Proteomic profiling of Rhizobium tropiciPRF 81: identification of conserved and specific responses to heat stress

Abstract

BackgroundRhizobium tropici strain PRF 81 (= SEMIA 4080) has been used in commercial inoculants for application to common-bean crops in Brazil since 1998, due to its high efficiency in fixing nitrogen, competitiveness against indigenous rhizobial populations and capacity to adapt to stressful tropical conditions, representing a key alternative to application of N-fertilizers. The objective of our study was to obtain an overview of adaptive responses to heat stress of strain PRF 81, by analyzing differentially expressed proteins when the bacterium is grown at 28°C and 35°C.ResultsTwo-dimensional gel electrophoresis (2DE) revealed up-regulation of fifty-nine spots that were identified by MALDI-TOF/TOF-TOF. Differentially expressed proteins were associated with the functional COG categories of metabolism, cellular processes and signaling, information storage and processing. Among the up-regulated proteins, we found some related to conserved heat responses, such as molecular chaperones DnaK and GroEL, and other related proteins, such as translation factors EF-Tu, EF-G, EF-Ts and IF2. Interestingly, several oxidative stress-responsive proteins were also up-regulated, and these results reveal the diversity of adaptation mechanisms presented by this thermotolerant strain, suggesting a cross-talk between heat and oxidative stresses.ConclusionsOur data provide valuable protein-expression information relevant to the ongoing genome sequencing of strain PRF 81, and contributes to our still-poor knowledge of the molecular determinants of the thermotolerance exhibited by R. tropici species.

Genomic basis of broad host range and environmental adaptability of Rhizobium tropici CIAT 899 and Rhizobium sp. PRF 81 which are used in inoculants for common bean (Phaseolus vulgaris L.)

“…Other common components of the heat-shock response such as the Clp and Lon protease systems, and the translation elongation factor LepA were also found in the CIAT 899 and PRF 81 genomes. The differential expression of several PRF 81 proteins under high-temperature stress such as DnaK, GroEL, and the translation factors EF-Tu, Ef-G and IF2, was recently demonstrated [184]. It is noteworthy that some HSPs also play protective roles during other stressful conditions like the DnaK machinery during hyperosmotic salt stress [185] and HtrA in oxidative damage [183].…”

“…Such overlap or cross-talk between the stress responses is not uncommon. We have recently found that the expression of several oxidative stress-related proteins of PRF 81 is up-regulated after exposure to high temperatures [184]. …”

Temperature sensitivity of food legumes: a physiological insight

“…Tolerant strains of Mesorhizobium, when exposed to heat shock, had increased GroEL (HSP60) gene expression (HSP60) is an HSP that acts as a chaperone and also regulates nif gene (Ribbe and Burgess 2001;Horwich and Fenton 2009). The proteome profiling of Rhizobium tropici strain PRF81 grown at 28 and 35°C revealed up-regulation of about 59 different proteins under heat stress including HSPs such as DnaK and GroEL, along with various anti-oxidative proteins indicating some cross-talk between heat and oxidative stresses (Gomes et al 2012). On the other hand, some additional studies have contradicted the positive correlation between temperature tolerance and symbiotic nitrogen fixation where either no correlation was observed, as reported in Acacia nilotica (Rustogi et al 1996), Bradyrhizobium and Rhizobium (Gopalakrishnan and Dudeja 1999) or a negative correlation was reported, as observed in lentil (Moawad and Beck 1991).…”

Global Transcriptional Response to Heat Shock of the Legume Symbiont Mesorhizobium loti MAFF303099 Comprises Extensive Gene Downregulation

“…21–23 Regarding the co-chaperone dnaJ , rhizobia mutants showed that both stress tolerance and symbiotic performance are affected. 21,22,24 …”