Evidence of gene flow between sympatric populations of the Middle East‐Asia Minor 1 and Mediterranean putative species of Bemisia tabaci

A Tahiri, F Halkett, M Granier, G Gueguen, M Peterschmitt

Ecology and Evolution

Summary

Bemisia tabaci is a complex of putative species that exhibit a strong geographical pattern. Crossing experiments have revealed various degrees of reproductive isolation between these nascent species, ranging between fertile first-generation hybrids (F1) and no F1 at all. However, the relevance of these results under natural conditions is generally not known. The worldwide invasion of the putative species Middle East-Asia Minor 1 (MEAM1) has caused secondary contacts between allopatric species, which in turn provide an opportunity to detect potential hybrids in nature. A total of 346 female B. tabaci were collected in 2003 and 2005 in the North East of Morocco and assigned to MEAM1 (119), Mediterranean (Med) (225) and a new putative species (2) using mitochondrial cytochrome oxidase (mtCOI) gene sequences. MEAM1 and Med individuals were characterized at seven microsatellite loci. MEAM1 and Med were found to be sympatric in 11 of 12 samples (6 fields/year). As previously reported from Spain, MEAM1 frequency decreased over time. The genetic data are consistent with a recent introduction of MEAM1. A Bayesian clustering analysis (structure) distinguished two groups, which were 100% consistent with the mtCOI groups. From several lines of evidence, two individuals were identified as hybrids. Assignment profiles using newhybrids and allele composition indicated that they were not F1 hybrids. The results are discussed in relation to the secondary endosymbiont infection status determined on a sample of individuals, and the contrasting outcomes of the reported crossing experiments between MEAM1 and Med.

Community genetics in the time of next‐generation molecular technologies
F Gugerli, R Brandl, B Castagneyrol, A Franc, H Jactel, HP Koelewijn, F …
Molecular Ecology 22 (12), 3198-3207

Summary

Understanding the interactions of co-occurring species within and across trophic levels provides key information needed for understanding the ecological and evolutionary processes that underlie biological diversity. As genetics has only recently been integrated into the study of community-level interactions, the time is right for a critical evaluation of potential new, gene-based approaches to studying communities. Next-generation molecular techniques, used in parallel with field-based observations and manipulative experiments across spatio-temporal gradients, are key to expanding our understanding of community-level processes. Here, we introduce a variety of ‘-omics’ tools, with recent studies of plant–insect herbivores and of ectomycorrhizal systems providing detailed examples of how next-generation approaches can revolutionize our understanding of interspecific interactions. We suggest ways that novel technologies may convert community genetics from a field that relies on correlative inference to one that reveals causal mechanisms of genetic co-variation and adaptations within communities.

Microbe-independent entry of oomycete RxLR effectors and fungal RxLR-like effectors into plant and animal cells is specific and reproducible
BM Tyler, SD Kale, Q Wang, K Tao, HR Clark, K Drews, V Antignani, A Rumore …
Molecular Plant-Microbe Interactions 26 (6), 611-616

Summary

A wide diversity of pathogens and mutualists of plant and animal hosts, including oomycetes and fungi, produce effector proteins that enter the cytoplasm of host cells. A major question has been whether or not entry by these effectors can occur independently of the microbe or requires machinery provided by the microbe. Numerous publications have documented that oomycete RxLR effectors and fungal RxLR-like effectors can enter plant and animal cells independent of the microbe. A recent reexamination of whether the RxLR domain of oomycete RxLR effectors is sufficient for microbe-independent entry into host cells concluded that the RxLR domains of Phytophthora infestans Avr3a and of P. sojae Avr1b alone are NOT sufficient to enable microbe-independent entry of proteins into host and nonhost plant and animal cells. Here, we present new, more detailed data that unambiguously demonstrate that the RxLR domain of Avr1b does show efficient and specific entry into soybean root cells and also into wheat leaf cells, at levels well above background nonspecific entry. We also summarize host cell entry experiments with a wide diversity of oomycete and fungal effectors with RxLR or RxLR-like motifs that have been independently carried out by the seven different labs that coauthored this letter. Finally we discuss possible technical reasons why specific cell entry may have been not detected by Wawra et al. (2013).

The iron-sulfur cluster assembly machineries in plants: current knowledge and open questions

J Couturier, B Touraine, JF Briat, F Gaymard, N Rouhier Frontiers in Plant Science 4, 259

Many metabolic pathways and cellular processes occurring in most sub-cellular compartments depend on the functioning of iron-sulfur (Fe-S) proteins, whose cofactors are assembled through dedicated protein machineries. Recent advances have been made in the knowledge of the functions of individual components through a combination of genetic, biochemical and structural approaches, primarily in prokaryotes and non-plant eukaryotes. Whereas most of the components of these machineries are conserved between kingdoms, their complexity is likely increased in plants owing to the presence of additional assembly proteins and to the existence of expanded families for several assembly proteins. This review focuses on the new actors discovered in the past few years, such as glutaredoxin, BOLA and NEET proteins as well as MIP18, MMS19, TAH18, DRE2 for the cytosolic machinery, which are integrated into a model for the plant Fe-S cluster biogenesis systems. It also discusses a few issues  currently subjected to an intense debate such as the role of the mitochondrial frataxin and of glutaredoxins, the functional separation between scaffold, carrier and iron-delivery proteins and the crosstalk existing between different organelles.

Carbon Transfer from the Host to Tuber melanosporum Mycorrhizas and Ascocarps Followed Using a 13C Pulse-Labeling Technique
F Le Tacon, B Zeller, C Plain, C Hossann, C Bréchet, C Robin
PloS one 8 (5), e64626

Abstract

Truffles ascocarps need carbon to grow, but it is not known whether this carbon comes directly from the tree (heterotrophy) or from soil organic matter (saprotrophy). The objective of this work was to investigate the heterotrophic side of the ascocarp nutrition by assessing the allocation of carbon by the host to Tuber melanosporum mycorrhizas and ascocarps. In 2010, a single hazel tree selected for its high truffle (Tuber melanosporum) production and situated in the west part of the Vosges, France, was labeled with ¹³CO₂. The transfer of ¹³C from the leaves to the fine roots and T. melanosporum mycorrhizas was very slow compared with the results found in the literature for herbaceous plants or other tree species. The fine roots primarily acted as a carbon conduit; they accumulated little ¹³C and transferred it slowly to the mycorrhizas. The mycorrhizas first formed a carbon sink and accumulated ¹³C prior to ascocarp development. Then, the mycorrhizas transferred ¹³C to the ascocarps to provide constitutive carbon (1.7 mg of ¹³C per day). The ascocarps accumulated host carbon until reaching complete maturity, 200 days after the first labeling and 150 days after the second labeling event. This role of the Tuber ascocarps as a carbon sink occurred several months after the end of carbon assimilation by the host and at low temperature. This finding suggests that carbon allocated to the ascocarps during winter was provided by reserve compounds stored in the wood and hydrolyzed during a period of frost. Almost all of the constitutive carbon allocated to the truffles (1% of the total carbon assimilated by the tree during the growing season) came from the host.

Mechanisms of nitrosylation and denitrosylation of cytoplasmic glyceraldehyde-3-phosphate dehydrogenase from Arabidopsis thaliana
M Zaffagnini, S Morisse, M Bedhomme, CH Marchand, M Festa, N Rouhier, SD …
Journal of Biological Chemistry

Abstract

Nitrosylation is a reversible post-translational modification of protein cysteines playing a major role in cellular regulation and signaling in many organisms including plants where it has been implicated in the regulation of immunity and cell death. The extent of nitrosylation of a given cysteine residue is governed by the equilibrium between nitrosylation and denitrosylation reactions. The mechanisms of these reactions remain poorly studied in plants. In the present work, we have employed glycolytic GAPDH from Arabidopsis thaliana as a tool to investigate the molecular mechanisms of nitrosylation and denitrosylation using a combination of approaches including activity assays, the biotin switch technique, site-directed mutagenesis and mass spectrometry. Arabidopsis GAPDH activity was reversibly inhibited by nitrosylation of catalytic Cys-149 mediated either chemically with a strong NO donor or by transnitrosylation with GSNO. GSNO was found to trigger both GAPDH nitrosylation and glutathionylation although nitrosylation was widely prominent. Arabidopsis GAPDH was found to be denitrosylated by GSH but not by plant cytoplasmic thioredoxins. GSH fully converted nitrosylated GAPDH to the reduced, active enzyme, without forming any glutathionylated GAPDH. Thus, we found that nitrosylation of GAPDH is not a step towards formation of the more stable glutathionylated enzyme. GSH-dependent denitrosylation of GapC1 was found to be linked to the [GSH]/[GSNO] ratio and to be independent of the [GSH]/[GSSG] ratio. The possible importance of these biochemical properties for the regulation of Arabidopsis GAPDH functions in vivo is discussed.

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