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Microarray Analysis Reveal Global Differential Transcritomes of Mesorhizobium huakuii 7653R between Bacteroids and Free-living Cells

ABSTRACT: Mesorhizobium huakuii 7653R is an α-proteobacterium that occurs either in a nitrogen-fixing symbiosis with its host plant, A. sinicus, or free-living in the soil. Investigation of whole genome gene expression level changes in Bacteroids compared to the free-living cells. Understand how M. huakuii 7653R responds to alterations in its environment and to the physiological changes that occur during bacteroid differentiation.

ORGANISM(S): Mesorhizobium huakuii 7653R

PROVIDER: GSE48090 | GEO | 2014/06/30

SECONDARY ACCESSION(S): PRJNA208945

REPOSITORIES: GEO

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Project description:During the legume-rhizobium symbiosis, free-living soil bacteria known as rhizobia trigger the formation of root nodules. The rhizobia infect these organs and adopt an intracellular lifestyle within the symbiotic nodule cells where they become nitrogen-fixing bacteroids. Several legume lineages enforce their symbionts into an extreme cellular differentiation, comprising cell enlargement and genome endoreduplication. The antimicrobial peptide transporter BclA is a major determinant of this differentiation process in Bradyrhizobium sp. ORS285, a symbiont of Aeschynomene spp.. In the absence of BclA, Bradyrhizobium sp. ORS285 proceeds until the intracellular infection of nodule cells but the bacteria cannot differentiate into enlarged polyploid bacteroids and fix nitrogen. The nodule bacteria of the bclA mutant constitute thus an intermediate stage between the free-living soil bacteria and the intracellular nitrogen-fixing bacteroids. Metabolomics on whole nodules of Aeschynomene afraspera and Aeschynomene indica infected with the ORS285 wild type or the bclA mutant revealed 47 metabolites that differentially accumulated concomitantly with bacteroid differentiation. Bacterial transcriptome analysis of these nodules discriminated nodule-induced genes that are specific to differentiated and nitrogen-fixing bacteroids and others that are activated in the host microenvironment irrespective of bacterial differentiation and nitrogen fixation. These analyses demonstrated that the intracellular settling of the rhizobia in the symbiotic nodule cells is accompanied with a first transcriptome switch involving several hundreds of upregulated and downregulated genes and a second switch accompanying the bacteroid differentiation, involving less genes but that are expressed to extremely elevated levels. The transcriptomes further highlighted the dynamics of oxygen and redox regulation of gene expression during nodule formation and we discovered that bclA represses the expression of non-ribosomal peptide synthetase gene clusters suggesting a non-symbiotic function of BclA. Together, our data uncover the metabolic and gene expression changes that accompany the transition from intracellular bacteria into differentiated nitrogen-fixing bacteroids.

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Microarray Analysis Reveal Global Differential Transcritomes of Mesorhizobium huakuii 7653R between Bacteroids and Free-living Cells

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