Pathogen-Host Interactions in Alternaria Fungi

Alternaria species are necrotrophic fungi that colonise a broad range of plant hosts, causing economically significant diseases such as early blight of potato, brown spot of citrus and leaf spot in solanaceous and cucurbit crops. Pathogenicity relies on the coordinated production of host-selective toxins (HSTs), non-host-selective toxins and an arsenal of cell-wall-degrading enzymes that breach plant barriers. Upon contact, fungal spores germinate and secrete small secreted proteins and secondary metabolites that suppress local defences, induce reactive oxygen species (ROS) bursts and lead to programmed cell death in susceptible tissues. The fungus employs specialised mechanisms to detoxify ROS, including catalases, peroxidases and transporters, thereby overcoming oxidative stress imposed by the host. Conditionally dispensable chromosomes (CDCs) often carry HST gene clusters and effector-encoding loci, enabling rapid host adaptation and horizontal transfer of virulence determinants among strains. Advances in genomics, transcriptomics and proteomics have revealed dynamic regulatory networks involving mitogen-activated protein kinases, transcription factors such as Yap1 and Skn7, and epigenetic modulators that fine-tune toxin biosynthesis, spore formation and infection structure development. Understanding these interactions informs the development of resistant cultivars and targeted control measures, including interference with toxin pathways and enhancement of plant immunity.

Research from Nature Portfolio

Foundational genomic and transcriptomic investigations of the tangerine pathotype of Alternaria alternata have elucidated the genetic architecture and stress-response mechanisms critical for pathogenicity. High-quality genome assembly uncovered the complete cluster of genes responsible for the biosynthesis of the A. citri toxin, including several pathotype-specific metabolic enzymes. Global expression profiling under oxidative challenge revealed induction of antioxidant systems—catalase, peroxiredoxin, thioredoxin and glutathione pathways—and upregulation of transporters and heat-shock proteins. These findings established how the fungus balances toxin production with robust ROS detoxification to sustain growth within host tissues and pinpointed candidate genes for targeted disruption of virulence.

Pathogen-Host Interactions in Alternaria Fungi publication trend

The graph below shows the total number of articles in pathogen-host interactions in alternaria fungi across all publications each year (not limited to Nature Index journals).

Technical terms

Host-selective toxin (HST): A low-molecular-weight secondary metabolite that targets specific plant genotypes, determining host range and contributing directly to necrosis.

Reactive oxygen species (ROS): Highly reactive molecules generated by the host as a defence response; pathogens deploy antioxidant systems to neutralise ROS and maintain infection.

Conditionally dispensable chromosome (CDC): An accessory chromosome present in some strains that carries virulence genes and can be gained or lost without affecting core viability.

Carbohydrate-active enzymes (CAZymes): A diverse group of secreted enzymes that degrade plant cell wall polysaccharides, facilitating tissue penetration.

Effector: A secreted protein that modulates host immunity or cellular processes to favour pathogen establishment and proliferation.

References

1. Genomic characterization of the conditionally dispensable chromosome in Alternaria arborescens provides evidence for horizontal gene transfer. BMC Genomics (2012).
2. A Major Facilitator Superfamily Transporter-Mediated Resistance to Oxidative Stress and Fungicides Requires Yap1, Skn7, and MAP Kinases in the Citrus Fungal Pathogen Alternaria alternata. PLOS ONE (2017).
3. Genomic and transcriptomic analyses of the tangerine pathotype of Alternaria alternata in response to oxidative stress. Scientific Reports (2016).
4. Transcriptome sequencing leads to an improved understanding of the infection mechanism of Alternaria solani in potato. BMC Plant Biology (2023).
5. Multi-omics approaches to understand pathogenicity during potato early blight disease caused by Alternaria solani. Frontiers in Microbiology (2024).
6. A Cytochrome P450 AaCP1 Is Required for Conidiation and Pathogenicity in the Tangerine Pathotype of Alternaria alternata. Microorganisms (2025).