Strategies and adaptation mechanisms of legumes to low phosphorus availability in soils

Les légumineuses sont bien reconnues pour leur impact sur la durabilité des systèmes agricoles ainsi que pour leurs bienfaits nutritionnels et sanitaires. La faible disponibilité des sols en phosphore (P) est un facteur nutritionnel majeur limitant la production de légumineuses, en particulier dans les régions méditerranéennes et tropicales. La déficience en P limite la fixation de N2, car elle a été décrite comme ayant un fort impact sur la croissance et la survie des rhizobia et de la plante hôte. Les légumineuses ont évolué des mécanismes complexes pour faire face à la limitation en P.  Cette revue décrit les différents processus (modifications des racines, des anions organiques, des enzymes) qui peuvent affecter la biodisponibilité du P dans la rhizosphère. En réponse à la déficience en P, les plantes utilisent diverses stratégies adaptatives pour améliorer la disponibilité du P dans le sol et leur efficacité d'absorption, ce qui implique des modifications dans l'architecture des racines nodulées, l'acidification de la rhizosphère et l'induction de gènes impliqués dans l'efficacité d'utilisation du P, tels que les transporteurs de Pi à haute affinité et les enzymes phosphatases. Les réponses moléculaires, biochimiques, physiologiques et morphologiques sont déclenchées pour stimuler l'absorption de Pi dans le sol ou pour optimiser son efficacité d'utilisation et sa répartition intracellulaire sur tous les organes végétaux. Une compréhension holistique des mécanismes de la tolérance des légumineuses aux contraintes abiotiques sera précieuse pour les stratégies visant à améliorer l’agriculture durable dans un monde où la population augmente et les ressources renouvelables en déclin. Mots-clés : Légumineuses, poils racinaires, anions organiques, enzymes, déficience en phosphoreLegumes are well recognized for their impact in the sustainability of agricultural systems as well as for their nutritional and health benefits. Low availability of soil phosphorus (P) is one of the factors limiting the production of legumes, particularly in the Mediterranean and tropical areas. P-deficiency limits N2 fixation, since it has been described to have a strong impact on the growth and survival of both rhizobia and host plant. This review describes the different processes (root changes, role of pH, organic anions, and enzymes) that affect the availability of P in the soils. In response to P-deficiency, plants use various adaptive strategies to improve soil P availability and their uptake efficiency, which involves modifications in nodulated-root architecture, rhizosphere acidification, and induction of genes involved in P use efficiency such as high-affinity P transporters and P-hydrolyzing phosphatases enzymes. Molecular, biochemical, physiological and morphological responses are triggered to stimulate soil Pi uptake or to optimize its intracellular use efficiency and allocation over all plant organs. A holistic understanding of the key mechanisms underlying legume tolerance to abiotic constraints will be valuable for strategies to improve sustainable agriculture in a world of increasing population and declining renewable resources. Keywords: Legumes, root hairs, carboxylate, enzymes, phosphorus deficienc

High yields in a low-P tolerant recombinant inbred line of common bean under field conditions

International audienceLow phosphorus (P) availability is a primary factor that limits the production of common bean (Phaseolus vulgaris L.) in many parts of the world, especially when plant growth depends on N2 fixation. In order to understand how common bean copes with this nutritional constraint, two recombinant inbred lines (RILs) of common bean namely RILs 115 and 147 were studied in the field conditions during three growing seasons from 2012 to 2014. At flowering stage, plants were harvested and analyzed for their nodulation, growth, P content and yield. Results showed that for RIL115, the nodulation (43%), shoot (28%) and root growth (32%) was higher than for RIL147 in a low-P availability soil whatever the growing season. In addition, RIL115 had better growth and efficiency in use of P for the rhizobial symbiosis (7.29 mg nodule dry weight mg−1 nodule P) about twice higher may be involved in tolerance to low-P, and to be a useful marker for field data. At harvest, the RIL115 showed higher grain yield (1146 kg ha−1) than the RIL147 (1045 kg ha−1). It is concluded that the genotype of RIL 115 had a higher yield and could best adapt to low-P availability under field condition

Are phosphatases involved in the regulation of symbiotic nitrogen fixation under phosphorus deficiency?

In this study, we highlight the differential expression of phosphatases (APases) within the nodules of Phaseolus vulgaris under phosphorus (P) deficiency and address whether this expression might influence the nodule conductance to O2 diffusion and the subsequent respiration that supports N2 fixation in legumes. The identification of APases genes expression was performed with in situ RT-PCR methodology in nodules of two P. vulgaris recombinant inbred lines; RIL115 (Pefficient) and RIL147 (P-inefficient) grown in hydroaeroponic culture under deficient versus sufficient P supply. Our results brought the first evidence that phytase, trehalose 6-P phosphatase and fructose 1,6 bisphosphatase were differentially expressed among nodule tissues of the RIL115 and RIL147 and suggested that the abundance of their transcripts in infected cells at the vicinity of inner cortex and in outer cortex cells to be considered as new mechanism by which nodules acclimate to P deficiency. This overexpression under P deficiency coupled with increased correspondent enzyme activities and improved rhizobial use efficiency, N2 fixation and is therefore likely to play an important role in tolerance to low P availability. It is suggested that APases are involved in the osmoregulation of nodule conductance to O2 diffusion that is associated with the adaptation to environmental constraints of nitrogenase activity in the infected N2 fixing central tissues of the nodule

Genotypic variability for tolerance to low soil phosphorus availability in faba bean ( Vicia faba L.)

International audienceThe capacity of legumes to fix atmospheric dinitrogen in partnership with rhizobia provides an input-saving and resource-conserving alternative, thereby reducing the need for chemical fertilizers while enhancing overall crop productivity. However, low soil nutrient availability, notably phosphorus (P), is among the most nutrient limitations for legumes, since legume nodules responsible for N-2 fixation have a high P requirement. In order to explore the genetic variability for P uptake and use efficiency in low-P availability in soils, three faba bean genotypes namely Sidi Aich, Castel and Diva were studied in two field sites (S1 and S2) over two growing seasons 2018 and 2019. At flowering stage, plants were harvested and analyzed for their nodulation, growth, P content and yield. Results indicate that low-P availability in the soil of S1 significantly limited plant growth, nodulation, and grain yield for all genotypes though with highest extent for Diva and Castel. We found a significant correlation between nodule growth of all genotypes and Olsen-P content in the rhizosphere soil during two growing seasons. It is concluded that the genotypes selected for their P uptake and use efficiency had a higher yield and could best adapt to low-P availability under field conditions

Intercropping legumes and cereals increases resource use efficiency and crop productivity in low phosphorus soils under semi-arid Mediterranean conditions

International audienceIntercropping ensures multiple benefits like enhancement of yield, environmental security, production sustainability, and greater ecosystem services. In order to better understand how mixed crop cultures mitigate stressful conditions, this study aims to highlight the beneficial effect of the intercropping legume-cereal in enhancing nutrient uptake for plant growth and productivity in low phosphorus (P) soils. To address this question, faba bean (Vicia faba L. cv. Sidi Aich) and barley (Hordeum vulgare L. cv. Rihane 3) were grown as sole- and inter-crops over two growing seasons in 2017 and 2018 in a northern Algerian agro-ecosystem with a semiarid Mediterranean climate. The results showed that the plant growth and nodulation were significantly increased by 18% and 32%, respectively, for intercropping than for sole cropping and so more in 2018 compared to 2017. Moreover, grain yield and resource use efficiency (N and P) were significantly improved, as indicated by higher land equivalent ratio (LER > 1) in intercropping over sole cropping treatments. Also, the P and N concentrations measured in the rhizosphere were increased compared to bulk soil and even more so in the rhizosphere of intercropped species over two seasons. Our findings suggest that intercropping cereals with legumes may achieve high crop productivity and land use efficiency at reduced input levels

Are phytases involved in the regulation of symbiotic nitrogen fixation under phosphorus deficiency?

International audiencePhosphorus (P) deficiency is a critical environmental constraint that affects the growth and development of several legume crops that are usually cultivated in semi-arid regions and marginal areas. P-deficiency is known to be a significant limitation for symbiotic nitrogen fixation (SNF), and variability in SNF is strongly interlinked with the concentrations of inorganic phosphate (Pi) in the nodules. To cope with P-deficiency, legumes trigger various adaptive responses, including the induction and secretion of acid phosphatases (APases) and phytases, maintenance of Pi homeostasis in nodules and other organs, and improvement of oxygen consumption per unit of nodule mass. While the induction of phytases is a universal response to P-deficiency in higher plants, the physiological role of these enzymes in nodules of N2-fixing legume is crucial but still not fully understood. Understanding the role of APases and phytases activities in response to environmental constraints may be important in developing strategies to improve the tolerance of the nodulated legume to low-P availability. In this review, we summarize and discuss recent advances in the understanding of the expression of phytases within the nodules of legumes under P-deficiency and address whether this expression might influence the nodule respiration and contribute to adaptation of N2 fixing legumes to low-P environments. Finally, we will provide perspectives on future directions for research in this field

Expression of a phosphate-starvation inducible fructose-1,6-bisphosphatase gene in common bean nodules correlates with phosphorus use efficiency

International audienceWhile increased P-hydrolysing acid phosphatases (APase) activity in bean nodules is well documented under phosphorus (P) limitation, gene expression and subcellular localization patterns within the N2-fixing nodule tissues are poorly understood. The aim of this research was to track the enzyme activity along with the intra-nodular localization of fructose-1,6-bisphosphatase (FBPase), and its contribution to P use efficiency (PUE) under symbiotic nitrogen fixation (SNF) in Phaseolus vulgaris. The FBPase transcript were localized in situ using RT-PCR and the protein activity was measured in nodules of two contrasting recombinant inbred lines (RILs) of P. vulgaris, namely RILs 115 (P-efficient) and 147 (P-inefficient), that were grown under sufficient versus deficient P supply. Under P-deficiency, higher FBPase transcript fluorescence was found in the inner cortex as compared to the infected zone of RIL115. In addition, both the specific FBPase and total APase enzyme activities significantly increased in both RILs, but to a more significant extent in RIL115 as compared to RIL147. Furthermore, the increased FBPase activity in nodules of RIL115 positively correlated with higher use efficiency of both the rhizobial symbiosis (23%) and P for SNF (14% calculated as the ratio of N2 fixed per nodule total P content). It is concluded that the abundant tissue-specific localized FBPase transcript along with induced enzymatic activity provides evidence of a specific tolerance mechanism where N2-fixing nodules overexpress under P-deficiency conditions. Such a mechanism would maximise the intra-nodular inorganic P fraction necessary to compensate for large amount of P needed during the SNF process

Selection of Algerian lactic acid bacteria for use as antifungal bioprotective cultures and application in dairy and bakery products

In the context of a demand for “preservative-free” food products, biopreservation appears as a promising alternativeto either replace or reduce the use of chemical preservatives. The purpose of this study was to evaluatethe antifungal activity of a collection of lactic acid bacteria (n=194), and then to evaluate the applicability andefficacy of selected ones used as bioprotective cultures against mold spoilers in dairy and bakery products. First,lactic acid bacteria were isolated from various Algerian raw milk samples and Amoredj, a traditional fermentedproduct. Secondly, in vitro screening tests against Mucor racemosus UBOCC-A-109155, Penicillium communeUBOCC-A-116003, Yarrowia lipolytica UBOCC-A-216006, Aspergillus tubingensis AN, Aspergillus flavus T5 andPaecilomyces formosus AT allowed for the selection of 3 active strains, namely Lactobacillus plantarum CH1,Lactobacillus paracasei B20 and Leuconostoc mesenteroides L1. In situ tests were then performed to validate theiractivity in actual products (sour cream and sourdough bread) challenged with fungal spoilers. These testsshowed that antifungal LAB could slow the fungal target growth and could be candidates of interest for industrialapplications. Finally, organic acids and various antifungal compounds produced in sour cream and sourdoughbread by the selected LAB, and thus potentially supporting the observed antifungal activity, were identified andquantified by HPLC and LC-QTOF

Contribution of phosphatases to adaptation of rhizobial symbiosis with legumes to phosphorus deficiency

To understand the mechanisms used by legumes to improve their phosphorus use efficiency (PUE) for symbiotic nitrogen fixation under P-deficiency, an in situ RT-PCR methodology was used to localize and quantify the transcripts of candidate phosphatases genes in nodules of two common bean RILs 115 and 147 in hydro-aeroponic culture under deficient versus sufficient P supply. Our findings have revealed that expression of phytase and fructose 1,6 bisphosphatase (FBPase) genes and activities of the corresponding enzymes were positively correlated with increases both of the rhizobial symbiosis efficiency in use of P for N2 fixation and nodule O2 permeability. Under P-deficiency, this positive correlation was more significant for the P-efficient RIL115 than for theP-inefficient RIL147. It is concluded that these phosphatases play a role in adaptation to P-deficiency and are likely involved in nodule respiration linked to symbiotic nitrogen fixation

Exploring the Probiotic Potential of Dairy Industrial-Relevant Lactobacilli

Usually, the search for new candidate probiotics starts from strain isolation, followed by genotypic and phenotypic characterisations. For the best candidates, the final selection criteria, i.e., an efficient biomass production and the survival to stressful conservation processes, may often represent a bottleneck. The aim of this study is to reverse this classic bottom-up approach, thereby evaluating the in vitro probiotic properties of microbes that are already commercialized and employed in the dairy sector. The major advantage of reversing the traditional scheme is to deal with strains that are already suitable for the scale-up at the industrial level. In this work, four lactobacilli strains were analysed, belonging to the species of Lactiplantibacillus plantarum (strains PLA and PLA2) and Lacticaseibacillus rhamnosus (strains PAR4 and RHM). Both L. plantarum strains showed the best survival under simulated oro-gastrointestinal stress; PLA and PAR4 had the strongest inhibitory activity against all the tested harmful bacteria, with the latter strain showing also the highest percentage of Caco-2 adhesion; RHM was the best biofilm producer on abiotic surface. Finally, cell-free surnatants from all the strain cultures exhibited anti-inflammatory action on THP-1 macrophages. For all the studied strains, it is possible to claim beneficial functional properties other than the technological ones for which they are already marketed. The possible use of the four strains in a mixture could represent a strategy to diversify and maximize their beneficial potential. Nonetheless, future studies are necessary to validate in vivo the observed beneficial properties and to evaluate any effect of the vehicle product on the probiotic aptitude