Research of genetic and molecular determinants involved in the nodulated root system architecture of legumes and contributing to improved nitrogen nutrition (original) (raw)
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2016
La culture de Legumineuses presente le double interet de permettre une production de graines a haute valeur nutritionnelle sans necessite d’un apport d’engrais azote. La nutrition azotee des legumineuses depend en effet majoritairement de la fixation symbiotique de l’azote atmospherique realisee par des bacteries du sol, les rhizobia, au sein des nodosites, et dans une moindre mesure, de l’assimilation de l’azote mineral du sol par les racines.Une meilleure comprehension a ete acquise sur le controle genetique de la mise en place des racines et des nodosites et sur leur impact sur la nutrition azotee. Une grande variabilite genetique pour ces caracteres a ete mise en evidence, ainsi que l’existence de correlations genetiques entre eux. Une approche de genetique quantitative a permis d’identifier des regions genomiques pouvant etre impliquees dans leurs variations. Deux pistes d’amelioration de la nutrition azotee ont aussi ete etudiees : l’amelioration de l’acquisition d’azote par l...
Regulation of legume nodulation by acidic growth conditions
Plant Signaling & Behavior, 2013
The Development and Regulation of Legume Nodulation Many legumes have evolved to establish a symbiosis with nitrogen-fixing soil-bacteria collectively known as rhizobia (including the genera Azorhizobium, Allorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium). Rhizobia invade the roots of compatible legume plants leading to the development of specialized root structures called nodules. 1-4 Within these nodules, the nitrogenase enzyme complex of rhizobia reduces atmospheric nitrogen, an unusable form of nitrogen for plants, into ammonia, which the plant utilizes for growth and development. 5,6 Nodule formation and nitrogen fixation are energy expensive and are therefore tightly regulated to ensure a balance between nitrogen acquisition and energy expenditure. One internal control mechanism of the plant is the Autoregulation of Nodulation (AON), a regulatory process acting via long distance signaling. 1-3,7-9 AON is initiated during early nodule development by the production of a rhizobia-induced signal in the root, which is mobilised to the shoot. 10 In soybean, GmRIC1 and GmRIC2 of the CLAVATA3/ESR-related (CLE) family of peptides, have
Floriculture, Ornamental and Plant Biotechnology: Advances and Topical Issues Vol. III, 2006
Legumes have the unique capacity to interact symbiotically with rhizobia, with the formation of root nodules as a result, in which nitrogen fixation takes place. The microsymbionts offer the plant an unlimited nitrogen source by fixing atmospheric nitrogen in the newly developed organs. Because of their symbiotic nitrogen fixation capacity and the accumulation of high protein levels in their seeds, legume crops are of major importance in a sustainable ecological agriculture. Medicago truncatula and Lotus japonicus are the model legume systems for the scientific community to study the biological features of indeterminate and determinate root nodulation, respectively, but also to investigate the improvement of grain legumes. Comparative genome and syntenic studies are currently performed, resulting in a potential new tool to extend the knowledge of the model legumes to agriculturally important crops, such as soybean, alfalfa and pea. The biological and molecular researches are mainly accomplished thanks to recent advances in biotechnological techniques with newly developed tools, such as genome analysis, bioinformatics, transcriptomics, proteomics and metabolomics. The knowledge of the signaling pathways leading to nodulation could eventually result in the nodulation of non-legume crops. In this chapter, major findings are discussed with the aim at providing the reader with a clear overview of the latest insights into the legume-Rhizobium nodulation field.
Tansley Review No. 40. Developmental biology of legume nodulation
New phytologist, 1992
Many legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N.j into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be temporally and spatially coordinated. Exactly how this coordination takes place is an area of intense study. Nodule morphogenesis appears to be elicited by at least two distinct signals: one from Rhizobium, a product of the nod genes (Nod factor), and a second signal, which is generated within plant tissues after treatment with Nod factor. The identity of the second signal is unknown but changes in the balance of endogenous plant hormones or the sensitivity of plant tissues to these hormones are likely to be involved. These hormonal changes may be triggered by endogenous flavonoids produced by the root in response to inoculation with Rhizobium. There is some controversy as to whether the legume nodule is an organ sui generis or a highly derived lateral root. A resolution of this question may become more critical as attempts to induce nodules on non-legume hosts, such as rice or maize, increase in number and scope.
Nitrogenous compounds in leguminous plants translocate in the form of ureides, allantoin and allantoic acid, the oxidation products of de novo purine synthesis, from the nodules to the aerial parts. The nodules are the main sites of ureides synthesis through the coordination of the plant-bacteria association. However, aspects related to the occurrence, localization and properties associated with the enzymes involved in the assimilation of ureides in shoot tissues have not yet been fully resolved. In this study, a modified and simplified automated analysis was used to determine allantoin concentration in plant xylem exudates. The total amount of ureides translocated to the aerial parts of faba bean (Vicia faba L.) plants was quantified by the stem sap extraction method using allantoin as the internal standard. Other parameters measured at different time intervals (from sowing to harvest) included shoot and root length, symbiotic parameters, plant biomass, and the nitrogen (N) status of the stem, leaves and nodules. Two rhizobial isolates (KR1 and MR2), isolated from Pisum sativum L. var. 'Macrocarpon' and Phaseolus vulgaris L. (cv. 'Carioca 29') plants, respectively, were selected from entirely different agro-climatic regions. MR2 accumulated more ureides (587.28 mg L -1 ) than KR1 (573.33 mg L -1 ) when assessed at harvest. Plants were harvested at regular intervals for dry matter and stem-extracted exudates. Results were insignificant (P > 0.05) for different inocula, shoot and root length and nodule N, but were significant (P < 0.05) for both rhizobial isolates during nodulation. The concentration of ureides, which were compared with total N concentrations in nodules, stems and leaves, were significantly different (P < 0.01). We conclude that the percentage of N in the form of ureides, however, does not always indicate the ability of the plant to symbiotically fix N 2 .
Nodular diagnosis for ecological engineering of the symbiotic nitrogen fixation with legumes
Procedia Environmental Sciences, 2011
As a major contributor to the reduced nitrogen pool in the biosphere, symbiotic nitrogen fixation by legumes plays a critical role in a sustainable production system. However this legume contribution varies with the physico-chemical and biological conditions of the nodulated-root rhizosphere. In order to assess the abiotic and biotic constrains that might limit this symbiosis at the agroecosystem level, a nodular diagnosis is proposed with common bean as a model grain-legume, and a major source of plant proteins for world human nutrition. The engineering of the legume symbiosis is addressed by participatory assessment of bean recombinant inbred lines contrasting for their efficiency in use of phosphorous for symbiotic nitrogen fixation. With this methodology, in field-sites chosen with farmers of an area of cereal-cropping in the Mediterranean basin, a large spatial and temporal variation in the legume nodulation was found. Soil P availability was a major limiting factor of the rhizobial symbiosis. In order to relate the field measurements with progress in functional genomics of the symbiosis, in situ RT-PCR on nodule sections has been implemented showing that the phytase gene is expressed in the cortex with significantly higher number of transcripts in P-efficient RILs. It is concluded that various tools and indicators are available for developing the ecological engineering of the rhizobial symbiosis, in particular for its beneficial contribution to the bio-geochemical cycle of N, and also P and C.
Non-rhizobial nodulation in legumes
… . Molec. Biol. Rev, 2007
Members of the leguminosae form the largest plant family on earth with around 19,000 species (Polhill et al., 1981). The success of legumes can largely be attributed to their ability to form a nitrogen-fixing symbiosis with specific bacteria known as rhizobia, manifested by ...
The article has been written in view of the importance attached to symbiotic N2-fixation taking place in unique organs called legume root nodules under tropics and subtropics. Nodules on legume roots are formed in interaction with soil bacteria a and b rhizobia. Symbiotic interactions between compatible legume host plant and rhizobia involve a fine tuned, molecular communication between the two partners. Calcium has been reported to playa crucial role in symbiotic signaling. Nod factors are central to the initial establishment of legume -rhizobial symbiosis. Production of these signaling molecules is activated by the release of plant phenolics, mainly flavonoids, in the rhizosphere, where they induce a set of nod genes in the appropriate rhizobial strain, leading to synthesis of Nod factors. The nature of both flavonoid signal from plant and Nod factor from the microbial partner are central to the maintenance of specificity in this symbiosis, ensuring that plant accommodates only the useful bacterium. Generally the invasion of plant root occurs through an invagination of root hair cell, called infection thread, at the primary site of interaction. The infection thread spans through the entire root cortex allowing rhizobial invasion into dividing cells of nodule primordium. Rhizobia are released from infection thread into membrane enclosed compartments, where they convert from free living form to N2-fixing form named the bacteroids. Development of functional nodules requires differentiation of both plant and microbial cells. Transcriptomics and proteomics reveal truly great extent of plant and microbial differentiation. Symbiotic N2-fixation is a finely regulated process that involves carbon and energy metabolism of the host plant significantly. The process is also under regulation by N-feedback and °2 supply within the nodules. Redox balance and antioxidant defense system play important roles in establishment of legume-rhizobial symbiosis as well as nodule functioning. Longevity and N2-fixing efficiency of nodules are hugely dependent on environmental conditions prevailing in tropical and subtropical conditions.
Developmental biology of legume nodulation
New Phytologist, 1992
Many legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N2 into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be temporally and spatially coordinated. Exactly how this coordination takes place is an area of intense study. Nodule morphogenesis appears to be elicited by at least two distinct signals: one from Rhizobium, a product of the nod genes (Nod factor), and a second signal, which is generated within plant tissues after treatment with Nod factor. The identity of the second signal is unknown but changes in the balance of endogenous plant hormones or the sensitivity of plant tissues to these hormones are likely to be involved. These hormonal changes may be triggered by endogenous flavonoids produced by the root in response to inoculation with Rhizobium. There is some controversy as to whether the legume nodule is an organ sui generis or a highly derived lateral root. A resolution of this question may become more critical as attempts to induce nodules on non-legume hosts, such as rice or maize, increase in number and scope.