The escalating global population has led to an increased demand for both quantity and quality in food production. Throughout history, plant diseases have posed significant threats to agricultural output by causing substantial food losses annually while also compromising product quality. Accurate identification of pathogens, clarifying the pathogenic mechanism of pathogens, and understanding the interaction between pathogens and hosts are important for the control of plant diseases. This Special Issue, “Research Progress on Pathogenicity of Fungi in Crops”, belongs to the section “Pest and Disease Management” of Agronomy. It contains research papers on the identification and phylogeny of fungal pathogens, the molecular genetics of plant fungal pathogens, the molecular mechanisms of fungal pathogenicity, and the molecular basis of the interaction between fungi and crops. These studies encapsulate efforts to understand disease systems within current genomics, transcriptomics, proteomics, and metabolomics studies, highlighting research findings that could be future targets for crop disease and pest control. The studies presented in this Special Issue promote the progress of fungal pathogenicity research in crops and provide a scientific basis for future disease control, which is of great significance for sustainable agricultural development and global food security.

Alternaria brown spot (ABS), caused by Alternaria alternata, is an economically important fungal disease of citrus worldwide. The ABS pathogen A. alternata tangerine pathotype can produce a host-specific ACT toxin, which is regulated by ACT toxin gene cluster located in the conditionally dispensable chromosome (CDC). Previously, we have assembled a draft genome of A. alternata tangerine pathotype strain Z7, which comprises 165 contigs. In this study, we report a chromosome-level genome assembly of A. alternata Z7 through the combination of Oxford Nanopore sequencing and Illumina sequencing technologies. The assembly of A. alternata Z7 had a total size of 34.28 Mb, with a GC content of 51.01% and contig N₅₀of 3.08 Mb. The genome is encompassed 12,067 protein-coding genes, 34 ribosomal RNAs, and 107 transfer RNAs. Interestingly, A. alternata Z7 is composed of 10 essential chromosomes and 2 CDCs, which is consistent with the experimental evidences of pulsed-field gel electrophoresis. To our best knowledge, this is the first chromosome-level genome assembly of A. alternata. In addition, a database for citrus-related Alternaria genomes has been established to provide public resources for the sequences, annotation and comparative genomics data of Alternaria spp. The improved genome sequence and annotation at the chromosome level is a significant step toward a better understanding of the pathogenicity of A. alternata. The database will be updated regularly whenever the genomes of newly isolated Alternaria spp. are available. The citrus-related Alternaria genomes database is open accessible through the Citrus Fungal Disease Database.[ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Methionine is a unique sulfur-containing amino acid, which plays an important role in biological protein synthesis and various cellular processes. Here, we characterized the biological functions of AaMetB, AaMetC, and AaMetX in the tangerine pathotype of Alternaria alternata. Morphological analysis showed that the mutants lacking AaMetB, AaMetC, or AaMetX resulted in less aerial hypha and fewer conidia in artificial media. Pathogenicity analysis showed that AaMetB, AaMetC, and AaMetX are required for full virulence. The defects in vegetative growth, conidiation and virulence of ▵MetB, ▵MetC, and ▵MetX can be restored by exogenous methionine and homocysteine, indicating that AaMetB, AaMetC, and AaMetX are required for methionine biosynthesis. However, exogenous cysteine only restored the growth and virulence defects of ▵MetR but not ▵MetB/C/X, suggesting that AaMetR is essential for cysteine biosynthesis. Oxidant sensitivity assay showed that only ▵MetR is sensitive to H₂O₂ and many ROS-generating compounds, indicating that AaMetR is essential for oxidative tolerance. Interestingly, fungicides indoor bioassays showed that only the ▵MetR mutants are susceptive to chlorothalonil, a fungicide that could bind to the cysteine of glyceraldehyde-3-phosphate dehydrogenase. Comparative transcriptome analysis showed that the inactivation of MetB, MetC, MetX, or MetR significantly affected the expression of methionine metabolism-related genes. Moreover, the inactivation of AaMetR significantly affected the expression of many genes related to glutathione metabolism, which is essential for ROS tolerance. Taken together, our study provides genetic evidence to define the critical roles of AaMetB, AaMetC, AaMetX, and AaMetR in cysteine and methionine metabolism, fungal development and virulence of Alternaria alternata. IMPORTANCE The transcription factor METR regulating methionine metabolism is essential for reactive oxygen species (ROS) tolerance and virulence in many phytopathogenic fungi. However, the underlying regulatory mechanism of METR involved in this process is still unclear. In the present study, we generated AaMetB, AaMetC and AaMetX deletion mutants and compared these mutants with AaMetR disrupted mutants. Interestingly, we found that AaMetB, AaMetC and AaMetX are required for vegetative growth, conidiation, and pathogenicity in Alternaria alternata, but not for ROS tolerance and cysteine metabolism. Furthermore, we found that METR is involved in the biosynthesis of cysteine, which is an essential substrate for the biosynthesis of methionine and glutathione. This study emphasizes the critical roles of MetR, MetB, MetC, MetX in the regulation of cysteine and methionine metabolism, as well as the cross-link with glutathione-mediated ROS tolerance in phytopathogenic fungi, which provides a foundation for future investigations.

Municipal wastewater treatment plants (WWTPs) serve as global repositories for diverse and dynamic microbial communities, reflecting the complex interplay of human activities, environmental conditions, and public health challenges. Despite their importance, a comprehensive understanding of the global distribution, composition, and functional roles of these microbial ecosystems has remained elusive. Here, we present a comprehensive analysis of bacterial and viral diversities in global wastewater systems by examining 575 sampling sites across 74 cities in 60 countries. Through metagenomic analysis, we reconstructed 12,758 non-redundant bacterial metagenome-assembled genomes (MAGs) spanning 70 phyla, with 4,499 MAGs representing novel species. Despite considerable regional variation, we identified a consistent core microbiome present across 70% of global samples predominantly comprising Proteobacteria. We further assembled 1.7 million viral genomes, revealing unprecedented viral diversity with over 1.5 million species-level viral operational taxonomic units (vOTUs). Network analysis demonstrated that transport proteins play crucial roles in maintaining WWTP functional resilience against disturbances. Machine learning approaches effectively predicted continental origins of wastewater samples based on microbial signatures, confirming that microbial communities reflect local environmental and socioeconomic conditions while maintaining functional conservation. We observed significant variation in the antibiotic resistance gene (ARG) distribution, with elevated prevalence in certain African and Asian regions compared to Europe and North America. Our results establish wastewater microbiomes as important indicators of human activity and provide critical insights for advancing environmental monitoring, antimicrobial resistance surveillance, and wastewater-based epidemiology. IMPORTANCE: Intensifying urbanization and human activities have dramatically increased global wastewater generation, creating complex microbial ecosystems that significantly impact environmental and public health. This study presents the first large-scale, comprehensive characterization of bacterial and viral communities in wastewater treatment systems worldwide. By analyzing samples from diverse geographical, climatic, and socioeconomic contexts, we reveal how wastewater microbiomes serve as microbial fingerprints of human society, reflecting regional characteristics while maintaining functional conservation. Our findings demonstrate that these communities function as ecological extensions of human gut microbiota in the external environment, with important implications for the spread of antibiotic resistance and pathogens. The identification of viruses as key metabolic regulators in these systems provides new perspectives on microbial community dynamics. This global-scale analysis advances our understanding of wastewater microbiology and offers valuable insights for improving wastewater management, enhancing environmental monitoring systems, and strengthening public health surveillance through wastewater-based epidemiology.