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Vol 6, No 2 (2008)

Articles
BENEFICIAL RHIZOSPHERE PSEUDOMONADS
Lugtenberg B., Kamilova F.D.
Abstract
Among the many bacteria present on and around the root, Pseudomonas bacteria are (among) the best root colonizers and therefore very suitable to apply for beneficial purposes. In this chapter, we discuss the possibilities to use such bacteria for the following purposes: fertilization of the plant, stimulation of plant growth and yield, reduction of plant stress, and reduction of plant diseases. This research was supported by numerous grants, especially from the Dutch Organization for scientific research (NWO), EET, the European Commission and INTAS.
Ecological genetics. 2008;6(2):4-12
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EVOLUTION OF PLANT VIRUSES: ADAPTATION TO HOSTS AND VECTORS
Valkonen J.
Abstract
Viruses are obligate molecular pathogens. They depend on living host cells for their multiplication, including synthesis of the viral nucleic acids and proteins. The infection cycle of viruses in plants includes three main phases: i) replication, ii) cell to cell movement via plasmodesmata, and iii) long distance movement to different parts of the plant. During all these steps of the infection cycle viruses are challenged by the genetic variability of their hosts, which requires the virus to be adjusted to minor or major differences in virus-host interactions. These adjustments require mutations in the viral genome. Most plant viruses are also dependent on vector organisms for their spread to new host plants. The changes in virus genomes for better adaptability to the host should not compromise vector-transmissibility of progeny viruses. Host adaptation and vector adaptation can therefore be seen as the main forces influencing plant virus evolution.
Ecological genetics. 2008;6(2):13-16
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ENDOPHYTES: STRUCTURAL AND FUNCTIONAL DIVERSITY AND BIOTECHNOLOGICAL APPLICATIONS IN CONTROL OF PLANT PATHOGENS
Berg G., M?ller H., Zachow C., Opelt K., Scherwinski K., Tilcher R., Ulrich A., Hallmann J., Grosch R., Sessitsch A.
Abstract
Endophytes are an interesting group of plant-associated bacteria that live inside plants and show neutral or beneficial interaction with their host plants. The structure of bacterial communities in endophytic microenvironments of important crops (different cultivars of potato, lettuce, and sugar beet) and native plants (different bryophyte species) was analyzed by a multiphasic approach at different field sites in Europe. Interestingly, results of the cultivation-independent approaches using Single-Strand Conformation Polymorphism (SSCP) and/or Terminal Restriction Fragments Length Polymorphism (T-RFLP) of 16S rRNA genes amplified by universal as well as group-specific and functional primers revealed a high diversity and specificity of endophytic bacterial communities. The antagonistic potential of endophytic bacteria, which was determined by screening for in vitro antagonism against different pathogens (bacteria, fungi, protists, and nematodes) ranged from 5 to 43 %. An impressive, phylogenetically diverse spectrum of antagonistic strains was found. The indigenous antagonistic potential of endophytic bacteria was influenced by the plant genotype and developmental stage, the internal microenvironment, and the soil type. A screening strategy for biocontrol strains resulted in the selection of promising candidates. These strains were evaluated in greenhouse and field trials regarding their efficiency to control pathogens under in situ conditions. One product (RhizoStar®) on the basis of serratia plymuthica HRO-C48 to control Verticillium wilt on different host plants was developed. For other promising candidates likePseudomonas trivialis 3Re2-7 (B3) and serratia plymuthica 3Re4-18 (B4) a biological control strategy against the soil-borne pathogen Rhizoctonia solani will be established. These studies were funded by the Deutsche Forschungs-gemeinschaft, the Ministry of Consumer Protection, Food and Agriculture (Germany) and by private industries (KWS SAAT AG, Strawberry farm Rovershagen, and Nor-ddeutsche Pflanzenzucht Hans-Georg Lembke KG, Ho-henlieth, Germany) by grants to G.B.
Ecological genetics. 2008;6(2):17-26
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ROLE OF SIGNAL EXCHANGE IN CONTROL OF RHIZOBIUM - LEGUME SYMBIOSIS SPECIFICITY
Dolgikh E.A., Leppyanen I.V., Osipova M.A., Tikhonovich I.A.
Abstract
The signal molecules produced by legume plants and soil bacteria rhizobia and involved in early steps of symbiosis regulation were identified through the evaluation of molecular mechanisms of plant-rhizobia communication. The molecular dialog between plants and rhizobia is initiated by plant flavanoids inducing the synthesis and secretion of lipochitooligosaccharide molecules Nod factors by rhizobial bacteria. Nod factors are N-acetylglucosamine oligomers, modified by fatty acid and certain chemical groups. Nod factors trigger a set of plant reactions resulting in a formation of root nodules - nitrogen fixing symbiotic organs. Fine chemical structure of signal molecules determines host specificity of the symbiosis. Nod factors are active in low concentrations and possess mitogenic and morphogenic activity, therefore they are recognized as the new class of growth regulators. In this paper the modern data about study of Nod factor perception mechanisms and signal transduction pathway in legume plants are presented and considered with perspective for future application of these knowledge for practical increasing of symbiosis efficiency from plant side. This work was supported by RFBR 07-08-00700a (Russian Foundation of Basic Research), CRDF RUXO-012-ST-06 (BP2M12) and HIII-5399. 2008. 4, RFBR-NWO (06-04-89000-НВОЦ-а) grants.
Ecological genetics. 2008;6(2):27-34
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SIMULATION OF PLANT-BACTERIA CO-EVOLUTION IN THE MUTUALLY BENEFICIAL SYMBIOSIS
Provorov N.A., Vorobyov N.I.
Abstract
The mathematical model for evolution of legume-rhizobia mutualism based on the partners' positive feedbacks resulted from their metabolic (C-N) exchange is presented. Negative FDS in rhizobia population, combined with the partners' positive feedbacks ensure anchoring or even domination of the mutants which either acquired the mutualistic traits or changed the specificity in their expression with different host genotypes. The created model allows us to consider the mutualistic symbiosis as of a finely balanced population system in which the equilibrium may be shifted in favor of beneficial microbial genotypes due to natural selection for an improved symbiotic efficiency implemented in plant population. Research is supported by RFBR grant 06-04-48800a.
Ecological genetics. 2008;6(2):35-48
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MOLECULAR STRATEGIES AND AGRONOMIC IMPACTS OF PLANT-MICROBE SYMBIOSES
Tikhonovich I.A., Provorov N.A.
Abstract
The molecular mechanism of the agronomically important nutritional and defensive plantmicrobe symbioses are reviewed. These symbioses are based on the signaling interactions which result in the development of novel tissue/cellular structures and of extended metabolic capacities in the partners which improve greatly the adaptive potential of plants due to an increased tolerance to biotic or abiotic stresses. The molecular, genetic and ecological knowledge on plant-microbe interactions provide a strategy for a sustainable crop production based on substituting the agrochemicals (mineral fertilizers, pesticides) by the microbial inoculants. An improvement of plantmicrobe symbioses should involve the coordinated partners' modifications resulted in complementary combinations of their genotypes. The research presented in this paper is supported by grants from Russian Foundation of Basic Research (04-04-48457, 06-04-48800, 06-04-89000NWO); NWO Centre of Excellence: 047. 018. 001.
Ecological genetics. 2008;6(2):49-60
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FATE AND ECOLOGICAL INTERACTIONS OF FIREFLY LUC GENE-TAGGED SINORHIZOBIUM MELILOTI 2011-BACTERIA IN SOIL INHABITED BY HIGH LEVELS OF INDIGENOUS ALFALFA NODULATING POPULATIONS
Selbitschka W., Keller M., Dresing U., Dammann-Kalinowski T., Krahn I., Schneiker-Bekel S., Sch?ffer D., Lotz W., Miethling-Graff R., Tebbe,  C.C., P?hler A.
Abstract
A field study was conducted with genetically modified sinorhizobium meliloti strains L1 (RecA-) and L33 (RecA+), both tagged with the firefly luciferase luc gene as an identification marker. The strains' fate was studied over a time period of five years. Both strains were rapidly outcompeted for alfalfa nodulation by an indigenous population. In summary, this study demonstrates the usefulness of tagging bacteria designed for environmental releases by the firefly luciferase gene and the high resilience of soil bacteria to allow the establishment of foreign bacterial populations. This work was supported by grants of the German Federal Ministry of Education and Research (BMBF). We thank Penny Hirsch for valuable discussion concerning the preparation of the peat-based inoculants. The contribution of the Bayer-ische Staatsministerium fur Ernahrung, Landwirtschaft und Forsten for making available the field release site in Stras-smoos is gratefully acknowledged. We thank Rudolf Beck and the team of the Strassmoos experimental plant station for their excellent support during the field study.
Ecological genetics. 2008;6(2):61-71
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