MoIVD-Mediated Leucine Catabolism Is Required for Vegetative Growth, Conidiation and Full Virulence of the Rice Blast Fungus Magnaporthe oryzae

MoJMJD6, a Nuclear Protein, Regulates Conidial Germination and Appressorium Formation at the Early Stage of Pathogenesis in Magnaporthe oryzae

In plant-pathogen interactions, Magnaporthe oryzae causes blast disease on more than 50 species of 14 monocot plants, including important crops such as rice, millet, and most 15 recently wheat. M. oryzae is a model fungus for studying plant-microbe interaction, and the main source for fungal pathogenesis in the field. Here we report that MoJMJD6 is required for conidium germination and appressorium formation in M. oryzae. We obtained MoJMJD6 mutants (ΔMojmjd6) using a target gene replacement strategy. The MoJMD6 deletion mutants were delayed for conidium germination, glycogen, and lipid droplets utilization and consequently had decreased virulence. In the ΔMojmjd6 null mutants, global histone methyltransferase modifications (H3K4me3, H3K9me3, H3K27me3, and H3K36me2/3) of the genome were unaffected. Taken together, our results indicated that MoJMJD6 function as a nuclear protein which plays an important role in conidium germination and appressorium formation in the M. oryzae. Our work provides insights into MoJMJD6-mediated regulation in the early stage of pathogenesis in plant fungi.

Branched chain amino acids catabolism as a source of new drug targets in pathogenic protists

Leucine, isoleucine, and valine, collectively termed Branched Chain Amino Acids (BCAA), are hydrophobic amino acids (AAs) and are essential for most eukaryotes since in these organisms they cannot be biosynthesized and must be supplied by the diet. These AAs are structurally relevant for muscle cells and, of course, important for the protein synthesis process. The metabolism of BCAA and its participation in different biological processes in mammals have been relatively well described. However, for other organisms as pathogenic parasites, the literature is really scarce. Here we review the BCAA catabolism, compile evidence on their relevance for pathogenic eukaryotes with special emphasis on kinetoplastids and highlight unique aspects of this underrated pathway.

Transcriptome Analysis of Protein Kinase MoCK2, which Affects Acetyl-CoA Metabolism and Import of CK2-Interacting Mitochondrial Proteins into Mitochondria in the Rice Blast Fungus Magnaporthe oryzae

The rice pathogen Magnaporthe oryzae causes severe losses to rice production. Previous studies have shown that the protein kinase MoCK2 is essential for pathogenesis, and this ubiquitous eukaryotic protein kinase might affect several processes in the fungus that are needed for infection. To better understand which cellular processes are affected by MoCK2 activity, we performed a detailed transcriptome sequencing analysis of deletions of the MoCK2 b1 and b2 components in relation to the background strain Ku80 and connected this analysis with the abundance of substrates for proteins in a previous pulldown of the essential CKa subunit of CK2 to estimate the effects on proteins directly interacting with CK2. The results showed that MoCK2 seriously affected carbohydrate metabolism, fatty acid metabolism, amino acid metabolism, and the related transporters and reduced acetyl-CoA production. CK2 phosphorylation can affect the folding of proteins and especially the effective formation of protein complexes by intrinsically disordered or mitochondrial import by destabilizing soluble alpha helices. The upregulated genes found in the pulldown of the b1 and b2 mutants indicate that proteins directly interacting with CK2 are compensatorily upregulated depending on their pulldown. A similar correlation was found for mitochondrial proteins. Taken together, the classes of proteins and the changes in regulation in the b1 and b2 mutants suggest that CK2 has a central role in mitochondrial metabolism, secondary metabolism, and reactive oxygen species (ROS) resistance, in addition to its previously suggested role in the formation of new ribosomes, all of which are processes central to efficient nonself responses as innate immunity. IMPORTANCE The protein kinase CK2 is highly expressed and essential for plants, animals, and fungi, affecting fatty acid-related metabolism. In addition, it directly affects the import of essential mitochondrial proteins into mitochondria. These effects mean that CK2 is essential for lipid metabolism and mitochondrial function and, as shown previously, is crucial for making new translation machinery proteins. Taken together, our new results combined with previously reported results indicate that CK2 is an essential protein necessary for the capacities to launch efficient innate immunity responses and withstand the negative effects of such responses necessary for general resistance against invading bacteria and viruses as well as to interact with plants, withstand plant immunity responses, and kill plant cells.

Characterization of two infection-induced transcription factors of Magnaporthe oryzae reveals their roles in regulating early infection and effector expression

The initial stage of rice blast fungus, Magnaporthe oryzae, infection, before 36 h postinoculation, is a critical timespan for deploying pathogen effectors to overcome the host's defences and ultimately cause the disease. However, how this process is regulated at the transcription level remains largely unknown. This study functionally characterized two M. oryzae Early Infection-induced Transcription Factor genes (MOEITF1 and MOEITF2) and analysed their roles in this process. Target gene deletion and mutant phenotype analysis showed that the mutants Δmoeitf1 and Δmoeitf2 were only defective for infection growth but not for vegetative growth, asexual/sexual sporulation, conidial germination, and appressoria formation. Gene expression analysis of 30 putative effectors revealed that most effector genes were down-regulated in mutants, implying a potential regulation by the transcription factors. Artificial overexpression of two severely down-regulated effectors, T1REP and T2REP, in the mutants partially restored the pathogenicity of Δmoeitf1 and Δmoeitf2, respectively, indicating that these are directly regulated. Yeast one-hybrid assay and electrophoretic mobility shift assay indicated that Moeitf1 specifically bound the T1REP promoter and Moeitf2 specifically bound the T2REP promoter. Both T1REP and T2REP were predicted to be secreted during infection, and the mutants of T2REP were severely reduced in pathogenicity. Our results indicate crucial roles for the fungal-specific Moeitf1 and Moeitf2 transcription factors in regulating an essential step in M. oryzae early establishment after penetrating rice epidermal cells, highlighting these as possible targets for disease control.

Mining the Flavoproteome of Brucella ovis, the Brucellosis Causing Agent in Ovis aries

Flavoproteins are a diverse class of proteins that are mostly enzymes and contain as cofactors flavin mononucleotide (FMN) and/or flavin adenine dinucleotide (FAD), which enable them to participate in a wide range of physiological reactions. We have compiled 78 potential proteins building the flavoproteome of Brucella ovis (B. ovis), the causative agent of ovine brucellosis. The curated list of flavoproteins here reported is based on (i) the analysis of sequence, structure and function of homologous proteins, and their classification according to their structural domains, clans, and expected enzymatic functions; (ii) the constructed phylogenetic trees of enzyme functional classes using 19 Brucella strains and 26 pathogenic and/or biotechnological relevant alphaproteobacteria together with B. ovis; and (iii) the evaluation of the genetic context for each entry. Candidates account for ∼2.7% of the B. ovis proteome, and 75% of them use FAD as cofactor. Only 55% of these flavoproteins belong to the core proteome of Brucella and contribute to B. ovis processes involved in maintenance activities, survival and response to stress, virulence, and/or infectivity. Several of the predicted flavoproteins are highly divergent in Brucella genus from revised proteins and for them it is difficult to envisage a clear function. This might indicate modified catalytic activities or even divergent processes and mechanisms still not identified. We have also detected the lack of some functional flavoenzymes in B. ovis, which might contribute to it being nonzoonotic. Finally, potentiality of B. ovis flavoproteome as the source of antimicrobial targets or biocatalyst is discussed. IMPORTANCE Some microorganisms depend heavily on flavin-dependent activities, but others maintain them at a minimum. Knowledge about flavoprotein content and functions in different microorganisms will help to identify their metabolic requirements, as well as to benefit either industry or health. Currently, most flavoproteins from the sheep pathogen Brucella ovis are only automatically annotated in databases, and only two have been experimentally studied. Indeed, certain homologues with unknown function are not characterized, and they might relate to still not identified mechanisms or processes. Our research has identified 78 members that comprise its flavoproteome, 76 of them flavoenzymes, which mainly relate to bacteria survival, virulence, and/or infectivity. The list of flavoproteins here presented allows us to better understand the peculiarities of Brucella ovis and can be applied as a tool to search for candidates as new biocatalyst or antimicrobial targets.

Metabolite profiling reveals overexpression of the global regulator, MoLAEA leads to increased synthesis of metabolites in Magnaporthe oryzae

AIMS

To study the altered metabolic pathways and metabolites produced in overexpression and knockdown mutants of a global regulator named MoLAEA, which was recently found to regulate the expression of the genes involved in secondary metabolism in one of the most destructive plant pathogens, Magnaporthe oryzae.

METHODS AND RESULTS

Mass spectrometry-based global untargeted metabolomic profiling was used to identify altered metabolites. Metabolites were extracted from the mutant strains of MoLAEA using two extraction methods viz., aqueous and organic extraction and data acquired using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in positive and negative polarities. Levels of metabolites involved in various biological pathways such as amino acid as well as polyamine biosynthesis, fatty acid and pyrimidine metabolism showed remarkable change in the mutant strains. Interestingly, metabolites involved in stress responses were produced in higher quantities in the overexpression strain whereas, certain overproduced metabolites were associated with distinctive phenotypic changes in the overexpression strain compared to the wild-type. Further, the expression of several genes involved in the stress responses was found to have higher expression in the overexpression strain.

CONCLUSIONS

The global regulator MoLAEA is involved in secondary metabolism in the plant pathogen M. oryzae such that the mutant strains showed altered level of several metabolites involved in the biosynthesis pathways compared to the wild-type. Also, metabolites involved in stress responses were overproduced in the overexpression strain and this can be seen in the higher growth in media amended with stress-inducing agents or higher expression of genes involved in stress response in the overexpression strain compared to the wild-type.

SIGNIFICANCE AND IMPACT

This is the first report of metabolite profiling relative to the global regulation of secondary metabolism in M. oryzae, where secondary metabolism is poorly understood. It opens up avenues for more relevant investigations on the genetic regulation of several of the metabolites found in the analysis, which have not been previously characterized in M. oryzae.

Comparative Genomic Data Provide New Insight on the Evolution of Pathogenicity in Sporothrix Species

Sporothrix species are commonly isolated from environmental and clinical samples. As common causes of zoonotic mycosis, Sporothrix species may result in localized or disseminated infections, posing considerable threat to animal and human health. However, the pathogenic profiles of different Sporothrix species varied, in virulence, geographic location and host ranges, which have yet to be explored. Analysing the genomes of Sporothrix species are useful for understanding their pathogenicity. In this study, we analyzed the whole genome of 12 Sporothrix species and six S. globosa isolates from different clinical samples in China. By combining comparative analyses with Kyoto Encyclopedia of Genes and Genomes (KEGG), Carbohydrate-Active enZymes (CAZy), antiSMASH, Pfam, and PHI annotations, Sporothrix species showed exuberant primary and secondary metabolism processes. The genome sizes of four main clinical species, i.e., S. brasiliensis, S. schenckii, S. globosa, and S. luriei were significantly smaller than other environmental and clinical Sporothrix species. The contracted genes included mostly CAZymes and peptidases genes that were usually associated with the decay of plants, as well as the genes that were associated with the loss of pathogenicity and the reduced virulence. Our results could, to some extent, explain a habitat shift of Sporothrix species from a saprobic life in plant materials to a pathogenic life in mammals and the increased pathogenicity during the evolution. Gene clusters of melanin and clavaric acid were identified in this study, which improved our understanding on their pathogenicity and possible antitumor effects. Moreover, our analyses revealed no significant genomic variations among different clinical isolates of S. globosa from different regions in China.

2-Methoxy-1,4-naphthoquinone Induces Metabolic Shifts in Penicillium Digitatum Revealed by High-Dimensional Biological Data

Penicillium digitatum is the primary pathogen causing the green mold of citrus. The need for the development of higher effective and lower toxic natural antifungal agents is urgent, owing to the lack of antifungal agents that can successfully combat P. digitatum. Herein, the effects and mechanisms of 2-methoxy-1,4-naphthoquinone (MNQ) as a potential inhibitor of P. digitatumwere studied. First, MNQ showed a significant anti-P. digitatum effect with a minimum inhibitory concentration value of 5.0 μg/mL. Then, transcriptome, proteome, and metabolome profiling were performed on the MNQ-treated P. digitatum. A total of 910 genes, 297 proteins, and 174 metabolites changed significantly. The omics analysis indicated that it could be seen that MNQ mainly inhibits the growth of P. digitatum by affecting the synthesis of branched-chain amino acids and cell walls. These findings will be a great contribution to the further understanding of the possible molecular action of MNQ.

Cross-Species Functional Conservation and Possible Origin of the N-Terminal Specificity Domain of Mitochondrial Presequences

Plants have two endosymbiotic organelles, chloroplast and mitochondrion. Although they have their own genomes, proteome assembly in these organelles depends on the import of proteins encoded by the nuclear genome. Previously, we elucidated the general design principles of chloroplast and mitochondrial targeting signals, transit peptide, and presequence, respectively, which are highly diverse in primary structure. Both targeting signals are composed of N-terminal specificity domain and C-terminal translocation domain. Especially, the N-terminal specificity domain of mitochondrial presequences contains multiple arginine residues and hydrophobic sequence motif. In this study we investigated whether the design principles of plant mitochondrial presequences can be applied to those in other eukaryotic species. We provide evidence that both presequences and import mechanisms are remarkably conserved throughout the species. In addition, we present evidence that the N-terminal specificity domain of presequence might have evolved from the bacterial TAT (twin-arginine translocation) signal sequence.