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 Session Details: Thursday 1 December 2011 Concurrent Session 17 – Molecular Characterization of N-fixing organisms 1100 - 1230 Authors: Ana Alexandre 1,2 Solange Oliveira 1 1 ICAAM - Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Universidade de Évora, 7002-554 Évora Portugal. 2 IIFA - Instituto de Investigação e Formação Avançada, Universidade de Évora, 7002- 554 Évora, Portugal. Presentation Title: Major chaperone genes are highly induced in heat-tolerant rhizobia Presentation Time: 1100 – 1120 The demand for more effective utilization of biologically-fixed N in agricultural systems has prompted studies on rhizobia tolerance to abiotic factors. Rhizobia ability to endure environmental stresses, such as soil pH, salinity and temperature is particularly important in legume-rhizobia symbioses under suboptimal conditions. The present work aimed at evaluating the temperature stress tolerance of native chickpea rhizobia and investigating if tolerance is related to isolates„ species or origin site. Another aim was to investigate the molecular bases of temperature stress tolerance, by comparing the expression levels of major chaperone genes, in thermotolerant and thermosensitive isolates. A set of 53 chickpea mesorhizobia, previously isolated from several provinces of Portugal and characterized in terms of symbiotic effectiveness, plasmid profiles and species affiliation, was used (Alexandre et al 2009). Temperature stress tolerance was evaluated under cold, heat and heat shock conditions. Mesorhizobia showed high diversity in their ability to grow under temperature stress; nevertheless most isolates tolerate heat shock or cold stress better than continuous heat. Distinct species groups were found to differ significantly in their ability to tolerate temperature stress. An association was found between some provinces of origin and stress tolerance of the isolates. In order to study the molecular bases of temperature stress tolerance, the mRNA levels of chaperone genes were analysed upon stress, using tolerant and sensitive chickpea rhizobia. Analysis of dnaK and groESL genes expression by northern hybridisation, using isolates from several species groups, showed an increase in the transcripts levels with heat but not with cold stress. Interestingly, following temperature upshifts, the induction of chaperone genes was higher in tolerant than in sensitive isolates from the same species (Alexandre & Oliveira, 2011). Overall, these results suggest that higher transcriptional induction of the major chaperone genes could be related with a higher tolerance to heat in rhizobia. Alexandre A, Brígido C, Laranjo M, Rodrigues S & Oliveira S (2009). Survey of chickpea rhizobia diversity in Portugal reveals the predominance of species distinct from Mesorhizobium ciceri and Mesorhizobium mediterraneum. Microb Ecol 58: 930-841. Alexandre A & Oliveira S (2011). Most heat-tolerant rhizobia show high induction of major chaperone genes upon stress. FEMS Microbiol Ecol 75: 28-36. This work was supported by Fundação para a Ciência e Tecnologia: project FCOMP-01-0124-FEDER-007091 and fellowship to A. A. (SFRH/BPD/73243/2010). 104 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Thursday 1 December 2011 Concurrent Session 17 – Molecular Characterization of N-fixing organisms 1100 - 1230 Authors: Nazalan Najimudin 1 , Hok-Chai Yam 1 , Mohd-Razip Samian 1 and Suriani Mohamad 1 1 School of Biological Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia. Presentation Title: Characterization of nitrogen fixation genes from Paenibacillus polymyxa ATCC 15970 Presentation Time: 1120 – 1140 Paenibacilus polymyxa ATCC 15970 is a Gram positive bacterium capable of converting dinitrogen (N2) to ammonia. The nitrogen fixation operon of this strain was determined to have the gene arrangement of nifBHDK. The deduced NifBHDK amino acid sequences were 499 aa, 255 aa, 482 aa and 509 aa, respectively. The putative nifD and nifK ORFs were overlapping by 4 nucleotides. The transcriptional start sites of nifB and nifH were determined by cRACE and cmRACE methods. Two different transcriptional start sites were obtained - upstream of nifB and another upstream of nifH. Therefore, the nifH gene could possibly be expressed from two different mRNA molecules transcribed from two different promoters located upstream of nifB and nifH, respectively. Based on their transcriptional start sites, the promoter regions of nifB and nifH revealed consensus sequences that were distinguishable from the traditional nif promoter. This suggested that the expression of nif genes in P. polymyxa was possibly controlled by a unique regulation system. The nifB gene is possibly coexpressed with the structural genes nifHDK. The promoter sequences of nifB and nifH were different from the typical nif promoter motif. Two highly consensus sequences were found at the presumptive promoter regions of nifB and nifH located roughly at positions -8 (GTAAGGG) and -28 (AGACAAA) with respect to their transcriptional start sites. This novel promoter motif merits future investigation. 105 2011
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