Interactions Arbres-Microorganismes

ABSTRACT Increasingly frequent drought events can favour forest disease emergence. Sooty bark disease (SBD) of Acer pseudoplatanus (sycamore maple) is a good example of this phenomenon. Records of its causal agent, Cryptostroma corticale , invasive in Europe, have increased since the 2000s in central and southern Europe. The pathogen is found asymptomatically in host tissues and switches to a pathogenic lifestyle following abiotic stress. This latent phase hinders the pathogen's early detection. In this study, we assessed the prevalence of C. corticale in asymptomatic trees in France. Our study covered six regions, each including a city and its nearby peri‐urban and forested ecosystems, representing a human gradient of influence. We assessed the pathogen's presence in 540 wood samples from asymptomatic maple trees by using real‐time PCR. The prevalence was 13.6%, across all plots. The pathogen appears to be widespread in the natural sycamore maple stands of France, increasing the risk of disease development following future drought events. Host density and 3‐year accumulated water deficit best explained detection of C. corticale in asymptomatic sycamore maples. However, the detection of the fungus was not related to the level of human influence, as no significant differences were observed along the urban‐to‐forest gradient. Furthermore, C. corticale was detected in asymptomatic hosts even in regions with limited reports of SBD, indicating that the local reporting frequency of the disease does not reflect the latent presence of the pathogen.

During wood degradation, fungi have to deal with toxic and stressful compounds called wood extractives. The identification of the various detoxification strategies developed by fungi, and the molecular targets of these compounds is limited in Basidiomycetes because of the lack of genetic tools. To circumvent this problem, we have developed a direct genetic strategy in the white-rot fungus Phanerochaete chrysosporium. A library of P. chrysosporium UV mutants was generated and screened to isolate mutants resistant to Bagassa guianensis wood extractives (BWE). Wood extractives contribute to B. guianensis wood durability, and resistance to those extractives confers to the mutants a better ability to mineralise wood sawdust. This resistance phenotype is due to causal mutation(s) in the gene coding for an ortholog of the human DENND6, a protein involved in endocytic recycling. Using in silico and invivo assays, we identified that moracin N, found in BWE, has antifungal activity likely by binding onto the wild type PcDENND6 protein but not onto the mutated variant.

Abstract Heartwood formation is a complex process that contributes to ensuring the integrity of trunks and the longevity of trees. We examined this mechanism in the tropical angiosperm Sextonia rubra (Mez.) van der Werff in relation to the spatial distribution of specialized metabolites and their functional role at the scale of a mature individual. Heartwood formation was analyzed starting from the examination of one of its properties, namely the decay resistance, of the different S. rubra wood tissues (sapwood, heartwood and pith) using soil bed tests. Annotation and identification of the metabolites present in ethyl acetate extracts were carried out by reverse-phase liquid chromatography coupled to a tandem mass spectrometer (RPLC-ESI-MS/MS) and molecular networks. Following the application of supervised statistical analyses and the use of glutathione S-transferases enzymatic assays, the specialized metabolites of interest were quantified radially and longitudinally in the different tissues using a RPLC-ESI-HRMS system. Heartwood and pith were shown to resist degradation after a 10-month exposure to forest soil, with no effect of the heartwood cambial age. Molecular diversity was specific to each tissue type, with flavonoids and butanolides detected in bark and sapwood, while alkaloids and butyrolactones were identified in heartwood and pith. Supervised analyses and enzyme assays suggested that alkaloids and butyrolactones play a role in the resistance of internal tissues to degradation. Butyrolactone concentrations peaked in the middle heartwood but remained homogeneous longitudinally, while alkaloid concentrations were uniform longitudinally and radially in the heartwood. In conclusion, the resistance of heartwood and pith to fungal degradation was correlated with the accumulation of lactones and alkaloids. While butanolide precursors of butyrolactones have been detected in the sapwood, alkaloids appear to be directly biosynthesized in the heartwood. This suggests that the biosynthesis and accumulation of specialized metabolites during heartwood formation is specific to each molecular family.

Hydrolysates can be obtained by enzymatic treatments and present various bioactivities and functional properties such as antioxidant, metal-chelation etc ., enabling their industrial application. These activities depend on amino acid composition, peptides size profile, peptide structure, which are related to proteolysis conditions. Hence, pea protein hydrolysates were produced by either Alcalase® followed by Flavourzyme® (Alc + Flav≤1 kDa) or Protamex® followed by Flavourzyme® (Prot + Flav≤1 kDa). Physico-chemical characterization of these hydrolysates shows that Prot + Flav≤1 kDa hydrolysate has higher degree of hydrolysis and and thus, higher small-size peptides quantity compared to Alc + Flav≤1 kDa. Besides, switchSENSE® technology allowed to unveil the presence of Ni 2+ chelating peptides, demonstrating the high potential of such innovative technology to screen metal-complexing peptides in hydrolysates. Moreover, the Prot + Flav≤1 kDa hydrolysate shows higher radical scavenging and reducing power, related to its higher degree of hydrolysis and small-size peptides quantity. The peptides identified in both hydrolysates by LC-MS/MS analysis contain high amount of aspartic acid, glutamic acid, proline, leucine, valine and glycine, which might be responsible of their antioxidant properties. The sequential proteolysis may increase metal chelating and antioxidant activities of hydrolysates. • SwitchSENSE evidences the presence of Ni 2+ chelating peptides in pea hydrolysates. •Pea hydrolysate can be valorized as antioxidants. •Metal chelating peptides with antioxidants activities were identified by LC/MS/MS. •Hydrolysates physicochemical properties were correlated to their antioxidant ones.

Hymenoscyphus fraxineus is an invasive forest fungal pathogen that induces severe dieback in European ash populations. The spread of the disease has been closely monitored in France by the forest health survey system. We have developed a mechanisticstatistical model that describes the spread of the disease. It takes into account climate (summer temperature and spring rainfall), pathogen population dynamics (foliar infection, Allee effect induced by limited sexual partner encounters) and host density. We fitted this model using available disease reports. We estimated the parameters of our model, first identifying the appropriate ranges for the parameters, which led to a model reduction, and then using an adaptive multiple importance sampling algorithm for fitting. The model reproduces well the propagation observed in France over the last 20 years. In particular, it predicts the absence of disease impact in the south-east of the country and its weak development in the Garonne valley in south-west France. Summer temperature is the factor with the highest overall effect on disease spread, and explains the limited impact in southern France. Among the different temperature indices tested, the number of summer days with temperatures above 28{\textdegree}C gave the best qualitative behavior and the best fit. In contrast, the Allee effect and the heterogeneity of spring precipitation did not strongly affect the overall expansion of H. fraxineus in France and could be neglected in the modeling process. The model can be used to infer the average annual dispersal of H. fraxineus in France.

About 50 proteins expressed in plastids of photosynthetic eukaryotes ligate iron‑sulfur (Fe-S) clusters and ensure vital functions in photosynthesis, sulfur and nitrogen assimilation, but also in the synthesis of pigments, vitamins and hormones. The synthesis of these Fe-S clusters, which are co- or post-translationally incorporated into these proteins, relies on several proteins belonging to the so-called sulfur mobilization (SUF) machinery. An Fe-S cluster is first de novo synthesized on a scaffold protein complex before additional late-acting maturation factors act in the specific transfer, possible conversion and insertion of this cluster into target recipient proteins. In this review, we will summarize what is known about the molecular mechanisms responsible for both the synthesis and transfer steps, focusing in particular on the structural aspects that allow the formation of the required protein complexes.

ABSTRACTThe linear chromosome ofStreptomycesexhibits a highly compartmentalized structure with a conserved central region flanked by variable arms. As double strand break (DSB) repair mechanisms play a crucial role in shaping the genome plasticity ofStreptomyces, we investigated the role of EndoMS/NucS, a recently characterized endonuclease involved in a non-canonical Mismatch Repair (MMR) mechanism in archaea and actinobacteria, that singularly corrects mismatches by creating a DSB. We showed thatStreptomycesmutants lacking NucS display a marked colonial phenotype and a drastic increase in spontaneous mutation rate.In vitrobiochemical assays revealed that NucS cooperates with the replication clamp to efficiently cleave G/T, G/G and T/T mismatched DNA by producing DSBs. These findings are consistent with the transition-shifted mutational spectrum observed in the mutant strains and reveal that NucS-dependent MMR specific task is to eliminate G/T mismatches generated by the DNA polymerase during replication. Interestingly, our data unveil a crescent-shaped distribution of the transition frequency from the replication origin towards the chromosomal ends, shedding light on a possible link between NucS-mediated DSBs andStreptomycesgenome evolution.GRAPHICAL ABSTRACT

IntroductionThe depolymerization of lignocellulose biomass by white-rot fungi has been an important research topic. However, few simulated in-situ analyses have been conducted to uncover the decay.MethodsIn this study, the white-rot Lentinula edodes was used to colonize the wood and non-wood substrates, and then hyphal transcriptional response and substrate degradation were analyzed during the spatial-temporal colonization on different type substrates to better understand the depolymerization of lignocellulose.Results and discussionFaster growth and thicker mat of hyphae on corn stalk were observed in comparison to oak wafer. Coincide with the higher levels of gene transcripts related to protein synthesis on corn stalk. The higher lignin oxidase activity of hyphae was detected on oak wafer, and the higher cellulase activity was observed on corn stalk containing a much higher content of soluble sugars. A large number of carbohydrate-binding module (CBM1 and CBM20)-containing enzyme genes, including lytic polysaccharide monooxygenase (AA9), cellobiohydrolase (GH6 and GH7), glucanase (GH5), xylanase (GH10 and GH11), glucoamylase (GH15), and alpha-amylase (GH13), were significantly upregulated in the back-distal hyphae colonized on corn stalk. The hyphae tended to colonize and degrade the secondary cell wall, and the deposited oxalate crystal suggested that oxalate may play an important role during lignocellulose degradation. In addition, lignin was degraded in priority in oak wafer. Of note, three lignin monomers were degraded simultaneously in oak wafer but sequentially in corn stalk. This growth Our results indicated that the white-rot degradation pattern of lignocellulose is determined by the chemical composition and structure of the colonized biomass.