Effect of Plant Genotype on the Selection of Nodulating Rhizobium meliloti Strains

Paffetti, Donatella; Fancelli, Silvia; Daguin, Fabrice; Gnocchi, S.; Carelli, Maria; Lippi, Francesca; Scotti, Carla; Bazzicalupo, Marco

doi:10.1007/978-94-011-5159-7_190

Cited by 24 publications

(32 citation statements)

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“…The effects of single plants in the sowing year could be related to the different rates at which the root systems colonized the intertube soil layers used for sampling; in fact, the plant effect on the symbiotic population was greater in the clay soil, which also showed the greatest variation among plants for root and nodule biomass (Table 2). This is in agreement with a cultivar effect which we observed in a previous study in which a small subset of strains from the sowing year and first productive year samples was analyzed with two primers (9). At the summer 1995 sampling (fifth cut), root reconstitution had just occurred after the roots and nodules in the intertube soil layer had been removed after the first cut.…”

Section: Discussionsupporting

confidence: 90%

“…This variability has been widely investigated in the Rhizobiaceae (2,5,10,16,19), and there is some evidence of genetic exchange in populations (18). In previous work, we exploited random amplified polymorphic DNA (RAPD) techniques, combined with a powerful statistical analysis (analysis of molecular variance [AMOVA]), to describe the genetic structure of natural S. meliloti populations (8,9). Greater understanding of the genetic structure and dynamics of indigenous populations of S. meliloti would be of great agricultural interest in view of the influence that an established or varying bacterial population can have on the nodulation efficiency of particular plant cultivars.…”

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Genetic Diversity and Dynamics of Sinorhizobium meliloti Populations Nodulating Different Alfalfa Cultivars in Italian Soils

Carelli

Gnocchi

Fancelli

et al. 2000

Appl Environ Microbiol

118

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We analyzed the genetic diversity of 531 Sinorhizobium meliloti strains isolated from nodules of Medicago sativa cultivars in two different Italian soils during 4 years of plant growth. The isolates were analyzed for DNA polymorphism with the random amplified polymorphic DNA method. The populations showed a high level of genetic polymorphism distributed throughout all the isolates, with 440 different haplotypes. Analysis of molecular variance allowed us to relate the genetic structure of the symbiotic population to various factors, including soil type, alfalfa cultivar, individual plants within a cultivar, and time. Some of these factors significantly affected the genetic structure of the population, and their relative influence changed with time. At the beginning of the experiment, the soil of origin and, even more, the cultivar significantly influenced the distribution of genetic variability of S. meliloti. After 3 years, the rhizobium population was altered; it showed a genetic structure based mainly on differences among plants, while the effects of soil and cultivar were not significant. Alfalfa (Medicago sativa) and its symbiont Sinorhizobium meliloti have a long history of coexistence and coevolution. In every region where alfalfa has been cultivated for centuries, the natural nodulating population of S. meliloti plays a major role in satisfying the nitrogen requirements of the plants. Thus, it is important to investigate the genetic structure of natural populations of S. meliloti and their dynamics in relation to the host plant.In recent years, the use of molecular techniques has stimulated the development of rapid and simple methods for characterizing natural microbial populations. Studies utilizing restriction fragment length polymorphism-PCR, multilocus enzyme electrophoresis, 16S ribosomal DNA analysis, repetitive extragenic palindromic-PCR, and DNA reassociation (1, 2, 4-7, 12, 15, 17) have revealed extensive genetic variability of microbial communities in natural soil. This variability has been widely investigated in the Rhizobiaceae (2,5,10,16,19), and there is some evidence of genetic exchange in populations (18). In previous work, we exploited random amplified polymorphic DNA (RAPD) techniques, combined with a powerful statistical analysis (analysis of molecular variance [AMOVA]), to describe the genetic structure of natural S. meliloti populations (8, 9). Greater understanding of the genetic structure and dynamics of indigenous populations of S. meliloti would be of great agricultural interest in view of the influence that an established or varying bacterial population can have on the nodulation efficiency of particular plant cultivars.Little is known about the evolution of natural bacterial populations through the years in relation to a host plant. Bromfield et al. (1) showed that the M. sativa cultivar had an influence on the frequency of certain phage types in a natural S. meliloti population. Rooney-Varga et al. (12) described a seasonal modification of a natural population of sulfate-redu...

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Section: Discussionsupporting

confidence: 90%

mentioning

confidence: 99%

Genetic Diversity and Dynamics of Sinorhizobium meliloti Populations Nodulating Different Alfalfa Cultivars in Italian Soils

Carelli

Gnocchi

Fancelli

et al. 2000

Appl Environ Microbiol

118

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“…It could be postulated that the plant may play an active role in controlling the strain diversity of the bacteria eventually admitted in its nodules, irrespective of their numbers in soil or rhizosphere. The phenomenon is in line with previous reports dealing with alfalfa rhizobia (Paffetti et al 1998). …”

Section: Discussionsupporting

confidence: 93%

Long term evaluation of field-released genetically modified rhizobia

Corich

Vendramin

Vian

et al. 2007

Environ. Biosafety Res.

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This is the report of the first open field release of genetically modified microorganisms (GMMs) in Italy. It covers ten years of monitoring, and follows in-field GMM dynamics from strain release to disappearance below detection limits, as well as assessment of impact on resident microorganisms. The bacteria released belong to the nitrogen fixing legume endosymbiont Rhizobium leguminosarum bv. viciae, and were engineered with non-agronomically-proficient traits, in order to assess their behavior and fate without GMM-specific positive feedback from the plant. A DNA cassette containing mercury resistance and ß-galactosidase genes was introduced in either plasmid-borne or chromosomally integrated versions, in order to test the resulting strain stability. A synthetic promoter was used to drive the lacZ gene, conferring high catabolic activity to the GMM. Two different wild-type Rhizobium backgrounds were tested, comparing a non-indigenous vs. an indigenous, highly competitive strain. The latter had much greater persistence, since it was able to survive and establish at technically detectable levels for over four years after release. Selection factors, such as reiterated presence of the plant host, or lactose substrate supply, enhanced long-term survival to different extents. The lactose treatment showed that even a single trophic supplementation can surpass the benefits of symbiotic interaction for a period of several years. Concerning impact, the GMMs did not alter substantially the other soil community general microbiota. However, there were some significant differences in microbiota as a consequence of the Rhizobium inoculation. This effect was observed with either the WT or GMM, and was more evident in the release of the indigenous Rhizobium. Moreover, as the indigenous GMM had its parental, dominant wild-type in the same soil, it was possible to evaluate to what extent the GMM version could result in parent displacement ("self-impact"), and how much the two rhizobia would additively contribute to nodulation.

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“…Other PCR-related techniques that have been applied to obtain DNA fingerprints of rhizobial genomes are random amplified polymorphic DNA (32) and amplified fragment length polymorphism (31). These tools have been used to examine genetic diversity among Medicago-nodulating rhizobia isolated in Croatia (3), Italy (5,19,20), Latin America (8), Tunisia (1,33), and the Caucasian and Central Asian regions (2,22). Even though with these methods the existence of genetic diversity among Medicago-nodulating rhizobia has been revealed, without sequence data it is not possible to obtain conclusive estimates of levels of their divergence.…”

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Multilocus Sequence Typing as an Approach for Population Analysis of Medicago -Nodulating Rhizobia

2006

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Multilocus sequence typing (MLST), a sequence-based method to characterize bacterial genomes, was used to examine the genetic structure in a large collection of Medicago-nodulating rhizobial strains. This is the first study where MLST has been applied in conjunction with eBURST analysis to determine the population genetic structure of nonpathogenic bacteria recovered from the soil environment. Sequence variation was determined in 10 chromosomal loci of 231 strains that predominantly originated from southwest Asia. Genetic diversity for each locus ranged from 0.351 to 0.819, and the strains examined were allocated to 91 different allelic profiles or sequence types (STs). The genus Medicago is nodulated by at least two groups of rhizobia with divergent chromosomes that have been classified as Sinorhizobium meliloti and Sinorhizobium medicae. Evidence was obtained that the degree of genetic exchange among the chromosomes across these groups is limited. The symbiosis with Medicago polymorpha of nine strains placed in one of these groups, previously identified as S. medicae, ranged from ineffective to fully effective, indicating that there was no strong relationship between symbiotic phenotype and chromosomal genotype.Plants of the genus Medicago are legumes, which have the ability to form a symbiosis with soil bacteria commonly referred to as rhizobia. This symbiosis is mutually beneficial because these bacteria, when residing in root nodules, can fix atmospheric dinitrogen into a form (ammonium) that can be used by the plant for growth. Because of this property, many legumes are essential in low-input sustainable agriculture; alfalfa (Medicago sativa) and annual medics (Medicago spp.) have worldwide application as forage and green manure crops.Over many decades there has been a concerted effort to collect and evaluate medics from various locations worldwide. Subsequent to their acquisition, plant introductions were usually evaluated for their potential application in agriculture. These programs were and are relatively easy since a plant's morphology, physiology, and performance are readily measured. By comparison, the collection of rhizobial microsymbionts, capable of nodulating these medics, has been more arbitrary since there is no efficient method to discriminate between genetically related clusters of these bacteria. Traditionally, a limited number of rhizobial cultures were isolated and then were tested on several varieties of a crop and those with the best overall performance were chosen for manufacture of inoculants. In the case of Medicago, USDA 1002 (strain 3Doa2 or ATCC 9930) was isolated in 1919 by USDA scientists in Virginia from a soil on the Arlington Farm (now the location of the Pentagon). This strain was subsequently chosen as the type for the species (then Rhizobium meliloti) based on its superior symbiotic performance.With the development of techniques in molecular biology, it has become possible to examine newly isolated cultures for a much broader array of characters. These techniques have been...

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Effect of Plant Genotype on the Selection of Nodulating Rhizobium meliloti Strains

Cited by 24 publications

References 0 publications

Genetic Diversity and Dynamics of Sinorhizobium meliloti Populations Nodulating Different Alfalfa Cultivars in Italian Soils

Genetic Diversity and Dynamics of Sinorhizobium meliloti Populations Nodulating Different Alfalfa Cultivars in Italian Soils

Long term evaluation of field-released genetically modified rhizobia

Multilocus Sequence Typing as an Approach for Population Analysis of Medicago -Nodulating Rhizobia

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