Molecular Mycorrhizal symbiosis

Martin, Francis, ed. Molecular Mycorrhizal Symbiosis. John Wiley & Sons, 2016.

Dissecting the metabolic role of mitochondria during developmental leaf senescence D Chrobok, SR Law, B Brouwer, P Lindén, A Ziolkowska, D Liebsch, … Plant Physiology, pp. 01463.2016

Abstract

The functions of mitochondria during leaf senescence, a type of programmed cell death aiming at the massive retrieval of nutrients from the senescing organ to the rest of the plant, remain elusive. Here, combining experimental and analytical approaches, we showed that mitochondrial integrity is conserved until the latest stages of leaf senescence, while their number drops by 30%. Adenylate phosphorylation state assays and mitochondrial respiratory measurements indicated that the leaf energy status is also maintained during this time period. Further, after establishing a curated list of genes coding for products targeted to mitochondria, we analysed in isolation their transcript profiles, focusing on several key mitochondrial functions such as the tricarboxylic acid cycle, mitochondrial electron transfer chain, iron-sulphur cluster biosynthesis, transporters as well as catabolic pathways. In tandem with a metabolomic approach, our data indicated that mitochondrial metabolism was reorganised to support the selective catabolism of both amino- and fatty acids. Such adjustments would ensure the replenishment of α-ketoglutarate and glutamate, which provide the carbon backbones for nitrogen remobilisation. Glutamate, being the substrate of the strongly up-regulated cytosolic glutamine synthase, is likely to become a metabolically limiting factor in the latest stages of developmental leaf senescence. Finally, an evolutionary age analysis revealed that while branched-chain amino acid and proline catabolism are very old mitochondrial functions particularly enriched at the latest stages of leaf senescence, auxin metabolism appeared rather newly acquired. In summation, our work shows that during developmental leaf senescence, mitochondria orchestrate catabolic processes by becoming increasingly central energy and metabolic hubs.

Trapping truffle production in holes: a promising technique for improving production and unravelling truffle life cycle C Murat, L Bonneau, H De La Varga, JM Olivier, S Fizzala,.. Italian Journal of Mycology 45, 47-53

Abstract

The Périgord black truffle, Tuber melanosporum Vittad., is an ectomycorrhizal fungus that forms edible hypogeous ascomata. It is now harvested in plantations and is recognized as an agricultural product by European policy. Empirical techniques without scientific demonstration of their efficiency are often used to improve the production of truffles in plantations. One of these techniques is “truffle trapping” which consists in practicing holes inside the potential productive area and to fill them with a substrate containing ascospores. We report an experiment in a truffle orchard where 784 holes were set under 196 trees. Two years after the installation of the holes, 95% of the truffles were found inside the holes corresponding to only 5% of the productive area. This study confirms the efficiency of this empirical technique and demonstrates new ways for in situ studies of the truffle life cycle.

Ecology of the forest microbiome: Highlights of temperate and boreal ecosystems S Uroz, M Buée, A Deveau, S Mieszkin, F Martin. Soil Biology and Biochemistry 103, 471-488

Abstract

Due to land use history, most of the current temperate and boreal forests are developed on nutrient-poor and rocky soils, keeping fertile soils for agriculture. Consequently, the conditions occurring in forest ecosystems strongly differ from those of other terrestrial environments, giving importance to the access of nutritive elements and their recycling for the long-lasting development of forest ecosystems. In this review, we present an overview of the recent findings on the relationships between bacterial and fungal communities and their tree hosts at both the taxonomic and functional levels. We highlighted the common and different deterministic drivers of these microbial communities, focusing on the tree species effect, the different interfaces existing between the trees and their environment, the impact of tree by-products (decaying wood and litter), the impact of soil and seasonal changes, and lastly, the consequences of forestry practices. Depicting both taxonomic and functional diversity based on cultivation-dependent and -independent analyses, we highlight the distribution patterns and the functional traits characterizing bacterial and fungal communities. We also discuss the importance of bridging environmental microbiology to genomics and how to integrate the interactions between microorganisms for a better understanding of tree growth and health.

Crystal Structure of Saccharomyces cerevisiae ECM4, a Xi-Class Glutathione Transferase that Reacts with Glutathionyl-(hydro) quinones M Schwartz, C Didierjean, A Hecker, JM Girardet, M Morel-Rouhier, … PLOS ONE 11 (10), e0164678

Abstract

Glutathionyl-hydroquinone reductases (GHRs) belong to the recently characterized Xi-class of glutathione transferases (GSTXs) according to unique structural properties and are present in all but animal kingdoms. The GHR ScECM4 from the yeast Saccharomyces cerevisiae has been studied since 1997 when it was found to be potentially involved in cell-wall biosynthesis. Up to now and in spite of biological studies made on this enzyme, its physiological role remains challenging. The work here reports its crystallographic study. In addition to exhibiting the general GSTX structural features, ScECM4 shows extensions including a huge loop which contributes to the quaternary assembly. These structural extensions are probably specific to Saccharomycetaceae. Soaking of ScECM4 crystals with GS-menadione results in a structure where glutathione forms a mixed disulfide bond with the cysteine 46. Solution studies confirm that ScECM4 has reductase activity for GS-menadione in presence of glutathione. Moreover, the high resolution structures allowed us to propose new roles of conserved residues of the active site to assist the cysteine 46 during the catalytic act.

Genetic diversity and origins of the homoploid allopolyploid hybrid Phytophthora× alni. J Aguayo, F Halkett, C Husson, ZÁ Nagy, A Szigethy, J Bakonyi, P Frey, … Applied and Environmental Microbiology, AEM. 02221-16

Abstract

Soil type determines the distribution of nutrient mobilizing bacterial communities in the rhizosphere of beech trees O Nicolitch, Y Colin, MP Turpault, S Uroz. Soil Biology and Biochemistry 103, 429-445

Abstract

Rhizosphere represents a nutrient-rich environment and a hotspot of bacterial activities compared to the surrounding bulk soil. However, few studies have investigated how this rhizosphere effect depends on the soil conditions, and never for trees. Contrary to annual plants, trees need decades to grow and strongly depend on the access and recycling of soil nutrients and water. In this context, we aimed at understanding if contrasted soil types impact the taxonomy and functions of bacterial communities inhabiting beech rhizosphere. To test this hypothesis, we considered the natural toposequence of Montiers, which is characterized by a same land cover dominated by beech (Fagus sylvatica) trees of the same age, growing under the same climatic conditions and under the same forestry practices. We used a combination of in vitro bioassays and 16S rRNA gene sequences analyses on a collection of 370 bacterial strains generated from beech rhizosphere and surrounding bulk soil samples collected in the organo-mineral horizon along the toposequence. Our study highlighted an increasing beech rhizosphere effect from the nutrient-rich to nutrient-poor soils, with specific bacterial functions related to inorganic nutrient mobilization largely and exclusively enriched in the rhizosphere of the nutrient-poor soils. This functional selection in the rhizosphere came with an enrichment of bacterial strains assigned to the Burkholderia and Collimonas genus, which appeared to be the dominant and most effective mineral-weathering bacteria. Our data corroborate the hypothesis of a variable selection of specific rhizosphere bacterial communities by beech trees according to the soil conditions and the tree nutritional requirements.