Pathogenic Mechanisms of Acidovorax Species in Cucurbit Crops

Acidovorax species, notably Acidovorax citrulli, employ a multifaceted arsenal to infect cucurbit hosts. Central to their strategy is the type III secretion system (T3SS), a needle-like apparatus that injects an array of type III effectors (T3Es) into plant cells. These effectors manipulate host immunity by suppressing reactive oxygen species (ROS) bursts, altering hormone signalling and targeting defence-related transcription factors. Biofilm formation on leaf and seed surfaces enhances epiphytic survival and facilitates entry through stomata or wounds. Motility structures such as flagella and type IV pili (T4P) contribute to colonisation, twitching motility and interbacterial competition. Regulation of virulence genes by HrpG/HrpX ensures coordinated expression of T3SS components and effectors in response to plant cues. Host specificity is determined by effector repertoires and subtle variations in cell-surface structures, including lipopolysaccharide and secreted enzymes that degrade cell-wall polymers. Seed transmission underpins long-distance spread, while environmental factors such as moisture influence epiphytic persistence. Understanding of these mechanisms underpins efforts to breed resistant cultivars and to devise targeted interventions, such as effector-informed diagnostics and chemical or biological control agents that disrupt secretion, adhesion or biofilm development.

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Pathogenic Mechanisms of Acidovorax Species in Cucurbit Crops publication trend

The graph below shows the total number of articles in pathogenic mechanisms of acidovorax species in cucurbit crops across all publications each year (not limited to Nature Index journals).

Technical terms

Type III secretion system (T3SS): A specialised bacterial apparatus that injects effector proteins directly into host cells to manipulate their defences and physiology.

Type III effectors (T3Es): Secreted proteins delivered by the T3SS that target host immune components or signalling networks.

Type IV pili (T4P): Filamentous surface structures involved in bacterial attachment, twitching motility and biofilm development.

Reactive oxygen species (ROS): Highly reactive molecules produced by host cells as an early defence against invading pathogens.

PAMP-triggered immunity (PTI): The basal plant defence response activated upon recognition of conserved microbial molecules known as pathogen-associated molecular patterns (PAMPs).

Biofilm: A structured community of bacterial cells enclosed in a self-produced extracellular matrix that enhances survival on surfaces and resistance to stress.

References

1. Acidovorax citrulli type III effector AopU interferes with plant immune responses and interacts with a watermelon E3 ubiquitin ligase. Frontiers in Microbiology (2023).
2. pilA Gene Contributes to Virulence, Motility, Biofilm Formation, and Interspecific Competition of Bacteria in Acidovorax citrulli. Microorganisms (2023).
3. Show me your secret(ed) weapons: a multifaceted approach reveals a wide arsenal of type III‐secreted effectors in the cucurbit pathogenic bacterium Acidovorax citrulli and novel effectors in the Acidovorax genus. Molecular Plant Pathology (2019).
4. Involvement of hrpX and hrpG in the Virulence of Acidovorax citrulli Strain Aac5, Causal Agent of Bacterial Fruit Blotch in Cucurbits. Frontiers in Microbiology (2018).
5. Acidovorax citrulli Type III Effector AopP Suppresses Plant Immunity by Targeting the Watermelon Transcription Factor WRKY6. Frontiers in Plant Science (2020).