Most heat-tolerant rhizobia show high induction of major chaperone genes upon stress

Abstract

The aims of this study were to evaluate the temperature stress tolerance of chickpea rhizobia and to investigate whether tolerance is related to the species or the site of origin of the isolates. Additionally, the molecular bases of temperature stress tolerance in rhizobia were investigated, by comparing the expression of chaperone genes dnaKJ and groESL in thermotolerant and thermosensitive isolates. Tolerance to cold, heat and heat shock was evaluated for 53 mesorhizobia obtained from several provinces of Portugal and assigned to different species. Associations between isolates' tolerance phenotype and several provinces of origin were found. Some species groups were found to differ significantly in their ability to tolerate temperature stress. Analysis of the dnaK and groESL expression by Northern hybridization, using isolates from three species groups, showed an increase in the transcripts levels with heat, but not with cold stress. Interestingly, a higher induction of chaperone genes was detected in heat-tolerant isolates when compared with that of sensitive isolates of the same species. To our knowledge, this is the first analysis of chaperone genes' expression comparing tolerant and sensitive strains. The present study suggests a relationship between higher transcriptional induction of major chaperone genes and higher tolerance to heat in rhizobia.

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

“…15 In Mesorhizobium spp., both dnaK and groESL genes were reported to be transcriptionally induced by a temperature upshift, especially in heat tolerant isolates. 16 In rhizobia, groESL operons are often CIRCE (controlling inverted repeat of chaperone expression) regulated, as already reported in Bradyrhizobium japonicum , S. meliloti and Rhizobium leguminosarum . 13,17,18 CIRCE is a highly conserved DNA sequence that serves as binding site of the repressor protein HrcA.…”

“…Nevertheless, the real-time qRT–PCR results (Table 1) show that dnaK was induced by heat shock, agreeing with previous studies in Mesorhizobium . 16 Approximately, 2-fold induction of the dnaK gene was detected in S. meliloti cells exposed to 40°C for 30 min, 5 while no induction was reported for a shorter heat shock (42°C for 15 min). 27 In the microarray analysis, the changes in expression levels of the dnaK gene were considered not statistically significant due to discrepancies among replicates.…”

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

“…In addition to a main role in de novo folding, DnaK has various other functions, including protein transport [45], and in the increased stability of RNA polymerase σ 32 factor (RpoH), an important component of the heat-shock response in several organisms [46-49]. …”

Tolerance of Mesorhizobium type strains to different environmental stresses

“…As it is known, phenotypes might differ from strain to strain within the same species (Sneath 2001). However, recent studies have shown that isolates from M. ciceri and M. mediterraneum are significantly more tolerant to temperature stress than isolates from other species (Alexandre and Oliveira 2011).…”