Fine-scale genetic structure of natural Tuber aestivum sites in southern Germany V Molinier, C Murat, A Baltensweiler, U Büntgen, F Martin, B Meier, … Mycorrhiza, 1-13

Abstract

Although the Burgundy truffle (Tuber aestivum) is an ectomycorrhizal fungus of important economic value, its subterranean life cycle and population biology are still poorly understood. Here, we determine mating type and simple sequence repeat (SSR) maternal genotypes of mapped fruiting bodies to assess their genetic structure within two naturally colonized forest sites in southern Germany. Forty-one genotypes were identified from 112 fruiting bodies. According to their mating types, the maternal genotypes were aggregated only in one population. Genotypic diversity of individuals that mostly were small and occurred in 1 out of 2 years of sampling was high. Although these results suggested a ruderal colonization strategy, some genets spread several hundred meters. This result indicates that, besides sexual spore dispersal, vegetative growth or spreading by mycelial propagules contributes to dissemination. In one site, fewer individuals with a tendency to expand genets belonging to only one genetic group were observed. In the second site, numerous small individuals were found and were grouped into two clearly differentiated genetic groups that were spatially intermingled. Forest characteristics and disturbances are possible reasons for the observed genetic patterns. Our findings contribute to a better understanding of the biology of one of the most widespread and commercially important truffle species. This knowledge is critical for establishing and maintaining sustainable long-term truffle cultivations.

Plastidic P2 glucose-6P dehydrogenase from poplar is modulated by thioredoxin m-type: distinct roles of cysteine residues in redox regulation and NADPH inhibition M Cardi, M Zaffagnini, A De Lillo, D Castiglia, K Chibani, JM Gualberto, …Plant Science

Abstract

A cDNA coding for a plastidic P2-type G6PDH isoform from poplar (Populus tremula x tremuloides) has been used to express and purify to homogeneity the mature recombinant protein with a N-terminus His-tag. The study of the kinetic properties of the recombinant enzyme showed an in vitro redox sensing modulation exerted by reduced DTT. The interaction with thioredoxins (TRXs) was then investigated.

Five cysteine to serine variants (C145S – C175S – C183S – C195S – C242S) and a variant with a double substitution for Cys¹⁷⁵ and Cys¹⁸³ (C175S/C183S) have been generated, purified and biochemically characterized in order to investigate the specific role(s) of cysteines in terms of redox regulation and NADPH-dependent inhibition.

Three cysteine residues (C¹⁴⁵, C¹⁹⁴, C²⁴²) are suggested to have a role in controlling the NADP⁺ access to the active site, and in stabilizing the NADPH regulatory binding site.

Our results also indicate that the regulatory disulfide involves residues Cys¹⁷⁵ and Cys¹⁸³ in a position similar to those of chloroplastic P1-G6PDHs, but the modulation is exerted primarily by TRX m-type, in contrast to P1-G6PDH, which is regulated by TRX f.

This unexpected specificity indicates differences in the mechanism of regulation, and redox sensing of plastidic P2-G6PDH compared to chloroplastic P1-G6PDH in higher plants.

Into the functional ecology of ectomycorrhizal communities: environmental filtering of enzymatic activities. PE Courty, F Munoz, MA Selosse, M Duchemin, S Criquet, F Ziarelli, … Journal of Ecology

Abstract

1.Characterizing the ecological processes driving the assembly and functional composition of ectomycorrhizal (ECM) fungal communities is an area of active research.

2.Here, we applied a trait-based framework to address whether and how environmental filtering and niche differentiation influence the diversity of ECM fungal enzymatic activities in two oak-dominated forest ecosystems. We hypothesized that fungal enzymatic activities and ECM community assembly are influenced by the availability of targeted resources in the surrounding soil.

3.We pinpointed a major influence of environmental filtering on ECM fungal taxonomic and functional composition. Contrasted taxonomic composition among forest ecosystems was linked to broad interspecific trait variation and entailed contrasted functional responses at community-level. However, intraspecific trait variation contributed to community response within ecosystems. We characterized a strong relationship between enzymatic activities and targeted resource availability in surrounding soil, suggesting a functional role of the enzymes for the acquisition of these resources. Conversely, we did not find a significant influence of niche differentiation in ECM community assembly.

4.Synthesis. Heterogeneous distribution of soil resources drives a community-level functional response and determines the functional and taxonomic mosaic of ECM communities in forest ecosystems.

Tree species select diverse soil fungal communities expressing different sets of lignocellulolytic enzyme-encoding genes

F Barbi, E Prudent, L Vallon, M Buée, A Dubost… – Soil Biology and …, 2016

Specific impacts of beech and Norway spruce on the structure and diversity of the rhizosphere and soil microbial communities S Uroz, P Oger, E Tisserand, A Cébron, MP Turpault, M Buée, W De Boer, … Scientific Reports 6, 27756

Abstract

The impacts of plant species on the microbial communities and physico-chemical characteristics of soil are well documented for many herbs, grasses and legumes but much less so for tree species. Here, we investigate by rRNA and ITS amplicon sequencing the diversity of microorganisms from the three domains of life (Archaea, Bacteria and Eukaryota:Fungi) in soil samples taken from the forest experimental site of Breuil-Chenue (France). We discovered significant differences in the abundance, composition and structure of the microbial communities associated with two phylogenetically distant tree species of the same age, deciduous European beech (Fagus sylvatica) and coniferous Norway spruce (Picea abies Karst), planted in the same soil. Our results suggest a significant effect of tree species on soil microbiota though in different ways for each of the three microbial groups. Fungal and archaeal community structures and compositions are mainly determined according to tree species, whereas bacterial communities differ to a great degree between rhizosphere and bulk soils, regardless of the tree species. These results were confirmed by quantitative PCR, which revealed significant enrichment of specific bacterial genera, such as Burkholderia and Collimonas, known for their ability to weather minerals within the tree root vicinity.

Chloroplast FBPase and SBPase are thioredoxin-linked enzymes with similar architecture but different evolutionary histories DD Gütle, T Roret, SJ Müller, J Couturier, SD Lemaire, A Hecker, …Proceedings of the National Academy of Sciences, 201606241

Abstract

The Calvin–Benson cycle of carbon dioxide fixation in chloroplasts is controlled by light-dependent redox reactions that target specific enzymes. Of the regulatory members of the cycle, our knowledge of sedoheptulose-1,7-bisphosphatase (SBPase) is particularly scanty, despite growing evidence for its importance and link to plant productivity. To help fill this gap, we have purified, crystallized, and characterized the recombinant form of the enzyme together with the better studied fructose-1,6-bisphosphatase (FBPase), in both cases from the moss Physcomitrella patens (Pp). Overall, the moss enzymes resembled their counterparts from seed plants, including oligomeric organization—PpSBPase is a dimer, and PpFBPase is a tetramer. The two phosphatases showed striking structural homology to each other, differing primarily in their solvent-exposed surface areas in a manner accounting for their specificity for seven-carbon (sedoheptulose) and six-carbon (fructose) sugar bisphosphate substrates. The two enzymes had a similar redox potential for their regulatory redox-active disulfides (−310 mV for PpSBPase vs. −290 mV for PpFBPase), requirement for Mg2+ and thioredoxin (TRX) specificity (TRX f > TRX m). Previously known to differ in the position and sequence of their regulatory cysteines, the enzymes unexpectedly showed unique evolutionary histories. The FBPase gene originated in bacteria in conjunction with the endosymbiotic event giving rise to mitochondria, whereas SBPase arose from an archaeal gene resident in the eukaryotic host. These findings raise the question of how enzymes with such different evolutionary origins achieved structural similarity and adapted to control by the same light-dependent photosynthetic mechanism—namely ferredoxin, ferredoxin-thioredoxin reductase, and thioredoxin.

Role of secondary metabolites in the interaction between Pseudomonas fluorescens and soil microorganisms under iron limited conditions A Deveau, H Gross, B Palin, S Mehnaz, M Schnepf, P Leblond, … FEMS Microbiology Ecology, fiw107

Mineral Type and Solution Chemistry Affect the Structure and Composition of Actively Growing Bacterial Communities as Revealed by Bromodeoxyuridine Immunocapture and 16S rRNA Pyrosequencing. LC Kelly, Y Colin, MP Turpault, S Uroz. Microbial ecology, 1-15

Abstract

Understanding how minerals affect bacterial communities and their in situ activities in relation to environmental conditions are central issues in soil microbial ecology, as minerals represent essential reservoirs of inorganic nutrients for the biosphere. To determine the impact of mineral type and solution chemistry on soil bacterial communities, we compared the diversity, composition, and functional abilities of a soil bacterial community incubated in presence/absence of different mineral types (apatite, biotite, obsidian). Microcosms were prepared containing different liquid culture media devoid of particular essential nutrients, the nutrients provided only in the introduced minerals and therefore only available to the microbial community through mineral dissolution by biotic and/or abiotic processes. By combining functional screening of bacterial isolates and community analysis by bromodeoxyuridine DNA immunocapture and 16S rRNA gene pyrosequencing, we demonstrated that bacterial communities were mainly impacted by the solution chemistry at the taxonomic level and by the mineral type at the functional level. Metabolically active bacterial communities varied with solution chemistry and mineral type. Burkholderia were significantly enriched in the obsidian treatment compared to the biotite treatment and were the most effective isolates at solubilizing phosphorous or mobilizing iron, in all the treatments. A detailed analysis revealed that the 16S rRNA gene sequences of the OTUs or isolated strains assigned as Burkholderia in our study showed high homology with effective mineral-weathering bacteria previously recovered from the same experimental site.

Secretion of small proteins is species‐specific within Aspergillus sp. N Valette, I Benoit‐Gelber, MD Falco, A Wiebenga, RP Vries, E Gelhaye, … Microbial Biotechnology

Summary

Small secreted proteins (SSP) have been defined as proteins containing a signal peptide and a sequence of less than 300 amino acids. In this analysis, we have compared the secretion pattern of SSPs among eight aspergilli species in the context of plant biomass degradation and have highlighted putative interesting candidates that could be involved in the degradative process or in the strategies developed by fungi to resist the associated stress that could be due to the toxicity of some aromatic compounds or reactive oxygen species released during degradation. Among these candidates, for example, some stress-related superoxide dismutases or some hydrophobic surface binding proteins (HsbA) are specifically secreted according to the species . Since these latter proteins are able to recruit lytic enzymes to the surface of hydrophobic solid materials and promote their degradation, a synergistic action of HsbA with the degradative system may be considered and need further investigations. These SSPs could have great applications in biotechnology by optimizing the efficiency of the enzymatic systems for biomass degradation.

Influence of site and stand factors on Hymenoscyphus fraxineus induced basal lesion. B Marçais, C Husson, L Godart, O Caël. Plant Pathology

 Summary