Project description:BackgroundThe symbiotic phenotype of Neorhizobium galegae, with strains specifically fixing nitrogen with either Galega orientalis or G. officinalis, has made it a target in research on determinants of host specificity in nitrogen fixation. The genomic differences between representative strains of the two symbiovars are, however, relatively small. This introduced a need for a dataset representing a larger bacterial population in order to make better conclusions on characteristics typical for a subset of the species. In this study, we produced draft genomes of eight strains of N. galegae having different symbiotic phenotypes, both with regard to host specificity and nitrogen fixation efficiency. These genomes were analysed together with the previously published complete genomes of N. galegae strains HAMBI 540T and HAMBI 1141.ResultsThe results showed that the presence of an additional rpoN sigma factor gene in the symbiosis gene region is a characteristic specific to symbiovar orientalis, required for nitrogen fixation. Also the nifQ gene was shown to be crucial for functional symbiosis in both symbiovars. Genome-wide analyses identified additional genes characteristic of strains of the same symbiovar and of strains having similar plant growth promoting properties on Galega orientalis. Many of these genes are involved in transcriptional regulation or in metabolic functions.ConclusionsThe results of this study confirm that the only symbiosis-related gene that is present in one symbiovar of N. galegae but not in the other is an rpoN gene. The specific function of this gene remains to be determined, however. New genes that were identified as specific for strains of one symbiovar may be involved in determining host specificity, while others are defined as potential determinant genes for differences in efficiency of nitrogen fixation.
Project description:BACKGROUND: The species Neorhizobium galegae comprises two symbiovars that induce nodules on Galega plants. Strains of both symbiovars, orientalis and officinalis, induce nodules on the same plant species, but fix nitrogen only in their own host species. The mechanism behind this strict host specificity is not yet known. In this study, genome sequences of representatives of the two symbiovars were produced, providing new material for studying properties of N. galegae, with a special interest in genomic differences that may play a role in host specificity. RESULTS: The genome sequences confirmed that the two representative strains are much alike at a whole-genome level. Analysis of orthologous genes showed that N. galegae has a higher number of orthologs shared with Rhizobium than with Agrobacterium. The symbiosis plasmid of strain HAMBI 1141 was shown to transfer by conjugation under optimal conditions. In addition, both sequenced strains have an acetyltransferase gene which was shown to modify the Nod factor on the residue adjacent to the non-reducing-terminal residue. The working hypothesis that this gene is of major importance in directing host specificity of N. galegae could not, however, be confirmed. CONCLUSIONS: Strains of N. galegae have many genes differentiating them from strains of Agrobacterium, Rhizobium and Sinorhizobium. However, the mechanism behind their ecological difference is not evident. Although the final determinant for the strict host specificity of N. galegae remains to be identified, the gene responsible for the species-specific acetylation of the Nod factors was identified in this study. We propose the name noeT for this gene to reflect its role in symbiosis.
Project description:Medicago truncatula engages in root nodule symbiosis by developing a de novo plant organ (known as nodule) in its roots in response to the infection by rhizobia. These nodules are de novo plant organs that provide an optimal environment for the rhizobia to fix nitrogen in exchange for photosynthates. The establishment of root nodule symbioses (RNS) requires the coordination of two distinct processes: bacterial infection and nodule organogenesis. In this study we used single-cell RNA-seq to investigate the first hours of the establishment of the root nodule symbiosis aiming to identify the transcriptional mechanisms governing this process.
Project description:The toxic legume plant, Galega officinalis, is native to the Eastern Mediterranean and Black Sea regions. This legume is considered to be a noxious weed, and its establishment in Canada may have resulted from ornamental planting and/or field trials. In its native range, a highly specific nitrogen-fixing symbiosis with the bacterium, Neorhizobium galegae symbiovar (sv.) officinalis, is required for normal growth. In North America, nothing is known about the bacterial symbionts of G. officinalis. Our purpose was to determine the species and symbiovar identity of symbiotic bacteria associated with invasive plants of G. officinalis at five sites in the province of Ontario, Canada. Sequence analysis of four housekeeping (16S rRNA, atpD, glnII, and recA) and two symbiosis (nodC and nifH) genes showed that all 50 bacterial isolates from root nodules of G. officinalis at the five Canadian sites were identical to strains of N. galegae sv. officinalis originating either from Europe or the Caucasus. Plant tests indicated that soils collected from four Canadian sites without a history of agriculture or presence of G. officinalis were deficient in symbiotic bacteria capable of eliciting nodules on this plant. Collectively our data support the hypothesis of anthropogenic co-introduction of G. officinalis and its specific symbiotic bacterium into Canada from the Old World. Factors that may limit the spread of G. officinalis in new environments are discussed.
Project description:Legumes interact with nodulating bacteria that convert atmospheric nitrogen into ammonia for plant use. This nitrogen fixation takes place within root nodules that form after infection of root hairs by compatible rhizobia. Using cDNA microarrays, we monitored gene expression in soybean (Glycine max) inoculated with the nodulating bacterium Bradyrhizobium japonicum 4, 8, and 16 days after inoculation (dai), time points that coincided with nodule development and the onset of nitrogen fixation. This experiment identified several thousand genes that were differentially expressed in response to B. japonicum inoculation. Expression of 27 genes was analyzed by qRT-PCR and their expression patterns mimicked the microarray results confirming integrity of analyses. The microarray results suggest that B. japonicum reduces plant defense responses during nodule development. In addition, the data revealed a high level of regulatory complexity (transcriptional, post-transcriptional, translational, post-translational) that is likely essential for development of the symbiosis and adjustment to an altered nutritional status. Keywords = symbiosis Keywords = nodulation Keywords = rhizobium Keywords = defense Keywords = ANOVA Keywords = plant loop design, 7 samples, 7 comparison, 2 technical repeats including dye swaps, 4 biological repeats
Project description:Legumes interact with nodulating bacteria that convert atmospheric nitrogen into ammonia for plant use. This nitrogen fixation takes place within root nodules that form after infection of root hairs by compatible rhizobia. Using cDNA microarrays, we monitored gene expression in soybean (Glycine max) inoculated with the nodulating bacterium Bradyrhizobium japonicum 4, 8, and 16 days after inoculation (dai), time points that coincided with nodule development and the onset of nitrogen fixation. This experiment identified several thousand genes that were differentially expressed in response to B. japonicum inoculation. Expression of 27 genes was analyzed by qRT-PCR and their expression patterns mimicked the microarray results confirming integrity of analyses. The microarray results suggest that B. japonicum reduces plant defense responses during nodule development. In addition, the data revealed a high level of regulatory complexity (transcriptional, post-transcriptional, translational, post-translational) that is likely essential for development of the symbiosis and adjustment to an altered nutritional status. Keywords = symbiosis Keywords = nodulation Keywords = rhizobium Keywords = defense Keywords = ANOVA Keywords = plant Keywords: nodulating vs not nodulating