Atypical features of a Ure2p glutathione transferase from Phanerochaete chrysosporium

Abstract

Glutathione transferases (GSTs) are known to transfer glutathione onto small hydrophobic molecules in detoxification reactions. The GST Ure2pB1 from Phanerochaete chrysosporium exhibits atypical features, i.e. the presence of two glutathione binding sites and a high affinity towards oxidized glutathione. Moreover, PcUre2pB1 is able to efficiently deglutathionylate GS-phenacylacetophenone. Catalysis is not mediated by the cysteines of the protein but rather by the one of glutathione and an asparagine residue plays a key role in glutathione stabilization. Interestingly PcUre2pB1 interacts in vitro with a GST of the omega class. These properties are discussed in the physiological context of wood degrading fungi.

Two Sinorhizobium meliloti glutaredoxins regulate iron metabolism and symbiotic bacteroid differentiation
Sofiane M BENYAMINA, Fabien BALDACCI-CRESP, Jeremy COUTURIER, Kamel CHIBANI, Julie HOPKINS, Abdelkader BEKKI, Philippe DE LAJUDIE, Nicolas ROUHIER, Jean-Pierre JACQUOT, Genevieve ALLOING, Alain PUPPO, Pierre FRENDO
Environmental microbiology 15 (3), 795-810

Abstract

Legumes interact symbiotically with bacteria of the Rhizobiaceae to form nitrogen-fixing root nodules. We investigated the contribution of the three glutaredoxin (Grx)-encoding genes present in the Sinorhizobium meliloti genome to this symbiosis. SmGRX1 (CGYC active site) and SmGRX3 (CPYG) recombinant proteins displayed deglutathionylation activity in the 2-hydroethyldisulfide assay, whereas SmGRX2 (CGFS) did not. Mutation of SmGRX3 did not affect S. meliloti growth or symbiotic capacities. In contrast, SmGRX1 and SmGRX2 mutations decreased the growth of free-living bacteria and the nitrogen fixation capacity of bacteroids. Mutation of SmGRX1 led to nodule abortion and an absence of bacteroid differentiation, whereas SmGRX2 mutation decreased nodule development without modifying bacteroid development. The higher sensitivity of the Smgrx1 mutant strain as compared with wild-type strain to oxidative stress was associated with larger amounts of glutathionylated proteins. The Smgrx2 mutant strain displayed significantly lower levels of activity than the wild type for two iron-sulfur-containing enzymes, aconitase and succinate dehydrogenase. This lower level of activity could be associated with deregulation of the transcriptional activity of the RirA iron regulator and higher intracellular iron content. Thus, two S. meliloti Grx proteins are essential for symbiotic nitrogen fixation, playing independent roles in bacterial differentiation and the regulation of iron metabolism.

Genome-wide survey of repetitive DNA elements in the button mushroom Agaricus bisporus
M Foulongne-Oriol, C Murat, R Castanera, L Ramírez, ASM Sonnenberg
Fungal Genetics and Biology

Abstract

Repetitive DNA elements are ubiquitous constituents of eukaryotic genomes. The biological roles of these repetitive elements, supposed to impact genome organization and evolution, are not completely elucidated yet. The availability of whole genome sequence offers the opportunity to draw a picture of the genome-wide distribution of these elements and provide insights into potential mechanisms of genome plasticity. The present study uses in silico approaches to describe tandem repeats and transposable elements distribution in the genome of the button mushroom, Agaricus bisporus. Transposable elements comprised 12.43% of the assembled genome, and 66% of them were found clustered in the centromeric or telomeric regions. Methylation of retrotransposon has been demonstrated. A total of 1996 mini-, 4062 micro-, and 37 satellites motifs were identified. The microsatellites appeared widely and evenly spread over the whole genome sequence, whereas the minisatellites were not randomly distributed. Indeed, minisatellites were found to be associated with transposable elements clusters. Telomeres exhibited a specific sequence with a T_nAG_nsignature. A comparison between the two available genome sequences of A. bisporus was also performed and sheds light on the genetic divergence between the two varieties. Beyond their role in genome structure, repeats provide a virtually endless source of molecular markers useful for genetic studies in this cultivated species.

Optimization of a real-time PCR assay for the detection of the quarantine pathogen< i> Melampsora medusae</i> f. sp.< i> deltoidae</i>
AL Boutigny, C Guinet, A Vialle, R Hamelin, A Andrieux, P Frey, C Husson, R Ioos
Fungal Biology

Melampsora medusae, one of the causal agents of poplar rust, is classified as an A2 quarantine pest for EPPO and its presence in Europe is strictly controlled. Two formae speciales have been described within M. medusae, M. medusae f. sp. deltoidae and M. medusae f. sp. tremuloidae on the basis of their pathogenicity on Populus species from the section Aigeiros (e.g. Populus deltoides) or Populus (e.g. Populus tremuloides), respectively. In this study, a real-time PCR assay was developed allowing the detection of M. medusae f. sp.deltoidae, the forma specialis that is economically harmful. A set of primers and hydrolysis probe was designed based on sequence polymorphisms in the large ribosomal RNA subunit (28S). The real-time PCR assay was optimized and performance criteria of the detection method, i.e. sensitivity, specificity, repeatability, reproducibility and robustness, were assessed. The real-time PCR method was highly specific and sensitive and allowed the detection of one single urediniospore of M. medusae f. sp. deltoidae in a mixture of 2 mg of urediniospores of other Melampsora species. This test offers improved specificity over currently existing conventional PCR tests and can be used for specific surveys in European nurseries and phytosanitary controls, in order to avoid introduction and spread of this pathogen in Europe.

Keywords

• Melampsora;
• poplar rust;
• real-time PCR;
• quarantine pathogen

An improved method compatible with metagenomic analyses to extract genomic DNA from soils in Tuber melanosporum orchards
S Antony‐Babu, C Murat, A Deveau, F Tacon, P Frey‐Klett, S Uroz
Journal of Applied Microbiology

Keywords:

DNA extraction; Soil; Tuber melanosporum ; Calcareous soil