Magnaporthe oryzae is one of the most devastating pathogenic fungi that affects a wide range of cereal plants, especially rice. Rice blast disease causes substantial economic losses around the globe. The M. oryzae genome was first sequenced at the beginning of this century and was recently updated with improved annotation and completeness. In this review, key molecular findings on the fungal development and pathogenicity mechanisms of M. oryzae are summarized, focusing on fully characterized genes based on mutant analysis. These include genes involved in the various biological processes of this pathogen, such as vegetative growth, conidia development, appressoria formation and penetration, and pathogenicity. In addition, our syntheses also highlight gaps in our current understanding of M. oryzae development and virulence. We hope this review will serve to improve a comprehensive understanding of M. oryzae and assist disease control strategy designs in the future.

Nuclei define eukaryotes, enabling macromolecular compartmentalization and cellular regulation. Each nucleus is believed to contain one or more haploid sets of chromosomes (1N). However, we discovered that haploid cells of the pathogenic fungi Sclerotinia sclerotiorum and Botrytis cinerea distribute their chromosomes such that each of their nuclei contains only a subset of the haploid chromosomes (≤½N). The unusual chromosomal distribution was confirmed by cellular and molecular methods including chromosome counting, fluorescence in situ hybridization, flow cytometry–based DNA measurements, and single-nucleus polymerase chain reaction experiments. This phenomenon challenges fundamental assumptions about nuclear organization and opens fresh avenues in chromosome biology.

Sclerotinia sclerotiorum is a phytopathogenic soilborne fungus that damages diverse crops worldwide. It has recently been discovered that this fungus distributes its 16 chromosomes irregularly between two nuclei within each haploid ascospore. Here, we study the meiotic process by tracking phenotypic segregation and recombination events in the progeny of a strain resulting from the fusion of two morphologically distinct mutants. We show that, despite the unusual chromosomal distribution into two nuclei, chromosome segregation and genetic recombination occur normally in S. sclerotiorum, likely due to a tight coordination between the two complementing nuclei during meiosis. Consistently, an atypical ascospore development process deviating from the conventional model was observed. Furthermore, we show that our co-segregation analyses method can be used to identify causal mutations in uncharacterized mutants, uncovering a role for deubiquitination in fungal development and virulence.

Sclerotinia sclerotiorum is a notorious soilborne fungal pathogen that causes white mold in a wide range of host plants, leading to globally significant yield loss in many crops. Hydrophobins (HPs) are small, secreted proteins unique to filamentous fungi, with diverse roles in fungal biology. However, their functions in S. sclerotiorum remain poorly understood. Here, we systematically investigated the roles of three HP genes, SsHP1, SsHP2, and SsHP3, through reverse genetic analyses. By analyzing their deletion mutant phenotypes, we demonstrate that class I HP (SsHP1) is specifically required for proper sclerotia development, whereas class II HPs (SsHP2 and SsHP3) are essential for compound appressoria functionality. All three HPs contribute to fungal surface hydrophobicity, cell wall integrity, and stress tolerance. Using mycelial fusion, we generated double mutants lacking both class II HPs, which exhibited more severe defects in appressoria development, virulence, cell wall integrity, and stress adaptation, indicating their partially redundant roles. SsHP2 is required for both host penetration and post-penetration virulence, whereas SsHP3 mainly affects host penetration, revealing their overlapping yet distinct contributions to pathogenic development. Although all HP mutants formed normal apothecia and asci, they released significantly fewer ascospores, suggesting that HPs are dispensable for sexual morphogenesis but crucial for the biophysical process of ascospore dispersal. Furthermore, carbohydrate analyses uncovered that these HPs affect cell wall composition, more broadly influencing stress adaptation and virulence. Taken together, our study reveals both conserved and divergent roles of HPs across fungi and highlight their multifaceted contributions to S. sclerotiorum biology, offering new perspectives for disease management.

The nucleus is a defining feature of eukaryotic cells, compartmentalizing the genome to enable precise regulation of diverse cellular processes. The long-standing paradigm in textbooks states that each nucleus carries at least a complete haploid genome —the “one nucleus, one whole genome” rule. A striking exception was recently uncovered: in two sclerotia-forming plant pathogenic fungi in the Sclerotiniaceae family, Sclerotinia sclerotiorum and Botrytis cinerea , haploid chromosomes are irregularly distributed across multiple nuclei. However, whether such phenomenon occurs in other eukaryotes, particularly in non-pathogenic fungi, is unclear. Through a literature survey, we identified many fungi that can potentially also separate their haploid chromosomes across different nuclei. Interestingly, Neurospora crassa , a foundational fungal genetics model, came out as a candidate. Its conidia, typically containing two or three nuclei, were believed to harbor a complete haploid genome within each nucleus. However, using approaches including chromosome counting, flow cytometry, and fluorescence in situ hybridization, we found that haploid chromosomes in N. crassa can be unevenly distributed among multiple nuclei. These findings challenge longstanding assumptions in fungal genetics and provide new directions for investigating genome organization. Our results indicate that the organisms violating the “one nucleus, one whole genome” rule are beyond sclerotia-forming pathogenic fungi. Since over 90% of fungi have not even been described, we propose that many more of them may likewise partition their genomes non-uniformly across nuclei, a process that could facilitate their adaptation and evolution.

Sclerotinia sclerotiorum is a broad-spectrum soilborne fungal pathogen, causing substantial yield losses in crops worldwide. Auxiliary Activity Family 5 (AA5) copper radical oxidases (CROs) are members of the carbohydrate active enzymes (CAZymes), valued for their potential as biocatalysts. Although they were reported to contribute to fungal development and disease progression in some phytopathogenic fungi such as Colletotrichum graminicola, the roles of AA5 enzymes in S. sclerotiorum remain largely unexplored. Here, we systematically investigated S. sclerotiorum AA5 genes through reverse genetics and biochemical approaches. Phylogenetic analysis grouped the S. sclerotiorum AA5 proteins into two subfamilies, including three subfamily 1 (AA5_1) members and one subfamily 2 (AA5_2) member. Enzymatic characterization revealed that one AA5_1 enzyme, SsAA5c, exhibited the highest catalytic specificity towards D-glyceraldehyde compared with methylglyoxal and glycerol. In addition, a predicted peroxidase gene (SsPX1) was identified in tandem with the putative AA5_2 gene, SsAA5d. Phenotypic analysis of gene deletion mutants demonstrated that these genes differentially affect fungal development and virulence. While their exact physiological substrates await identification, our findings highlight important roles of AA5 oxidases and the associated peroxidase in the biology of S. sclerotiorum, providing insights that may contribute to future improved disease management strategies.