Article: Environmental microbiology

First evidences that the ectomycorrhizal fungus Paxillus involutus mobilizes nitrogen and carbon from saprotrophic fungus necromass E Akroume, F Maillard, C Bach, C Hossann, C Brechet, N Angeli, B Zeller, … Environmental microbiology

Summary

Fungal succession in rotting wood shows a surprising abundance of ectomycorrhizal (EM) fungi during the late decomposition stages. To better understand the links between EM fungi and saprotrophic fungi, we investigated the potential capacities of the EM fungus Paxillus involutus to mobilize nutrients from necromass of Postia placenta, a wood rot fungus, and to transfer these elements to its host tree. In this aim, we used pure cultures of P. involutus in the presence of labelled Postia necromass (15N/13C) as nutrient source, and a monoxenic mycorrhized pine experiment also, composed of labelled Postianecromass and P. involutus culture in interaction with pine seedlings. The isotopic labelling was measured in both experiments. In pure culture, P. involutus was able to mobilize N, but C as well, from the Postia necromass. In the symbiotic interaction experiment, we measured high 15N enrichments in all plant and fungal compartments. Interestingly, 13C remains mainly in the mycelium and mycorrhizas, demonstrating that the EM fungus transferred essentially N from the necromass to the tree. These observations reveal that fungal organic matter could represent a significant N source for EM fungi and trees, but also a C source for mycorrhizal fungi, including in symbiotic lifestyle.

Article: Scientific reports

A rust fungal effector binds plant DNA and modulates transcription MB Ahmed, KCG dos Santos, IB Sanchez, B Petre, C Lorrain, MB Plourde, … Scientific Reports 8 (1), 14718

Abstract

The basidiomycete Melampsora larici-populina causes poplar rust disease by invading leaf tissues and secreting effector proteins through specialized infection structures known as haustoria. The mechanisms by which rust effectors promote pathogen virulence are poorly understood. The present study characterized Mlp124478, a candidate effector of M. larici-populina. We used the models Arabidopsis thalianaand Nicotiana benthamiana to investigate the function of Mlp124478 in plant cells. We established that Mlp124478 accumulates in the nucleus and nucleolus, however its nucleolar accumulation is not required to promote growth of the oomycete pathogen Hyaloperonospora arabidopsidis. Stable constitutive expression of Mlp124478 in A. thalianarepressed the expression of genes involved in immune responses, and also altered leaf morphology by increasing the waviness of rosette leaves. Chip-PCR experiments showed that Mlp124478 associats’e with the TGA1a-binding DNA sequence. Our results suggest that Mlp124478 exerts a virulence activity and binds the TGA1a promoter to suppress genes induced in response to pathogen infection.

Article: New Phytologist

Oxidative protein folding: state‐of‐the‐art and current avenues of research in plants. AJ Meyer, J Riemer, N Rouhier. New Phytologist

Summary

Disulfide bonds are post‐translational modifications crucial for the structure and function of thousands of proteins. Their formation and isomerization, referred to as oxidative folding, require specific protein machineries found in oxidizing subcellular compartments, namely the endoplasmic reticulum and the associated endomembrane system, the intermembrane space of mitochondria and the thylakoid lumen of chloroplasts. At least one protein component is required for transferring electrons from substrate proteins to an acceptor that is usually molecular oxygen. For oxidation reactions, incoming reduced substrates are oxidized by thiol‐oxidoreductase proteins (or domains in case of chimeric proteins), which are usually themselves oxidized by a single thiol oxidase, the enzyme generating disulfide bonds de novo. By contrast, the description of the molecular actors and pathways involved in proofreading and isomerization of misfolded proteins, which require a tightly controlled redox balance, lags behind. Herein we provide a general overview of the knowledge acquired on the systems responsible for oxidative protein folding in photosynthetic organisms, highlighting their particularities compared to other eukaryotes. Current research challenges are discussed including the importance and specificity of these oxidation systems in the context of the existence of reducing systems in the same compartments.

Article: Environmental Microbiology

Oak extractive‐induced stress reveals the involvement of new enzymes in the early detoxification response of Phanerochaete chrysosporium AJ Fernández‐González, N Valette, A Kohler, S Dumarçay, R Sormani, … Environmental microbiology

Summary

Extensive evidence showed that the efficiency of fungal wood degradation is closely dependent on their ability to cope with the myriad of putative toxic compounds called extractives released during this process. By analyzing global gene expression of Phanerochaete chrysosporium after short oak extractive treatment (1, 3 and 6h), we show that the early molecular response of the fungus concerns first mitochondrial stress rescue followed by the oxidation and finally conjugation of the compounds. During these early responses, the lignolytic degradative system is not induced, rather some small secreted proteins (SSP) could play an important role in cell protection or signaling. By focusing on the functional characterization of an hitherto uncharacterized glutathione transferase, we show that this enzyme interacts with wood molecules suggesting that it could be involved in the detoxification of some of them, or act as a scavenger to prevent their cytosolic toxicity and favor their transport.

Article : Fungal Ecology

From leaf to continent: The multi-scale distribution of an invasive cryptic pathogen complex on oak ML Desprez-Loustau, M Massot, M Toïgo, T Fort, AGA Kaya, J Boberg, …Fungal Ecology 36, 39-50

Abstract

The spatial distribution and niche differentiation of three closely related species (Erysiphealphitoides, Erysiphe quercicola and Erysiphe hypophylla) causing oak powdery mildew was studied at scales ranging from the European continent, where they are invasive, to a single leaf. While E. alphitoides was dominant at all scales, E. quercicola and E. hypophylla had restricted geographic, stand and leaf distributions. The large-scale distributions were likely explained by climatic factors and species environmental tolerances, with E. quercicola being more frequent in warmer climates and E. hypophylla in colder climates. The extensive sampling and molecular analyses revealed the cryptic invasion of E. quercicola in nine countries from which it had not previously been recorded. The presence of the three species was also strongly affected by host factors, such as oak species and developmental stage. Segregation patterns between Erysiphe species were observed at the leaf scale, between and within leaf surfaces, suggesting competitive effects.

Article: Proceedings of the IUFRO conference

Genomics, transcriptomics, and effectoromics of the poplar leaf rust fungus Melampsora larici-populina B Petre, S Hacquard, A Persoons, N Saveleva, E Tisserant, E Morin, …In: Schoettle, Anna W.; Sniezko, Richard A.; Kliejunas, John T., eds …

Description

Melampsora larici-populina is causing leaf rust disease in poplar (Populus spp.) worldwide and poses serious problems to poplar breeders in France and in northern Europe. As with other rust fungi, its obligate biotroph status hinders laboratory investigations. Understanding the biology of rust fungi and deciphering the molecular mechanisms underlying biotrophy have long been a problem. Most of the knowledge gained was largely descriptive and limited to a few rust species; only recently has substantial progress been made in the characterization of avirulence determinants of the flax rust Melampsora lini.

Article: Proceedings of the National Academy of Sciences

Dark deactivation of chloroplast enzymes finally comes to light. JP Jacquot. P. Proceedings of the National Academy of Sciences

From the pioneering work that the Buchanan group started in the late 1960s, we know that the division of photosynthesis into light and dark reactions is inade- quate because the activity of a number of chloroplast enzymes, many involved in the Calvin–Benson cycle, is strictly controlled by light; that is, they are activated in the light and deactivated in the dark. An exception is glucose-6-phosphate dehydrogenase, which is regulated in an opposite manner; that is, activation in the dark and deactivation in the light. It took a decade to biochemically dissect the newly identifed redox regula- tory pathway responsible for this regulation. Known as the ferredoxin-thioredoxin system, the pathway is com- posed of three components: ferredoxin, ferredoxin- thioredoxin reductase (FTR), and thioredoxin (Trx) that relay the reducing power generated at photosystem 1 (PS1) to target regulatory enzymes (1, 2).

Article : ACS Sustainable Chemistry & Engineering

Fungal glutathione transferases as tools to explore the chemical diversity of Amazonian wood extractives T Perrot, mathieu Schwartz, F Saiag, G Salzet, S Dumarcay, F Favier, … ACS Sustainable Chemistry & Engineering

Abstract

The natural durability of wood is linked to its chemical composition and in particular the presence of metabolites called extractives that possess often chemical reactivity. To deal with these compounds, wood degraders have developed detoxification systems usually involving enzyme families. Among these enzymes, glutathione transferases (GSTs) are involved in the decrease of the reactivity of toxic compounds. In this study, the hypothesis that the detoxification systems of wood decaying fungi could be indicators of the chemical reactivity of wood extracts has been tested. This approach has been evaluated using thirty-two wood extracts coming from French Guiana species, testing their antimicrobial ability, their antioxidative properties and their reactivity against six GSTs from the white rot Trametes versicolor. From the obtained data, a significant correlation between the antimicrobial and antioxidative properties of the tested wood extracts and GSTs interaction was established. In addition, the chemical analysis performed on one of the most reactive extract (an acetonic extract of Bagassa guianensis) has demonstrated oxyresveratrol as a major constituent. We were able to co-crystallize one GST with this commercially interesting compound. Taken together, the presented data support the hypothesis that detoxifying enzymes could be used to identify presence of molecules of industrial interest in wood extracts.

Article: European Journal of Plant Pathology

Impact of soil chemistry, nutrient supplements, and fungicides on the health and yield of field-grown processing tomatoes NN Maharaj, EM Miyao, RM Davis, S Uroz, JHJ Leveau. European Journal of Plant Pathology, 1-1

Abstract

We report the results of a 3-year study in which we collected and analyzed soil and yield data from experimental plots in six commercial processing tomato fields in Yolo and Solano counties in California. Our objective was to assess the effect of soil chemistry and soil-delivered nutrients and fungicides on tomato plant health and fruit yield at harvest. Marketable yield, leaf necrosis, and fruit loss due to sunburn differed significantly between individual fields, with averages ranging from 81.2–138.5 Mg ha−1, 32–72% leaf necrosis and 1.9 to 8.8% sunburnt fruit, respectively. Higher-yielding fields showed significantly lower levels of leaf necrosis and sunburn damage and a positive correlation with pre-plant soil parameters such as potassium concentration and cation exchange capacity (CEC). Interestingly, soil amendments of composted poultry manure or other nutrient supplements in low-CEC fields, but not high-CEC fields, resulted in higher fruit yield and less leaf necrosis. While all fields showed symptoms typical of Verticillium wilt and some fields showed symptoms of Fusarium wilt, Fusarium crown and root rot, corky root, and root knot nematode, none of our soil amendments, including chemical and biological fungicides, significantly or consistently reduced incidence or severity of these diseases. We discuss our findings in the context of premature vine decline of tomato, an emerging phenomenon in production fields in the Sacramento Valley, which is characterized by the loss of plant vigor and canopy cover at the onset of fruit ripening and for which causative agent(s) and management options in California remain elusive.