Project description:To examine how the Arabidopsis root development responds to the Rhizobium sp. IRBG74 treatment at the molecular level, we performed RNA-seq experiments. Our RNA-seq results suggest that expression of genes mainly involved in auxin signaling, cell wall and cell membrane integrity and transport is altered in response to colonization by Rhizobium sp. IRBG74.
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.
Project description:We studied potentially amyloidogenic proteins (e.g. protein forming polymers and complexes that are resistant to treatment with ionic detergents) in root nodules formed by two lines of garden pea (P. sativum L.): Sprint-2 (Fix+ phenotype) and Sprint-2Fix- (sym31) (Fix- phenotype) inoculated with the Rhizobium leguminosarum bv. viciae RCAM1026 root nodule bacteria. The Fix+ phenotype is characterized by effective (ability to fix nitrogen) root nodules formation. The Fix- line is a descendant of the Fix+ line and forms ineffective root nodules (unable to fix nitrogen) with undifferentiated bacteroids. We demonstrated the presence of both plant and bacterial proteins in detergent resistant fractions, including previously identified amyloid proteins RopA and RopB of R. leguminosarum and vicilin of P. sativum L.
Project description:Coevolutionary change requires reciprocal selection between interacting species, i.e., that the partner genotypes that are favored in one species depend on the genetic composition of the interacting species. Coevolutionary genetic variation is manifested as genotype ´ genotype (G ´ G) interactions for fitness from interspecific interactions. Although quantitative genetic approaches have revealed abundant evidence for G ´ G interactions in symbioses, the molecular basis of this variation remains unclear. Here we study the molecular basis of G ´ G interactions in a model legume-rhizobium mutualism using gene expression microarrays. We find that, like quantitative traits such as fitness, variation in the symbiotic transcriptome may be partitioned into additive and interactive genetic components. Our results suggest that plant genetic variation is the largest influence on nodule gene expression, and that plant genotype and the plant genotype ´ rhizobium genotype interaction determine global shifts in rhizobium gene expression that in turn feedback to influence plant fitness benefits. Moreover, the transcriptomic variation we uncover implicates regulatory changes in both species as drivers of symbiotic gene expression variation. Our study is the first to partition genetic variation in a symbiotic transcriptome, and illuminates potential molecular routes of coevolutionary change. We assayed gene expression using three biological replicates for each plant genotype × rhizobium genotype combination (4 combinations) for a total of 12 chips.
Project description:Coevolutionary change requires reciprocal selection between interacting species, i.e., that the partner genotypes that are favored in one species depend on the genetic composition of the interacting species. Coevolutionary genetic variation is manifested as genotype ´ genotype (G ´ G) interactions for fitness from interspecific interactions. Although quantitative genetic approaches have revealed abundant evidence for G ´ G interactions in symbioses, the molecular basis of this variation remains unclear. Here we study the molecular basis of G ´ G interactions in a model legume-rhizobium mutualism using gene expression microarrays. We find that, like quantitative traits such as fitness, variation in the symbiotic transcriptome may be partitioned into additive and interactive genetic components. Our results suggest that plant genetic variation is the largest influence on nodule gene expression, and that plant genotype and the plant genotype ´ rhizobium genotype interaction determine global shifts in rhizobium gene expression that in turn feedback to influence plant fitness benefits. Moreover, the transcriptomic variation we uncover implicates regulatory changes in both species as drivers of symbiotic gene expression variation. Our study is the first to partition genetic variation in a symbiotic transcriptome, and illuminates potential molecular routes of coevolutionary change. We assayed gene expression using three biological replicates for each plant genotype × rhizobium genotype combination (4 combinations) for a total of 12 chips. We compared gene expression in each of four combinations of Medicago truncatula families and Sinorhizobium meliloti strains using Affymetrix Medicago GeneChips to study how the entire transcriptome and individual genes responded to differences between plant families, between rhizobium strains, and due to the plant family × rhizobium strain (G × G) interaction.