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

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).
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