Aug 2026· Fungal Genetics and Biology· Vol 185, pp.
104105
· 0 citations· 40 references
Medicine
TL;DR
It is demonstrated that AaAtg4 is important for spore germination, siderophore biosynthesis, iron acquisition, oxidative stress resistance, and toxin production, thereby establishing its critical role in A. alternata virulence.
Abstract
The tangerine pathotype of Alternaria alternata infects multiple citrus cultivars, causing brown spot disease. The role of autophagy in toxin production and siderophore biosynthesis remains to be further confirmed. This study identifies autophagy-related protein 4 (AaAtg4) as a critical regulator of fungal growth, development, stress resistance, iron homeostasis, and virulence, as determined by genetic and biochemical analyses. Targeted deletion of the AaAtg4 gene using split-marker recombination generated two ΔAaAtg4 mutants, which displayed reduced growth on minimal medium, impaired conidiation, delayed germination, and diminished formation of appressorium-like structures compared with the wild-type strain. The mutants were hypersensitive to hydrogen peroxide and iron stress, highlighting the roles of AaAtg4 in oxidative stress tolerance and iron metabolism. ΔAaAtg4 mutant strains failed to produce detectable siderophores and exhibited downregulation of siderophore production-related genes (AaHapX, AaNps6, AaMirB) alongside upregulation of the AaSreA gene encoding a siderophore repressor. Toxin profiling further revealed altered host-selective toxin production, with distinct shifts in retention times in ΔAaAtg4 compared to the wild-type strain. However, AaAtg4, but not autophagy itself, was required for toxin production, as deletion of other autophagy-related genes had no effect. Reintroduction of functional AaAtg4 into a ΔAaAtg4 mutant rescues all defects, confirming that the loss of AaAtg4 function directly causes the observed phenotypes. These findings demonstrate that AaAtg4 is important for spore germination, siderophore biosynthesis, iron acquisition, oxidative stress resistance, and toxin production, thereby establishing its critical role in A. alternata virulence.
Verticillium dahliae
is a soilborne fungal pathogen that causes Verticillium wilt in cotton and many other crops. While siderophore-associated iron acquisition is recognized as crucial, its precise connections to fungal development, stress adaptation, and host colonization remain incompletely elucidated. This study identifies the VdOMO protein as a putative SidA-family L-ornithine N5-monooxygenase through phylogenetic and pairwise sequence analyses. Analyses of independent deletion mutants and a complemented strain showed that
VdOMO
contributes to conidial morphology and production, microsclerotium formation, and melanization, growth on selected carbon sources, cell wall integrity, and adaptation to alkaline, salt, and oxidative stresses. Although final visible disease symptoms were comparable among inoculated groups,
ΔVdOMO
mutants exhibited reduced vascular browning, diminished fungal biomass accumulation at early infection stages, and impaired cellophane penetration. A representative
ΔVdOMO
mutant also displayed decreased biomass-normalized extracellular chrome azurol S (CAS)-reactive iron-chelating activity and intracellular iron accumulation, both of which were restored to wild-type levels upon complementation. Furthermore,
VdOMO
deletion was linked to iron-condition-dependent alterations in the expression of genes involved in iron regulation, siderophore biosynthesis, and siderophore transport. Collectively, these findings underscore a significant role for
VdOMO
in siderophore-associated iron acquisition, fungal development, stress adaptation, and the early stages of host colonization in
V. dahliae
.
Yusha Du, Lixinyu Sun, Kangwei Xie et al.· Frontiers in Plant Science· 0 citations
Introduction Autophagy-related protease AaAtg4 was previously identified as a key regulator in the pathogenic fungus Alternaria alternata, orchestrating a complex interplay among autophagy, oxidative stress resistance, iron homeostasis, and ACT toxin biosynthesis. The underlying mechanisms of AaAtg4 in relation to oxidative stress response remain unknown. Methods Genetic and biochemical analyses. Results In this study, we examined the effect of hydrogen peroxide (H₂O₂) on AaAtg4. Functioning as a cysteine protease, AaAtg4 directly interacts with the AaAtg8 ubiquitin-like protein and is indispensable for AaAtg8 processing and autophagosome formation, with its enzymatic activity modulated by oxidative cues. H₂O₂ differentially impacts AaAtg4 activity, phosphorylation, binding with AaAtg8, AaAtg8 lipidation/delipidation, and autophagy. H₂O₂ has biphasic effects on AaAtg4. Moderate H₂O₂ levels enhance AaAtg4 activity and autophagy, whereas excessive H₂O₂ suppresses both, revealing a threshold-dependent redox regulation. Furthermore, AaAtg4 interacts with the stress-responsive mitogen-activated protein kinase AaHog1, which modulates its phosphorylation under conditions less conducive to autophagy and thus, reinforces a dynamic signaling axis. Discussion These findings indicate that H₂O₂ has multifaceted effects on AaAtg4 in a dosage-dependent or threshold-specific manner. These regulatory mechanisms may position AaAtg4 as a central integrator of cellular stress responses and secondary metabolism, thereby advancing our understanding of fungal pathogenicity and environmental adaptation.
Hsin-Yu Lu, Je-Jia Wu, C. H. Y. Choo et al.· Frontiers in Fungal Biology· 0 citations
A physical interaction is identified between AaSlt2 and Swi6/RlmA, suggesting that these components are critical for cell wall synthesis, which advances the understanding of pathogenic mechanisms of A. alternata and proposes potential strategies for controlling postharvest diseases.
Rong Li, Yiyang Liu, Li Li et al.· Virulence· 0 citations
Trichothecium roseum is a highly destructive postharvest pathogenic fungus that causes pink mold rot in various fruit and leads to significant agricultural and economic losses. Phytoene is crucial for phytopathogens, but the molecular mechanism by which the phytoene synthase gene crtB regulates fungal pathogenicity remains largely unclear. In this study, we evaluated the functions of TrcrtB a phytoene synthase, in T. roseum via in vivo and in vitro assays. Our results showed that knock-out of TrcrtB showed inhibition of production of phytoene and its relevant downstream metabolites, such as lycopene, carotenes and carotenal, resulting in colorless colony and branching at the mycelial edges in the knockout mutant ΔTrcrtB. Compared with the wild type (WT) strain, the colony expansion was significantly reduced 35% at 5 days post-inoculation (dpi), and conidiation was notably decreased to 45%, 36%, and 70% at 3, 5, and 7 dpi in ΔTrcrtB in vitro. Scanning electron microscope observation revealed similar results. Moreover, the ΔTrcrtB showed higher sensitivity to abiotic stresses than WT, as evidenced by inhibition rates of ΔTrcrtB colony expansion up to 71.76% (menadione), 47.73% (Congo red), 23.01% (SDS), and 17.13% (KCl). The pathogenicity of ΔTrcrtB was dramatically impaired by decreasing the rotten area up to 85.26% on apple fruit and 70.30% on pears fruit. These results suggest that TrcrtB and phytoene are critical for development, stress tolerance and pathogenicity of T. roseum. Collectively, our study highlights the roles of TrcrtB and phytoene in the pathogenic fungus T. roseum, providing new insights into the molecular mechanisms of pink rot pathogenesis.
Fusarium proliferatum causes rice spikelet rot and contaminates grains with fumonisins. Here, we report that the methyltransferase FpLaeA is a global regulator essential for its pathogenicity. Deletion of FplaeA impaired conidiation and led to conspicuous accumulation of β-1,3-glucan. The ΔFplaeA mutant failed to produce fumonisin B1 (FB1), accompanied by the downregulation of the biosynthetic gene cluster, depletion of the precursor alanine, and disruption of sphingolipid homeostasis. It also showed defective invasive hyphal growth and attenuated secretion of pectate lyase (PL) and polygalacturonase (PG). Crucially, infection by ΔFplaeA triggered an activation of jasmonic acid (JA)-mediated defenses, evidenced by elevated JA levels and upregulated expression of JA biosynthetic genes. Our findings position FpLaeA as a key coordinator of fungal pathogenesis and immune evasion, highlighting its potential as a target for integrated control of F. proliferatum and its associated mycotoxin risk.
Ling Wang, Shaoqing Tang, Weiyang Liao et al.· Journal of Agricultural and...· 0 citations
Fusarium graminearum, the major pathogen causing maize ear rot, severely threatens food security. Targeted gene deletion was used to characterize physiological functions of FgSRE1 in this pathogen. Transcriptomic profiling was conducted on axenic wild-type and ΔFgSRE1 cultures, plus maize ear tissues colonized by both strains. Nine core DEGs functionally annotated to transmembrane transport, membrane homeostasis and oxidative stress pathways were selected for qRT-PCR validation, including four upregulated genes encoding putative transferases and five downregulated transporter genes. Phenotypic assays revealed that the ΔFgSRE1 mutant displayed severe defects in conidial and ascospore production, along with drastically weakened pathogenicity on maize ears and leaves versus wild-type and complemented strains. qRT-PCR analysis confirmed consistent expression trends with the RNA-seq data: four putative transferase-encoding genes were up-regulated, whereas five genes related to membrane and redox transport were repressed. Together, the genetic and phenotypic results demonstrate that FgSRE1 contributes to reproductive development and virulence in F. graminearum, whereas the transcriptomic data suggest potential associations with metabolic, redox, and membrane-transport-related pathways. Our findings provide a basis for investigating the FgSRE1-associated virulence network and developing eco-friendly maize ear rot control strategies.
Lin-Ru Shen, Hongyan Hui, Lei Guo et al.· Journal of Fungi· 0 citations