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Affy_med_2011_06-Analysis of the Medicago noot mutant

ABSTRACT: affy_med_2011_06 - affy_med_2011_06 - Legume plants establish a symbiotic interaction with soil bacteria called rhizobia. A complex molecular dialogue between the two partners is necessary for the successful infection and organogenesis processes that will ultimately result in the formation of a nitrogen fixing nodule. During a M. truncatula Tnt1 mutant screen, a new class of symbiotic mutant called noot (nodule root) was identified. This original single recessive mutant develops a root in apical position of nodules that are colonized by bacteria and functional for nitrogen fixation. This conversion suggests that the legume nodule morphogenetic pathway may be derived from a root program. We cloned the NOOT gene and showed that it corresponds to Pisum sativum COCH (Ferguson and Reid, 2005, Plant Cell Physiol 46, 1583-1589). The goal of this project is to compare the transcriptomes from wild type nodules and roots to the noot nodule one. This will allow us to unravel the similarity and differences between the wild type and mutant nodule transcriptomes but also to know which developmental pathway is under the control of the NOOT gene. --Seeds of the WT and noot mutant lines (two mutant alleles: Tnk507 and NF2717) were surface sterilized and placed at 4°C for three days on a minimal BNM medium square plate (12cm X 12cm). Seeds were germinated at room temperature and 10 seeds were placed in a row on nitrogen poor (BNM) plate. Seedlings were inoculated using Sinorhizobium meliloti Rm41 for nodule production. Some WT plants were not infected by the bacteria in order to collect roots. Nodules and roots were harvested 18 to 21 days post inoculation. Each experimental repetition (3 WT nodules, 3 WT roots and 2 mutant nodules of each allele) was harvested at a separated day. RNA preparations were done using a Quiagen Kit.

ORGANISM(S): Medicago sativa Sinorhizobium meliloti Medicago truncatula

PROVIDER: GSE36558 | GEO | 2012/06/01

SECONDARY ACCESSION(S): PRJNA153435

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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Affy_med_2011_06-Analysis of the Medicago noot mutant

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