Temperature Modulates the Secretome of the Phytopathogenic Fungus Lasiodiplodia theobromae

Exploring the Phylogenetic Diversity of Botryosphaeriaceae and Diaporthe Species Causing Dieback and Shoot Blight of Blueberry in Serbia

Identifying the precise pathogens responsible for specific plant diseases is imperative for implementing targeted and efficient interventions and mitigating their spread. Dieback and shoot blight significantly diminish the lifespan and productivity of blueberries, yet the causative agents remain largely unidentified. To determine the identity and prevalence of the causal agents of branch dieback and shoot blight, we conducted multiyear and multisite sampling of diseased highbush blueberries (Vaccinium corymbosum cultivar Duke) in Serbia. Sixty-nine monosporic isolates were collected and characterized based on morphological, physiological features and multilocus phylogenetic analysis of internal transcribed spacer, β-tubulin, and translation elongation factor 1-α sequence data. Five species were identified as causal agents: Diaporthe eres (36 isolates), D. foeniculina (3 isolates), Neopestalotiopsis vaccinii (9 isolates), Neopestalotiopsis rosae (6 isolates), and Neofusicoccum parvum (15 isolates). The results of the pathogenicity tests performed with the 23 representative isolates confirmed the role of these species as primary pathogens in causing dieback and shoot blight of blueberry, with Neofusicoccum parvum being the most aggressive and D. eres the least. Our study underscores the diversity of genera and species of ascomycetes capable of causing blueberry dieback and shoot blight. Furthermore, our findings indicate that the agents responsible for the disease in Serbia differ from those identified in other regions worldwide.

The plant disease triangle facing climate change: a molecular perspective

Variations in climate conditions can dramatically affect plant health and the generation of climate-resilient crops is imperative to food security. In addition to directly affecting plants, it is predicted that more severe climate conditions will also result in greater biotic stresses. Recent studies have identified climate-sensitive molecular pathways that can result in plants being more susceptible to infection under unfavorable conditions. Here, we review how expected changes in climate will impact plant-pathogen interactions, with a focus on mechanisms regulating plant immunity and microbial virulence strategies. We highlight the complex interactions between abiotic and biotic stresses with the goal of identifying components and/or pathways that are promising targets for genetic engineering to enhance adaptation and strengthen resilience in dynamically changing environments.

Botryosphaeriaceae gene machinery: Correlation between diversity and virulence

The Botryosphaeriaceae family comprises numerous fungal pathogens capable of causing economically meaningful diseases in a wide range of crops. Many of its members can live as endophytes and turn into aggressive pathogens following the onset of environmental stress events. Their ability to cause disease may rely on the production of a broad set of effectors, such as cell wall-degrading enzymes, secondary metabolites, and peptidases. Here, we conducted comparative analyses of 41 genomes representing six Botryosphaeriaceae genera to provide insights into the genetic features linked to pathogenicity and virulence. We show that these Botryosphaeriaceae genomes possess a large diversity of carbohydrate-active enzymes (CAZymes; 128 families) and peptidases (45 families). Botryosphaeria, Neofusicoccum, and Lasiodiplodia presented the highest number of genes encoding CAZymes involved in the degradation of the plant cell wall components. The genus Botryosphaeria also exhibited the highest abundance of secreted CAZymes and peptidases. Generally, the secondary metabolites gene cluster profile was consistent in the Botryosphaeriaceae family, except for Diplodia and Neoscytalidium. At the strain level, Neofusicoccum parvum NpBt67 stood out among all the Botryosphaeriaceae genomes, presenting a higher number of secretome constituents. In contrast, the Diplodia strains showed the lowest richness of the pathogenicity- and virulence-related genes, which may correlate with their low virulence reported in previous studies. Overall, these results contribute to a better understanding of the mechanisms underlying pathogenicity and virulence in remarkable Botryosphaeriaceae species. Our results also support that Botryosphaeriaceae species could be used as an interesting biotechnological tool for lignocellulose fractionation and bioeconomy.

Unveiling the Secretome of the Fungal Plant Pathogen Neofusicoccum parvum Induced by In Vitro Host Mimicry

Neofusicoccum parvum is a fungal plant pathogen of a wide range of hosts but knowledge about the virulence factors of N. parvum and host-pathogen interactions is rather limited. The molecules involved in the interaction between N. parvum and Eucalyptus are mostly unknown, so we used a multi-omics approach to understand pathogen-host interactions. We present the first comprehensive characterization of the in vitro secretome of N. parvum and a prediction of protein-protein interactions using a dry-lab non-targeted interactomics strategy. We used LC-MS to identify N. parvum protein profiles, resulting in the identification of over 400 proteins, from which 117 had a different abundance in the presence of the Eucalyptus stem. Most of the more abundant proteins under host mimicry are involved in plant cell wall degradation (targeting pectin and hemicellulose) consistent with pathogen growth on a plant host. Other proteins identified are involved in adhesion to host tissues, penetration, pathogenesis, or reactive oxygen species generation, involving ribonuclease/ribotoxin domains, putative ricin B lectins, and necrosis elicitors. The overexpression of chitosan synthesis proteins during interaction with the Eucalyptus stem reinforces the hypothesis of an infection strategy involving pathogen masking to avoid host defenses. Neofusicoccum parvum has the molecular apparatus to colonize the host but also actively feed on its living cells and induce necrosis suggesting that this species has a hemibiotrophic lifestyle.

Distribution and Biodiversity of Seed-Borne Pathogenic and Toxigenic Fungi of Maize in Egypt and Their Correlations with Weather Variables

Studies of the biodiversity of plant pathogenic and toxigenic fungi are attracting great attention to improve the predictability of their epidemics and the development of their control programs. Two hundred maize grain samples were gathered from 25 maize-growing governorates in Egypt and 189 samples were processed for the isolation and identification of seed-borne fungal microbiome. Twenty-six fungal genera comprising 42 species were identified according to their morphological characteristics and ITS DNA sequence analysis. Occurrence and biodiversity indicators of these fungal species were calculated. Ustilago maydis, Alternaria alternata, Aspergillus flavus, A. niger, Penicillium spp., Cladosporium spp. and Fusarium verticillioides were the highly frequent (>90% for each), recording the highest relative abundance (˃50%). Al-Menia governorate showed the highest species diversity and richness, followed by Sohag, Al-Nobaria and New Valley governorates. Correlations of 18 fungal species with temperature, relative humidity, precipitation, wind speed, and solar radiation were analyzed using canonical correspondence analysis. Results showed that relative humidity, temperature, and wind speed, respectively, were the most impactful weather variables. However, the occurrence and distribution of these fungi were not clearly grouped into the distinctive climatic regions in which maize crops are grown. Monitoring the occurrence and distribution of the fungal pathogens of maize grains in Egypt will play an important role in predicting their outbreaks and developing appropriate future management strategies. The findings in this study may be useful to other maize-growing countries that have similar climatic conditions.

A Case Study in Saudi Arabia: Biodiversity of Maize Seed-Borne Pathogenic Fungi in Relation to Biochemical, Physiological, and Molecular Characteristics

Microbiodiversity is usually correlated with environmental conditions. This investigation is a case study to cover the lack of knowledge on the correlation of biochemical, physiological, and molecular attributes with the distribution of seed-borne pathogenic fungi of maize under the environmental conditions of the Kingdom of Saudi Arabia to help forecast any destructive epidemics. Forty-one fungal species belonging to 24 genera were detected using standard moist blotter (SMB), deep freezing blotter (DFB), and agar plate (AP) techniques. SMB was superior in detecting the maximum numbers (36 species) of seed-borne mycoflora. The pathogenicity assay revealed that, among 18 seed-borne fungal pathogens used, 12 isolates caused high percentages of rotted seeds and seedling mortality symptoms, which were identified molecularly using an internal transcribed spacer sequence. Two Curvularia spp. and Sarocladium zeae were reported for the first time in KSA. The strains showed various enzymatic activities and amino acid profiles under different environmental setups. Temperature and humidity were the environmental variables influencing the fungal pathogenicity. The highest pathogenicity was correlated with the presence and concentration of threonine, alanine, glutamic, aspartic acids, and protein. The study concluded with the discovery of four new phytopathogens in KSA and, further, evidenced a marked correlation among the investigated variables. Nevertheless, more studies are encouraged to include additional physiological properties of the phytopathogens, such as toxigenic activity, as well as extend the fungal biodiversity study to other plants.

Comparative Genomics Reveals Evolutionary Traits, Mating Strategies, and Pathogenicity-Related Genes Variation of Botryosphaeriaceae

Botryosphaeriaceae, as a major family of the largest class of kingdom fungi Dothideomycetes, encompasses phytopathogens, saprobes, and endophytes. Many members of this family are opportunistic phytopathogens with a wide host range and worldwide geographical distribution, and can infect many economically important plants, including food crops and raw material plants for biofuel production. To date, however, little is known about the family evolutionary characterization, mating strategies, and pathogenicity-related genes variation from a comparative genome perspective. Here, we conducted a large-scale whole-genome comparison of 271 Dothideomycetes, including 19 species in Botryosphaeriaceae. The comparative genome analysis provided a clear classification of Botryosphaeriaceae in Dothideomycetes and indicated that the evolution of lifestyle within Dothideomycetes underwent four major transitions from non-phytopathogenic to phytopathogenic. Mating strategies analysis demonstrated that at least 3 transitions were found within Botryosphaeriaceae from heterothallism to homothallism. Additionally, pathogenicity-related genes contents in different genera varied greatly, indicative of genus-lineage expansion within Botryosphaeriaceae. These findings shed new light on evolutionary traits, mating strategies and pathogenicity-related genes variation of Botryosphaeriaceae.

Combining an HA + Cu (II) Site-Targeted Copper-Based Product with a Pruning Wound Protection Program to Prevent Infection with Lasiodiplodia spp. in Grapevine

The genus Lasiodiplodia has been reported from several grape growing regions and is considered as one of the fastest wood colonizers, causing Botryosphaeria dieback. The aim of this study was to (i) evaluate the efficacy of Esquive®, a biocontrol agent, on vineyard pruning wound protection, applied single or, in a combined protection strategy with a new site-targeted copper-based treatment (LC2017), and (ii) compare their efficacy with chemical protection provided by the commercially available product, Tessior®. For two seasons, protectants were applied onto pruning wounds, while LC2017 was applied throughout the season according to the manufacturer's instructions. Pruning wounds of two different cultivars were inoculated with three isolates of Lasiodiplodia spp. Efficacy of the wound protectants, varied between both years of the assay and according to the cultivar studied but were able to control the pathogen to some extent. The application of LC2017 did not show clear evidence of improving the control obtained by the sole application of the other products tested. Nevertheless, LC2017 showed a fungistatic effect against Lasiodiplodia spp., in vitro, and has previously shown an elicitor effect against grapevine trunk diseases. Therefore, this combination of two protection strategies may constitute a promising long-term approach to mitigate the impact of Botryosphaeria dieback.

Biodiversity of Pathogenic and Toxigenic Seed-Borne Mycoflora of Wheat in Egypt and Their Correlations with Weather Variables

Surveillance investigations for pathogenic and toxigenic fungi are important to refine our understanding of their epidemiology and help in predicting their outbreaks. During 2019, 198 samples of wheat grains were collected from 25 wheat-growing governorates in Egypt to detect and identify seed-borne mycoflora in vitro. Forty-four fungal species belonging to 20 genera were identified. Molecular data for these fungi were analyzed to construct a phylogenetic tree. Occurrence and biodiversity indicators were calculated. Two prevalent pathogens (average incidence > 40%) were Alternaria alternata and Cladosporium spp. Ustilago tritici was present in only seven of the 25 governorates, and less abundant than Tilletia tritici, the causal agent of stinking smut. Sinai governorate recorded the greatest species diversity, while the greatest species richness was in Qena and Sohag governorates. Canonical correspondence analysis of data for 20 fungal genera with temperature, relative humidity, precipitation, wind speed or solar radiation revealed that relative humidity was the most influential weather variable. It showed that occurrence and distribution of the 20 genera corresponded well with three out of four Egyptian climatic regions: Mediterranean, semi-arid, and arid. Knowing pathogen occurrence and distribution in Egypt is the first step to developing future disease management strategies to limit yield losses and improve food security. Despite this study being conducted on the wheat-growing areas in Egypt, our findings are useful for other wheat-growing countries that share the same climatic conditions. The correlation between a given fungus and the climatic variables can be useful in other ecosystems.

Speaking the language of lipids: the cross-talk between plants and pathogens in defence and disease

Lipids and fatty acids play crucial roles in plant immunity, which have been highlighted over the past few decades. An increasing number of studies have shown that these molecules are pivotal in the interactions between plants and their diverse pathogens. The roles played by plant lipids fit in a wide spectrum ranging from the first physical barrier encountered by the pathogens, the cuticle, to the signalling pathways that trigger different immune responses and expression of defence-related genes, mediated by several lipid molecules. Moreover, lipids have been arising as candidate biomarkers of resistance or susceptibility to different pathogens. Studies on the apoplast and extracellular vesicles have been highlighting the possible role of lipids in the intercellular communication and the establishment of systemic acquired resistance during plant-pathogen interactions. From the pathogen perspective, lipid metabolism and specific lipid molecules play pivotal roles in the pathogen's life cycle completion, being crucial during recognition by the plant and evasion from the host immune system, therefore potentiating infection. Studies conducted in the last years have contributed to a better understanding of the language of lipids during the cross-talk between plants and pathogens. However, it is essential to continue exploring the knowledge brought up to light by transcriptomics and proteomics studies towards the elucidation of lipid signalling processes during defence and disease. In this review, we present an updated overview on lipids associated to plant-pathogen interactions, exploiting their roles from the two sides of this battle.

What Do We Know about Botryosphaeriaceae? An Overview of a Worldwide Cured Dataset

Botryosphaeriaceae-related diseases occur worldwide in a wide variety of plant hosts. The number of studies targeting the distribution, diversity, ecology, and pathogenicity of Botryosphaeriaceae species are consistently increasing. However, with the lack of consistency in species delimitation, the name of hosts, and the locations of studies, it is almost impossible to quantify the presence of these species worldwide, or the number of different host–fungus interactions that occur. In this review, we collected and organized Botryosphaeriaceae occurrences in a single cured dataset, allowing us to obtain for the first time a complete perspective on species’ global diversity, dispersion, host association, ecological niches, pathogenicity, communication efficiency of new occurrences, and new host–fungus associations. This dataset is freely available through an interactive and online application. The current release (version 1.0) contains 14,405 cured isolates and 2989 literature references of 12,121 different host–fungus interactions with 1692 different plant species from 149 countries.

Effect of γ-Aminobutyric Acid (GABA) on the Metabolome of Two Strains of Lasiodiplodia theobromae Isolated from Grapevine

The effect of γ-aminobutyric acid (GABA) on the metabolome of two strains of Lasiodiplodia theobromae isolated from grapevine that hold a different degree of virulence to the host plant (LA-SOL3 (more virulent), LA-SV1 (less virulent)) was investigated. The culture filtrates and crude extracts from the two strains grown in the presence and absence of 10 mM of GABA were tested for phytotoxicity on tomato plant cuttings and leaves, respectively. Considering the opportunistic nature of this fungus for humans, crude extracts were also tested for cytotoxicity on mammalian cell lines. We found that culture filtrates and crude extracts have a decreased toxicity in the presence of GABA. Metabolomic analysis, conducted on both strains at both growth conditions, revealed the production of several compounds, such as indole-3-carboxylic acid (ICA, which is the main compound produced by L. theobromae), 3-indolecarboxyaldehyde, (3R,4S)-botryodiplodin, (R)-mellein. Finally, data demonstrate that GABA both induces a decrease in the amount of ICA, and a diversification of the metabolites produced by L. theobromae.

Toxicity of Recombinant Necrosis and Ethylene-Inducing Proteins (NLPs) from Neofusicoccum parvum

Neofusicoccum parvum is a fungal pathogen associated with a wide range of plant hosts. Despite being widely studied, the molecular mechanism of infection of N. parvum is still far from being understood. Analysis of N. parvum genome lead to the identification of six putative genes encoding necrosis and ethylene-inducing proteins (NLPs). The sequence of NLPs genes (NprvNep 1-6) were analyzed and four of the six NLP genes were successfully cloned, expressed in E. coli and purified by affinity chromatography. Pure recombinant proteins were characterized according to their phytotoxic and cytotoxic effects to tomato leaves and to mammalian Vero cells, respectively. These assays revealed that all NprvNeps tested are cytotoxic to Vero cells and also induce cell death in tomato leaves. NprvNep2 was the most toxic to Vero cells, followed by NprvNep1 and 3. NprvNep4 induced weaker, but, nevertheless, still significant toxic effects to Vero cells. A similar trend of toxicity was observed in tomato leaves: the most toxic was NprvNep 2 and the least toxic NprvNep 4. This study describes for the first time an overview of the NLP gene family of N. parvum and provides additional insights into its pathogenicity mechanism.

Effect of temperature on the phytotoxicity and cytotoxicity of Botryosphaeriaceae fungi

Botryosphaeriaceae fungi are phytopathogens and human opportunists. The influence of temperature on the phytotoxicity and cytotoxicity of culture filtrates of five Botryosphaeriaceae species was investigated. All culture filtrates of fungi grown at 25 °C were phytotoxic: symptoms were evaluated based on visual inspection of necrosis areas and on the maximum quantum yield of photosystem II, F_v/F_m. Diplodiacorticola and Neofusicoccum kwambonambiense were the most phytotoxic, followed by Neofusicoccum parvum CAA704 and Botryosphaeria dothidea. Phytotoxicity dramatically decreased when strains were grown at 37 °C, except for B. dothidea. All strains, except N. parvum CAA366 and Neofusicoccum eucalyptorum, grown either at 25 °C or 37 °C, were toxic to mammalian cells; at 25 °C and at 37°C, D. corticola and B. dothidea were the most cytotoxic, respectively. Although the toxicity of B. dothidea to both cell lines and of N. kwambonambiense to Vero cells increased with temperature, the opposite was found for the other species tested. Our results suggest that temperature modulates the expression of toxic compounds that, in a scenario of a global increase of temperature, may contribute to new plant infections but also human infections, especially in the case of B. dothidea.

Botryosphaeriaceae Fungi as Causal Agents of Dieback and Corky Bark in Rambutan and Longan

Fungi in the Botryosphaeriaceae family cause dieback, fruit rots, and stem cankers in many tropical fruit trees. To identify which species of Botryosphaeriaceae were present in tropical fruit in Puerto Rico and the symptoms they cause in rambutan and longan, a disease survey was conducted throughout the island from 2008 to 2016. Diseased organs of rambutan, longan, mango, and tangerine were collected and 39 isolates belonging to the Botryosphaeriaceae family were isolated and identified. Phylogenetic analysis of three nuclear genes identified nine species: six Lasiodiplodia spp. and three Neofusicoccum spp. All 39 isolates were inoculated on healthy 1-year-old rambutan and longan seedlings to confirm their pathogenicity. Dieback on both rambutan and longan was observed at 14 days after inoculation (DAI). Fourteen isolates from seven Botryosphaeriaceae species (Lasiodiplodia brasiliensis, L. hormozganensis, L. iraniensis, L. pseudotheobromae, L. theobromae, Neofusicoccum batangarum, and N. parvum) caused dieback in rambutan. Five of these pathogenic isolates were collected from rambutan, four from longan, two from mango, and three from tangerine. Ten isolates of four Lasiodiplodia spp. caused dieback in longan: L. hormozganensis, L. iraniensis, L. pseudotheobromae and L. theobromae,. Of these, three were collected from rambutan, three from longan, one from mango, and three from tangerine. Abundant development of pycnidia on branches, called corky bark, were observed on both rambutan and longan 60 DAI. Cross-inoculations showed that pathogenicity is wide in spectrum, indicating that different planting alternatives should be considered for better crop management.

Dual RNA Sequencing of Vitis vinifera during Lasiodiplodia theobromae Infection Unveils Host-Pathogen Interactions

Lasiodiplodia theobromae is one of the most aggressive agents of the grapevine trunk disease Botryosphaeria dieback. Through a dual RNA-sequencing approach, this study aimed to give a broader perspective on the infection strategy deployed by L. theobromae, while understanding grapevine response. Approximately 0.05% and 90% of the reads were mapped to the genomes of L. theobromae and Vitis vinifera, respectively. Over 2500 genes were significantly differentially expressed in infected plants after 10 dpi, many of which are involved in the inducible defense mechanisms of grapevines. Gene expression analysis showed changes in the fungal metabolism of phenolic compounds, carbohydrate metabolism, transmembrane transport, and toxin synthesis. These functions are related to the pathogenicity mechanisms involved in plant cell wall degradation and fungal defense against antimicrobial substances produced by the host. Genes encoding for the degradation of plant phenylpropanoid precursors were up-regulated, suggesting that the fungus could evade the host defense response using the phenylpropanoid pathway. The up-regulation of many distinct components of the phenylpropanoid pathway in plants supports this hypothesis. Moreover, genes related to phytoalexin biosynthesis, hormone metabolism, cell wall modification enzymes, and pathogenesis-related proteins seem to be involved in the host responses observed. This study provides additional insights into the molecular mechanisms of L. theobromae and V. vinifera interactions.

A multi-omics analysis of the grapevine pathogen Lasiodiplodia theobromae reveals that temperature affects the expression of virulence- and pathogenicity-related genes

Lasiodiplodia theobromae (Botryosphaeriaceae, Ascomycota) is a plant pathogen and human opportunist whose pathogenicity is modulated by temperature. The molecular effects of temperature on L. theobromae are mostly unknown, so we used a multi-omics approach to understand how temperature affects the molecular mechanisms of pathogenicity. The genome of L. theobromae LA-SOL3 was sequenced (Illumina MiSeq) and annotated. Furthermore, the transcriptome (Illumina TruSeq) and proteome (Orbitrap LC-MS/MS) of LA-SOL3 grown at 25 °C and 37 °C were analysed. Proteins related to pathogenicity (plant cell wall degradation, toxin synthesis, mitogen-activated kinases pathway and proteins involved in the velvet complex) were more abundant when the fungus grew at 25 °C. At 37 °C, proteins related to pathogenicity were less abundant than at 25 °C, while proteins related to cell wall organisation were more abundant. On the other hand, virulence factors involved in human pathogenesis, such as the SSD1 virulence protein, were expressed only at 37 °C. Taken together, our results showed that this species presents a typical phytopathogenic molecular profile that is compatible with a hemibiotrophic lifestyle. We showed that L. theobromae is equipped with the pathogenesis toolbox that enables it to infect not only plants but also animals.

Grapevine trunk diseases under thermal and water stresses

Heat and water stresses, individually or combined, affect both the plant (development, physiology, and production) and the pathogens (growth, morphology, dissemination, distribution, and virulence). The grapevine response to combined abiotic and biotic stresses is complex and cannot be inferred from the response to each single stress. Several factors might impact the response and the recovery of the grapevine, such as the intensity, duration, and timing of the stresses. In the heat/water stress-GTDs-grapevine interaction, the nature of the pathogens, and the host, i.e., the nature of the rootstock, the cultivar and the clone, has a great importance. This review highlights the lack of studies investigating the response to combined stresses, in particular molecular studies, and the misreading of the relationship between rootstock and scion in the relationship GTDs/abiotic stresses. Grapevine trunk diseases (GTDs) are one of the biggest threats to vineyard sustainability in the next 30 years. Although many treatments and practices are used to manage GTDs, there has been an increase in the prevalence of these diseases due to several factors such as vineyard intensification, aging vineyards, or nursery practices. The ban of efficient treatments, i.e., sodium arsenite, carbendazim, and benomyl, in the early 2000s may be partly responsible for the fast spread of these diseases. However, GTD-associated fungi can act as endophytes for several years on, or inside the vine until the appearance of the first symptoms. This prompted several researchers to hypothesise that abiotic conditions, especially thermal and water stresses, were involved in the initiation of GTD symptoms. Unfortunately, the frequency of these abiotic conditions occurring is likely to increase according to the recent consensus scenario of climate change, especially in wine-growing areas. In this article, following a review on the impact of combined thermal and water stresses on grapevine physiology, we will examine (1) how this combination of stresses might influence the lifestyle of GTD pathogens, (2) learnings from grapevine field experiments and modelling aiming at studying biotic and abiotic stresses, and (3) what mechanistic concepts can be used to explain how these stresses might affect the grapevine plant status.

Secretomic analysis of Beauveria bassiana related to cattle tick, Rhipicephalus microplus, infection

Beauveria bassiana is widely studied as an alternative to chemical acaricides in controlling the cattle tick Rhipicephalus microplus. Although its biocontrol efficiency has been proved in laboratory and field scales, there is a need to a better understanding of host interaction process at molecular level related to biocontrol activity. In this work, applying a proteomic technique multidimensional protein identification technology (MudPIT), the differential secretome of B. bassiana induced by the host R. microplus cuticle was evaluated. The use of the host cuticle in a culture medium, mimicking an infection condition, is an established experimental model that triggers the secretion of inducible enzymes. From a total of 236 proteins, 50 proteins were identified exclusively in infection condition, assigned to different aspects of infection like host adhesion, cuticle penetration and fungal defense, and stress. Other 32 proteins were considered up- or down-regulated. In order to get a meaningful global view of the secretome, several bioinformatic analyses were performed. Regarding molecular function classification, the highest number of proteins in the differential secretome was assigned in to hydrolase activity, enzyme class of all cuticle-degrading enzymes like lipases and proteases. These activities were also further validated through enzymatic assays. The results presented here reveal dozens of specific proteins and different processes potentially implicated in cattle tick infection improving the understanding of molecular basis of biocontrol of B. bassiana against R. microplus.

Production of toxic metabolites by two strains of Lasiodiplodia theobromae, isolated from a coconut tree and a human patient

Lasiodiplodia theobromae is a phytopathogenic fungus that causes diseases not only in a broad number of plant hosts but also occasionally in humans. The capacity of L. theobromae to produce bioactive metabolites at 25 C (environmental mean temperature) and at 37 C (body mean temperature) was investigated. Two strains, CAA019 and CBS339.90, isolated respectively from a coconut tree and a human patient were characterized. The phytotoxicity and cytotoxicity (on mammalian cells) of the secretomes of both strains of L. theobromae were investigated. Also, phytotoxicity and cytotoxicity of pure compounds were evaluated. The phytotoxicity of the secretome of strain CAA019 was higher than the phytotoxicity of the secretome of strain CBS339.90 at 25 C. However, the phytotoxicity for both strains decreased when they were grown at 37 C. Only the secretome of strain CBS339.90 grown at 37 C induced up to 90% Vero and 3T3 cell mortality. This supports the presence of different metabolites in the secretome of strains CAA019 and CBS339.90. Metabolites typical of L. theobromae were isolated and identified from organic extracts of the secretome of both strains (e.g., 3-indolecarboxylic acid, jasmonic acid, lasiodiplodin, four substituted 2-dihydrofuranones, two melleins, and cyclo-(Trp-Ala)). Also, metabolites such as scytalone, not previously reported for this species, were isolated and identified. Metabolite production is affected by strain and temperature. In fact, some metabolites are strain specific (e.g., lasiodiplodin) and some metabolites are temperature specific (e.g., jasmonic acid). Although more strains should be characterized, it may be anticipated that temperature tuning of secondary-metabolite production emerges as a putative contributing factor in the modulation of L. theobromae pathogenicity towards plants, and also towards mammalian cells.

Secretome Analysis Identifies Potential Pathogenicity/Virulence Factors of Tilletia indica, a Quarantined Fungal Pathogen Inciting Karnal Bunt Disease in Wheat

Tilletia indica is a smut fungus that incites Karnal bunt in wheat. It has been considered as quarantine pest in more than 70 countries. Despite its quarantine significance, there is meager knowledge regarding the molecular mechanisms of disease pathogenesis. Moreover, various disease management strategies have proven futile. Development of effective disease management strategy requires identification of pathogenicity/virulence factors. With this aim, the present study was conducted to compare the secretomes of T. indica isolates, that is, highly (TiK) and low (TiP) virulent isolates. About 120 and 95 protein spots were detected reproducibly in TiK and TiP secretome gel images. Nineteen protein spots, which were consistently observed as upregulated/differential in the secretome of TiK isolate, were selected for their identification by MALDI-TOF/TOF. Identified proteins exhibited homology with fungal proteins playing important role in fungal adhesion, penetration, invasion, protection against host-derived reactive oxygen species, production of virulence factors, cellular signaling, and degradation of host cell wall proteins and antifungal proteins. These results were complemented with T. indica genome sequence leading to identification of candidate pathogenicity/virulence factors homologs that were further subjected to sequence- and structure-based functional annotation. Thus, present study reports the first comparative secretome analysis of T. indica for identification of pathogenicity/virulence factors. This would provide insights into pathogenic mechanisms of T. indica and aid in devising effective disease management strategies.

Lasiodiplodia theobromae as a Producer of Biotechnologically Relevant Enzymes

Phytopathogenic fungi are known to produce several types of enzymes usually involved in plant cell wall degradation and pathogenesis. The increasing of global temperature may induce fungi, such as Lasiodiplodia theobromae (L. theobromae), to alter its behavior. Nonetheless, there is only limited information regarding the effect of temperature on L. theobromae production of enzymes. The need for new, thermostable enzymes, that are biotechnologically relevant, led us to investigate the effect of temperature on the production of several extracellular enzymatic activities by different L. theobromae strains. Fungi were grown at 25 °C, 30 °C and 37 °C and the enzymatic activities were detected by plate assays, quantified by spectrophotometric methods and characterized by zymography. The thermostability (25–80 °C) of the enzymes produced was also tested. Strains CAA019, CBS339.90, LA-SOL3, LA-SV1 and LA-MA-1 produced amylases, gelatinases, caseinases, cellulases, lipases, laccases, xylanases, pectinases and pectin liases. Temperature modulated the expression of the enzymes, and this effect was more visible when fungi were grown at 37 °C than at lower temperatures. Contrary to proteolytic and endoglucanolytic activities, whose highest activities were detected when fungi were grown at 30 °C, lipolytic activity was not detected at this growth temperature. Profiles of proteases and endoglucanases of fungi grown at different temperatures were characterized by zymography. Enzymes were shown to be more thermostable when fungi were grown at 30 °C. Proteases were active up to 50 °C and endoglucanases up to 70 °C. Lipases were the least stable, with activities detected up to 45 °C. The enzymatic profiles detected for L. theobromae strains tested showed to be temperature and strain-dependent, making this species a good target for biotechnological applications.