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Svistoonoff S.,IRD Montpellier | Benabdoun F.M.,IRD Montpellier | Benabdoun F.M.,University of Mentouri Constantine | Nambiar-Veetil M.,IRD Montpellier | And 17 more authors.
PLoS ONE | Year: 2013

Only species belonging to the Fabid clade, limited to four classes and ten families of Angiosperms, are able to form nitrogen-fixing root nodule symbioses (RNS) with soil bacteria. This concerns plants of the legume family (Fabaceae) and Parasponia (Cannabaceae) associated with the Gram-negative proteobacteria collectively called rhizobia and actinorhizal plants associated with the Gram-positive actinomycetes of the genus Frankia. Calcium and calmodulin-dependent protein kinase (CCaMK) is a key component of the common signaling pathway leading to both rhizobial and arbuscular mycorrhizal symbioses (AM) and plays a central role in cross-signaling between root nodule organogenesis and infection processes. Here, we show that CCaMK is also needed for successful actinorhiza formation and interaction with AM fungi in the actinorhizal tree Casuarina glauca and is also able to restore both nodulation and AM symbioses in a Medicago truncatula ccamk mutant. Besides, we expressed auto-active CgCCaMK lacking the auto-inhibitory/CaM domain in two actinorhizal species: C. glauca (Casuarinaceae), which develops an intracellular infection pathway, and Discaria trinervis (Rhamnaceae) which is characterized by an ancestral intercellular infection mechanism. In both species, we found induction of nodulation independent of Frankia similar to response to the activation of CCaMK in the rhizobia-legume symbiosis and conclude that the regulation of actinorhiza organogenesis is conserved regardless of the infection mode. It has been suggested that rhizobial and actinorhizal symbioses originated from a common ancestor with several independent evolutionary origins. Our findings are consistent with the recruitment of a similar genetic pathway governing rhizobial and Frankia nodule organogenesis. © 2013 Svistoonoff et al.

Diagne N.,Laboratory Mixte Intl Adaptation Des Plantes Et Microorganismes Associes Aux Stress Environnementaux | Diagne N.,Laboratoire Communications Of Microbiologie Ird Isra Ucad | Diagne N.,Institute of Forest Genetics and Tree Breeding | Arumugam K.,Institute of Forest Genetics and Tree Breeding | And 9 more authors.
BioMed Research International | Year: 2013

Degraded lands are defined by soils that have lost primary productivity due to abiotic or biotic stresses. Among the abiotic stresses, drought, salinity, and heavy metals are the main threats in tropical areas. These stresses affect plant growth and reduce their productivity. Nitrogen-fixing plants such as actinorhizal species that are able to grow in poor and disturbed soils are widely planted for the reclamation of such degraded lands. It has been reported that association of soil microbes especially the nitrogen-fixing bacteria Frankia with these actinorhizal plants can mitigate the adverse effects of abiotic and biotic stresses. Inoculation of actinorhizal plants with Frankia significantly improves plant growth, biomass, shoot and root N content, and survival rate after transplanting in fields. However, the success of establishment of actinorhizal plantation in degraded sites depends upon the choice of effective strains of Frankia. Studies related to the beneficial role of Frankia on the establishment of actinorhizal plants in degraded soils are scarce. In this review, we describe some examples of the use of Frankia inoculation to improve actinorhizal plant performances in harsh conditions for reclamation of degraded lands. © 2013 Nathalie Diagne et al.

Dieng A.,IRD Montpellier | Dieng A.,Laboratoire Communications Of Microbiologie Ird Isra Ucad | Ndoye I.,Laboratoire Communications Of Microbiologie Ird Isra Ucad | Duponnois R.,IRD Montpellier | Baudoin E.,IRD Montpellier
Soil Biology and Biochemistry | Year: 2014

The use of Jatropha curcas L. (Jatropha) as agrofuel is currently increasing in tropical and sub-tropical regions. This plant and other Jatropha species are well known for synthetising various toxicants. However, the effects of Jatropha plantation on soil microbiota have barely been investigated. We sampled three sites planted with Jatropha for 1, 2 and 15 years in Senegal, together with their adjacent fallow plots, to test whether Jatropha could have detrimental effects on microbial activity and diversity. We further hypothetised that the extent of the effects of Jatropha would be correlated to plantation age. We observed that the genetic structure of the fungal community, and especially its Glomeromycota component, was strongly affected by Jatropha in all sites. The composition of the total bacterial community, especially of the nitrogen-fixing community, was also impacted but only in 2 sites out of 3. Besides, in situ catabolic potentials shifted similarly in response to Jatropha growth. Despite these microbial shifts, we cannot conclude to a negative impact as diversity indices (catabolic potentials, genetic profiles) were not lowered. Additionally, no cumulative effect was evidenced between the youngest and the oldest Jatropha plantations, indicating that microbial shifts occurred rapidly and lasted over the long term. Further studies dedicated to the functional implications of such structural shifts are needed since the genetic structure of essential microbial communities such as mycorrhizal fungi and nitrogen-fixing bacteria were proved sensitive to Jatropha. © 2014 Elsevier Ltd.

Dieng A.,IRD Montpellier | Duponnois R.,IRD Montpellier | Floury A.,IRD Montpellier | Laguerre G.,IRD Montpellier | And 2 more authors.
Systematic and applied microbiology | Year: 2015

Jatropha curcas, a Euphorbiaceae species that produces many toxicants, is increasingly planted as an agrofuel plant in Senegal. The purpose of this study was to determine whether soil priming induced by J. curcas monoculture could alter the rhizobial populations that nodulate cowpea and acacia, two locally widespread legumes. Soil samples were transferred into a greenhouse from three fields previously cultivated with Jatropha for 1, 2, and 15 years, and the two trap legumes were grown in them. Control soil samples were also taken from adjacent Jatropha-fallow plots. Both legumes tended to develop fewer but larger nodules when grown in Jatropha soils. Nearly all the nifH sequences amplified from nodule DNA were affiliated to the Bradyrhizobium genus. Only sequences from Acacia seyal nodules grown in the most recent Jatropha plantation were related to the Mesorhizobium genus, which was much a more conventional finding on A. seyal than the unexpected Bradyrhizobium genus. Apart from this particular case, only minor differences were found in the respective compositions of Jatropha soil versus control soil rhizobial populations. Lastly, the structure of these rhizobial populations was systematically imbalanced owing to the overwhelming dominance of a very small number of nifH genotypes, some of which were identical across soil types or even sites. Despite these weak and sparse effects on rhizobial diversity, future investigations should focus on the characterization of the nitrogen-fixing abilities of the predominant rhizobial strains. Copyright © 2014 Elsevier GmbH. All rights reserved.

Passot S.,CIRAD - Agricultural Research for Development | Passot S.,Institute National Of Recherche En Informatique Et En Automatique | Gnacko F.,CIRAD - Agricultural Research for Development | Moukouanga D.,CIRAD - Agricultural Research for Development | And 20 more authors.
Frontiers in Plant Science | Year: 2016

Pearl millet plays an important role for food security in arid regions of Africa and India. Nevertheless, it is considered an orphan crop as it lags far behind other cereals in terms of genetic improvement efforts. Breeding pearl millet varieties with improved root traits promises to deliver benefits in water and nutrient acquisition. Here, we characterize early pearl millet root system development using several different root phenotyping approaches that include rhizotrons and microCT. We report that early stage pearl millet root system development is characterized by a fast growing primary root that quickly colonizes deeper soil horizons. We also describe root anatomical studies that revealed three distinct types of lateral roots that form on both primary roots and crown roots. Finally, we detected significant variation for two root architectural traits, primary root lenght and lateral root density, in pearl millet inbred lines. This study provides the basis for subsequent genetic experiments to identify loci associated with interesting early root development traits in this important cereal. © 2016 Passot, Gnacko, Moukouanga, Lucas, Guyomarc’h, Moreno Ortega, Atkinson, Belko, Bennett, Gantet, Wells, Guédon, Vigouroux, Verdeil, Muller and Laplaze.

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