IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Title Determination of optimal phosphorus concentrations which enhance the establishment of both mycorrhizal and rhizobial symbiosis Authors Manijeh Mohammadi-Dehcheshmeh, Sally E Smith, Steve D. Tyerman Poster Board Number 11 and Brent N Kaiser School of Agriculture, Food and Wine, Waite Campus, University of Adelaide Legume growth and yield productivity is influenced through symbiotic interactions with both rhizobial bacteria and mycorrhizal fungi. Symbiosis with Rhizobium sp. enables access to atmospherically reduced N2, through nitrogen fixation, while the mycorrhizal symbiosis strongly enhances mineral uptake especially phosphorus (P) and zinc(1). P is an essential nutrient required for plant growth. The availability of P in the soil and internally within the plant has been shown to have a contrasting influence on the impact of either the rhizobial or mycorrhizal symbiosis (2-5). At high levels of available plant P, symbiotic nitrogen fixation is enhanced while high concentrations of P can hinder mycorrhizal colonization. The impact of P on either nodulation or mycorrhizal colonization has been studied widely, however little information is available on how P affectsthe interactions between the two symbiosis. In this study, we examined the effects of different concentrations of soil P on both the rhizobial and mycorrhizal symbiosis in soybean. At high P, mycorrhizal colonization (percent root length) decreased while nodule development increased. At low P the opposite response occurred. We are currently evaluating the combined symbiotic response to P in order to identify P concentration ranges that satisfy the needs of both symbiosis. This work will be discussed in the context of maximizing P efficiency under symbiotic conditions and the competing symbiotic relationships regulating P availability. 1. S. E. Smith, F. A. Smith, Annual Review of Plant Biology 62, 227 (2011). 2. D. W. Israel, Plant Physiology 84, 835 (1987). 3. M. Chaudhary et al., Acta Physiologiae Plantarum 30, 537 (2008). 4. J. A. Menge, D. Steirle, D. J. Bagyaraj, E. L. V. Johnson, R. T. Leonard, New Phytologist 80, 575 (1978). 5. P. G. Braunberger, M. H. Miller, R. L. Peterson, New Phytologist 119, 107 (1991). 126 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Title Comparative analysis of genome sequences of Rhizobium galegae HAMBI 540 and HAMBI 1141 Authors Janina Österman 1,3 , Lars Paulin 2 , Edward Alatalo 2 , J. Peter W. Young 3 , Kristina Lindström 1 Poster Board Number 12 1 Department of Food and Environmental Sciences and 2 Institute of Biotechnology, University of Helsinki 3 Department of Biology, University of York Rhizobium galegae (Lindström 1989) is taxonomically distinct and known for its strict host specificity both regarding nodulation and nitrogen fixation. Our aim is to gain insight into molecular mechanisms behind the specificity of nitrogen fixation. As a first step towards this goal we have performed whole genome sequencing of R. galegae symbiovar orientalis strain HAMBI 540 (effective on Galega orientalis) and R. galegae symbiovar officinalis strain HAMBI 1141 (effective on G. officinalis). The draft assembly indicates that both genomes are about 6.4 Mb in size. Preliminary comparison of the genomes has been performed, with a more specific comparison of the symbiotic gene regions of the two strains. Although the two genomes are of approximately the same size, there are important genetic differences between the strains. The most obvious difference is that the HAMBI 1141 genome harbours three replicons, while the corresponding number in HAMBI 540 is two. Furthermore, HAMBI 1141 harbours conjugal transfer systems not present in HAMBI 540. The genes present in the symbiotic regions are the same except for one gene, rpoN, the function of which will be further studied. Annotation of the symbiotic region also led us to the identification of a candidate gene for acetylation of the penultimate N-acetylglucosamine in the R. galegae Nod factor. Differences detected in the comparative analyses will be discussed. 127 2011
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INVENTING THE FUTURE IN INOCULANTS
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