nodulation.In order to respond to environmental abiotic and biotic factors, plants are able to dynamically alter their growth and development. In the root system, this is manifested by plants altering their lateral root growth in terms of number, density, angle, and/or size. This plasticity is coordinated by signaling molecules called phytohormones, which are able to work in a systemic or localized manner. Furthermore, some plants have the added ability to form interactions with soil microbial organisms in a mutually beneficial manner. In some of these plants, there is a novel root structure called a nodule which is formed. Due to its similarity with lateral root development, it has been speculated that over the course of evolution of nodule structures, elements from the lateral root development program were appropriated and repurposed for this new use. Interestingly, symbiotic microbial signals, namely purified Nod and Myc factors, have been shown to stimulate lateral root development. This stimulatory action has been shown to require a common symbiotic signaling pathway that is required for nodulation. Auxin is a phytohormone that generally promotes lateral root growth. Furthermore, recent work from our group has shown that auxin is able to work synergistically with Nod factor to stimulate lateral root growth and that the application of Nod factors is also able to potentiate auxin signaling in the model legume Medicago truncatula. This transcriptomic approach has moreover found a large group of genes that are upregulated in response to auxin and Nod factor treatment. One gene identified, MtIAA7, is expressed preferentially in roots. MtIAA7 belongs to a family of genes called Aux/IAAs, which encodes proteins that are normally negative regulators of auxin signaling. The aim of this work is to explore the role of MtIAA7 in Nod factor induced lateral root formation and nodulation in Medicago truncatula, and to characterize its function as a putative (non)-canonical Aux/IAA. We have used reverse genetics approaches to achieve this end. In this work, we have demonstrated that MtIAA7, despite being a non-canonical Aux/IAA, is able to negatively regulate lateral root development in Medicago truncatula. In addition, the MtIAA7 loss of function mutation only affects subtly the nodule number. Using CRISPR genome editing strategy in an attempt to generate another loss of function allele of MtIAA7, we obtained a putative gain of function mutation. This mutant, called MtIAA7E94Bheavy, affects NF stimulation of lateral root formation and root auxin sensitivity. Altogether, this suggests that we have identified a novel regulator of root development in Medicago truncatula that is required for Nod factor stimulation of root development but does not affect nodulation

Chromatographic fingerprinting and free-radical scavenging activity of ethanol extracts of Muntingia calabura L. leaves and stems

Objective: To determine the thin-layer chromatography (TLC) fingerprint profiles and to evaluate the in vitro antioxidant activity of ethanol extracts of Muntingia calabura (M. calabura) leaves and stems. Methods: The leaves and stems were extracted using ethanol as solvent. The TLC separation of the phytochemical constituents of the leaf and ethanol extracts was carried out in ethyl acetate: n-hexane and chloroform: ethyl acetate mobile phase systems. Distinct spots were visualized under visible light, UV 254 nm, UV 366 nm and after spraying with vanillin-sulfuric acid. The 2,2-diphenyl-1-picrylhydrazyl free-radical scavenging assay was used to evaluate the antioxidant activity of the extracts. Results: Both the leaf and stem ethanol extracts at 4 mg/mL exhibited 2,2-diphenyl-1-picrylhydrazyl inhibition of more than 90%, relative to gallic acid. The results of TLC showed that the degree of resolution between the constituent spots was comparable between the two mobile phase systems using the different visualization wavelengths. Under the 254 nm visualization, few spots were observed in leaf and stem extracts. Visualization at 366 nm yielded the greatest number of observable spots of various colors in both leaf and stem extracts. More spots were visualized upon post-derivatization with vanillin-sulfuric acid in the TLC chromatograms using chloroform: ethyl acetate mobile phase, compared to those in ethyl acetate: n-hexane mobile phase. Conclusions: M. calabura exhibited very high antioxidant activity in its leaves and stems ethanol extracts, both of which are used in traditional medicine. The TLC results demonstrated the presence of diverse secondary metabolites in the leaf and stem ethanol extracts, indicating that the antioxidant activity, including other bioactivities may be attributed to these phytochemical constituents. This paper has reported for the first time the TLC fingerprinting of M. calabura using visible light, UV 254 nm, UV 366 and post-derivatization with vanillin-spray to visualize separate spots on TLC plates

Bioactive metabolite profiles and antimicrobial activity of ethanolic extracts from Muntingia calabura L. leaves and stems

Objective: To determine the bioactive phytochemicals and antimicrobial activity of leaf and stem ethanolic extracts from Muntingia calabura L. (M. calabura). Methods: Dried leaves and stems of M. calabura were extracted with 95% ethanol. The antibacterial and antifungal activities of the extracts were examined using the disc diffusion assay. The minimum inhibitory concentration (MIC) of each extract showing antimicrobial activity was determined. The dried extracts were subjected to phytochemical screening to determine the presence of bioactive components. Total phenolic and flavonoid contents were also determined by the Folin–Ciocalteu method and the aluminum chloride method, respectively. Results: Varying degrees of antimicrobial activity were exhibited by the leaf and stem extracts against Pseudomonas aeruginosa (P. aeruginosa), Salmonella typhimurium, Staphylococcus aureus (S. aureus), Bacillus subtilis, and Candida albicans (C. albicans), with minimal activity against Escherichia coli. Based on the MIC, the extracts showed the highest activity against C. albicans, S. aureus and P. aeruginosa. Phytochemical screening revealed the presence of sterols, flavonoids, alkaloids, saponins, glycosides and tannins in the leaf extract; however, no triterpenes were detected. In the stem extract, triterpenes were detected along with relative amounts of flavonoids, saponins, glycosides and tannins. Alkaloids and sterols were absent in the stem extract. Conclusions: M. calabura leaf and stem ethanol extracts are potential sources of antibacterial agents against P. aeruginosa and S. aureus. This study reports for the first time the high degree of antifungal activity of M. calabura ethanolic extract, especially against C. albicans

The moderating role of relevance on charismatic leadership and platform content to voting decision: The moderating role of relevance

An individual\u27s decision to vote is a fundamental right. The decision of each voter mark in voting for a certain candidate will be the gate way for a future of a country. In most literatures, it has been said that people vote for candidate\u27s charismatic leadership. On the other hand most literature almost state that individuals also vote for the specific platform content of candidate made in their election campaigns. As it is establish that voters give their votes to a specific platform of a candidate or a charismatic candidate, the researchers made a study on the moderating role of relevance to see if the voters personal situation and standard in life will affect how would they vote given the specifics of a certain candidate. In order to test this model, the study gathered a sample of 300 undergraduate students from different universities in the Philippines. Four conditions were used to test the moderating effect of relevance to the variables. The results showed relevance has a direct effect on charismatic leadership & voting decision and platform content & voting decision. With this being said, relevance may strengthens the relationship of charismatic leadership in predicting voting decision. Moreover, relevance strengthens the platform content in predicting voting decisio

Nod factor signaling in symbiotic nodulation

International audienceIn the rhizobial legume symbiosis, an exchange of signals leads to the specific infection of the host plant by its rhizobial symbiont and the development of specialized organs, the nodules, in which rhizobia fix nitrogen. In response to flavonoids secreted by legume roots, rhizobia notably produce lipochitooligosaccharidic molecules called Nod factors (NFs). Following extensive research, we now understand better the mechanisms of perception and transduction of the NF signal by the legume host. NF signaling results in a wide transcriptional reprogramming that leads to coordinated multistep processes of infection and nodule organogenesis, involving many plant and bacterial molecular components. Recent data suggest that the NF biosynthesis pathway evolved from non rhizobial bacteria and that NF perception/signaling in legumes adapted components preexisting in plant signaling pathways controlling in particular the establishment of the more ancient arbuscular mycorrhizal symbiosis