Project description:RpoN (σ54) is the key sigma factor for the regulation of transcription of nitrogen fixation genes in diazotrophic bacteria, which include alpha- and beta-rhizobia. Our previous studies showed that a rpoN mutant of the beta-rhizobial strain Paraburkholderia phymatum formed root nodules on Phaseolus vulgaris that were unable to reduce atmospheric nitrogen into ammonia. In an effort to further characterize the RpoN regulon of P. phymatum, transcriptomics was combined with a powerful metabolomics approach. The metabolome of P. vulgaris root nodules infected by the P. phymatum rpoN Fix- mutant revealed statistically significant metabolic changes compared to wild-type Fix+ nodules, including reduced amounts of chorismate and elevated levels of flavonoids. A transcriptome analysis on Fix+ and Fix- nodules – combined with a search for RpoN binding sequences in promoter regions of regulated genes – confirmed the expected control of σ54 on nitrogen fixation genes in nodules. The transcriptomic data also identified additional target genes, whose differential expression was able to explain the observed metabolite changes in a numerous cases. Moreover, the genes encoding the two-component regulatory system NtrBC were downregulated in root nodules induced by the rpoN mutant and contained a putative RpoN binding motif in their promoter region, suggesting direct regulation. The construction and characterization of an ntrB mutant strain revealed impaired nitrogen assimilation in free-living conditions, as well as a noticeable symbiotic phenotype by forming less but heavier nodules on P. vulgaris roots.
Project description:Paraburkholderia phymatum STM815 is a nitrogen-fixing endosymbiont that forms root nodules on the agriculturally important Phaseolus vulgaris and other host plants. We previously showed that the nodules induced by a STM815 mutant of the gene encoding the master regulator of nitrogen fixation NifA showed no nitrogenase activity (Fix-) and increased in number compared to P. vul-garis plants infected with the wild-type strain. To further investigate the role of NifA during symbiosis, nodules from P. phymatum wild-type and nifA mutants were collected and analyzed by metabolomics and dual RNA-Sequencing, allowing us to investigate both host and symbiont transcriptome. Using this approach, several metabolites changes could be assigned to bacterial or plant responses. While the amount of the C4-dicarboxylic acid succinate and of several amino acids was lower in Fix- nodules, the level of indole-acetamide (IAM) and brassinosteroids increased in Fix- nodules. Transcriptome analysis identified P. phymatum genes involved in transport of C4-dicarboxylic acids, carbon metabolism, auxin metabolism and stress response to be differen-tially expressed in absence of NifA. Furthermore, P. vulgaris genes involved in autoregulation of nodulation (AON) are repressed in nodules in absence of NifA potentially explaining the hyper-nodulation phenotype of the nifA mutant. These results and additional validation experiments suggest that P. phymatum STM815 NifA is not only important to control expression of nitrogenase and related enzymes but is also involved in regulating its own auxin production and stress re-sponse. Finally, our data indicate that P. vulgaris does sanction the nifA nodules by depleting the local carbon allocation rather than by mounting a strong systemic immune response to the Fix- rhizobia.
Project description:Paraburkholderia phymatum belongs to the β-subclass of proteobacteria. It has recently been shown to be able to nodulate and fix nitrogen in symbiosis with several mimosoid and papillionoid legumes. In contrast to symbiosis of legumes with α-proteobacteria, very little is known about the molecular determinants underlying the successful establishment of this mutualistic relationship with β-proteobacteria. In this study, we analyzed RNA-seq data of free-living P. phymatum growing under nitrogen replete and limited conditions, the latter partially mimicking the situation in nitrogen deprived soils. Among the genes up-regulated under nitrogen limitation, we found genes involved in exopolysaccharide production and motility, two traits relevant for plant root infection. Next, RNA-seq data of P. phymatum grown under free-living conditions and from symbiotic root nodules of Phaseolus vulgaris (common bean) were generated and compared. Among the genes highly up-regulated during symbiosis, we identified an operon encoding a potential cytochrome o ubiquinol oxidase (Bphy_3646-49). Bean root nodules induced by a cyoB mutant strain showed reduced nitrogenase and nitrogen fixation abilities suggesting an important role of the cytochrome for respiration inside the nodule. Analysis of mutant strains for RNA polymerase transcription factor rpoN (σ54) and its activator NifA indicated that – similar to the situation in α-rhizobia – P. phymatum RpoN and NifA are key regulators during symbiosis with P. vulgaris.
Project description:Background: MiRNAs and phasiRNAs are negative regulators of gene expression. These small RNAs have been extensively studied in plant model species but only 10 mature microRNAs are present in miRBase version 21 and no phasiRNAs have been identified for the legume model Phaseolus vulgaris. Thanks to the recent availability of the first version of the common bean genome, degradome data and small RNA libraries, we are able to present here a catalog of the microRNAs and phasiRNAs of this organism and, particularly, new protagonists of the symbiotic nodulation events. Results: We identified a set of 185 mature miRNAs, including 121 previously unpublished sequences, encoded by 307 precursors and distributed in 98 families. Degradome data allowed us to identify a total of 181 targets for these miRNAs. We reveal two regulatory networks involving conserved miRNAs, known to play crucial roles in the well-establishment of nodules, and novel miRNAs specific of the common bean suggesting a specific action of these sequences. In parallel, we identified 125 loci that potentially produce phased small RNAs and 47 of them present all the characteristics to be triggered by a total of 31 miRNAs, including 14 new miRNAs identified in this study. Conclusions: We provide here a set of new small RNAs, which contribute to the broader scene of the sRNAome of Phaseolus vulgaris. Thanks to the identification of the miRNA targets from degradome analysis and the construction of regulatory networks between the mature microRNAs, we draw up here the probable functional regulation associated with the sRNAome and particularly in N2-fixing symbiotic nodules. Degradome sequencing from Phaseolus vulgaris seedling
Project description:Background: MiRNAs and phasiRNAs are negative regulators of gene expression. These small RNAs have been extensively studied in plant model species but only 10 mature microRNAs are present in miRBase version 21 and no phasiRNAs have been identified for the legume model Phaseolus vulgaris. Thanks to the recent availability of the first version of the common bean genome, degradome data and small RNA libraries, we are able to present here a catalog of the microRNAs and phasiRNAs of this organism and, particularly, new protagonists of the symbiotic nodulation events. Results: We identified a set of 185 mature miRNAs, including 121 previously unpublished sequences, encoded by 307 precursors and distributed in 98 families. Degradome data allowed us to identify a total of 181 targets for these miRNAs. We reveal two regulatory networks involving conserved miRNAs, known to play crucial roles in the well-establishment of nodules, and novel miRNAs specific of the common bean suggesting a specific action of these sequences. In parallel, we identified 125 loci that potentially produce phased small RNAs and 47 of them present all the characteristics to be triggered by a total of 31 miRNAs, including 14 new miRNAs identified in this study. Conclusions: We provide here a set of new small RNAs, which contribute to the broader scene of the sRNAome of Phaseolus vulgaris. Thanks to the identification of the miRNA targets from degradome analysis and the construction of regulatory networks between the mature microRNAs, we draw up here the probable functional regulation associated with the sRNAome and particularly in N2-fixing symbiotic nodules. Small RNA sequencing from 5 Phaseolus vulgaris tissues
Project description:The goal of this study was to detemine the genes responsible of the pod indehiscence in Phaseolus vulgaris by comparing 4 accesions with total, middle and null dehiscence transcriptomes of three stages of pod develoment of Phaseolus vulgaris
Project description:Legumes establish symbiosis with soil rhizobia forming root nodules that fix atmospheric nitrogen. The central role of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in nodule biology has been clearly established. Recently, hydrogen sulfide (H2S) and other reactive sulfur species (RSS) have emerged as novel signaling molecules in animals and plants. A major mechanism by which ROS, RNS, and RSS fulfil their signaling role is the post-translational modification of proteins. To identify possible functions of H2S in nodule development and senescence, we used the tag-switch method to analyze quantitative changes in the persulfidation profile of common bean (Phaseolus vulgaris) nodules at different developmental stages. The proteomic analysis suggests that persulfidation plays a major regulatory role in plant and bacteroid metabolism and senescence. In addition, the effect of a H2S donor on several proteins involved in ROS and RNS homeostasis was investigated. The results obtained using nodule extracts and recombinant proteins suggest a crosstalk between H2S, ROS, and RNS, and a protective function of persulfidation on redox-sensitive enzymes from oxidative modifications that may cause enzyme inactivation. It is concluded that the general decrease of persulfidation levels observed in plant proteins of aging nodules is one of the mechanisms that cause the disruption of redox homeostasis leading to senescence.
Project description:Rhizobium etli is a bacteria that fix nitrogen in symbiotic activity with Phaseolus vulgaris, the common bean plant. In order to accomplish this nitrogen reduction a especial environment is induced in nodules such that gene expression of bacteroid suffer a significant change with respect to its wild type life style. With the purpose to identify genetic alterations between these physiological states, replicates of microarray data were accomplished in similar conditions between bacteria cultivated in free-life (succinate-ammonia) and those carrying on nitrogen fixation inside nodule. Three independent biological materials with one dyeswap were performed.
Project description:A Phaseolus vulgaris genome-wide analysis led to identify the small RNAs (sRNA) of this agronomical important legume. It revealed newly identified P. vulgaris-specific microRNAs (miRNAs) that could be involved in the regulation of the rhizobia-symbiotic process. Generally, novel miRNAs are difficult to identify and study because they are very lowly expressed in a tissue- or cell-specific manner. We aimed to analyze sRNAs from common bean root hairs (RH), a single-cell model, induced with pure Rhizobium etli-Nod factors (NF), a unique type of signal molecule. The sequence analysis of samples from NF-induced and control libraries led to identify 132 mature miRNAs, including 63 novel miRNAs and 1984 phasiRNAs. From these, six miRNAs were significantly differentially expressed during NF-induction, including one novel miRNA: miR-RH82. A parallel degradome analysis of the same samples revealed 29 targets potentially cleaved by novel miRNAs specifically in NF-induced RH samples, however these novel miRNAs were not differentially accumulated in this tissue. This study reveals Phaseolus vulgaris-specific novel miRNA candidates and their corresponding targets that meet all criteria to be involved in the regulation of the early nodulation events.