How Asparagus Stems Fight Off Infection from a Common Plant Disease

Jenn Hoskins
6th July, 2024

How Asparagus Stems Fight Off Infection from a Common Plant Disease

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Henan Normal University studied how the fungus Phomopsis asparagi infects asparagus stems
  • The fungus starts by germinating on the stem surface and penetrates the host cell wall within one day
  • By 3-5 days, the fungus spreads inside and between cells, causing significant cellular damage
  • The asparagus plant responds by producing callose analogs and reactive oxygen species to defend against the infection
Asparagus stem blight is a serious threat to asparagus cultivation worldwide, caused by the fungus Phomopsis asparagi. Despite its destructive impact, the mechanisms behind P. asparagi's infection and pathogenesis have been poorly understood. A recent study conducted by researchers at Henan Normal University aims to shed light on this issue by examining the infection process at the cytological and ultrastructural levels[1]. The study revealed that P. asparagi conidia begin to germinate at either the tip or the middle, producing short germ tubes on the asparagus stem surface within 20 hours post-inoculation (hpi). These germ tubes then penetrate the host cell wall using appressorium-like structures or narrow pegs within one day post-inoculation (dpi). By 3-5 dpi, a significant number of P. asparagi hyphae colonize the epidermal cells, growing both inside and between cells. The movement of hyphae between cells is facilitated by constricted invasive hyphae pegs, and they exhibit bidirectional intracellular growth, extending along the inner side of the cell wall towards the stem cortex and central cylinder. This colonization results in cellular damage characterized by plasmolysis, cell wall rupture, and cytoplasmic disruption. By 11 dpi, the fungi penetrate the parenchyma cells, forming fungal pycnidia and releasing conidia by 13 dpi. The host defense response was also investigated, revealing a reduced germination rate of conidia, formation of callose analogs, and a reactive oxygen burst. These findings provide new insights into the infection process and host response in P. asparagi-plant interaction. The study's findings align with earlier research on plant-pathogen interactions. For instance, the role of reactive oxygen species (ROS) in plant defense is well-documented. ROS are not only involved in direct antimicrobial activity but also serve as signaling molecules that trigger further defense responses[2]. The formation of callose analogs, a plant defense mechanism, is also consistent with previous findings that highlight the importance of physical barriers in preventing pathogen invasion[3]. Furthermore, the study's observation of hyphal growth and cell-to-cell movement through narrow pegs is reminiscent of the infection strategies employed by other fungal pathogens. For example, the hemibiotrophic fungus Magnaporthe oryzae, which causes rice blast disease, also uses invasive hyphae to move between cells, often co-opting plant structures like plasmodesmata for cell-to-cell movement[4]. This suggests that similar mechanisms may be at play in different plant-pathogen interactions. The study also contributes to our understanding of the role of fungal structures in pathogenesis. The formation of appressorium-like structures and narrow pegs for host cell wall penetration is similar to the infection cushions (IC) formed by the necrotrophic fungus Botrytis cinerea, which produces various enzymes and toxins to facilitate plant penetration and colonization[5]. This parallel further underscores the complexity and adaptability of fungal pathogens in overcoming plant defenses. In summary, the study by Henan Normal University provides valuable insights into the infection mechanisms of P. asparagi and the corresponding host responses in asparagus. By elucidating the cytological and ultrastructural aspects of this interaction, the research not only enhances our understanding of asparagus stem blight but also contributes to the broader field of plant-pathogen interactions. These findings could inform future strategies for developing disease-resistant asparagus varieties, potentially mitigating the impact of this devastating disease on global asparagus cultivation.

AgricultureBiochemPlant Science

References

Main Study

1) Cytological and ultrastructural investigation of pathogen infection pathway and host responses in asparagus stem infected by Phomopsis asparagi

Published 4th July, 2024

https://doi.org/10.1186/s42483-024-00252-x

Related Studies

2) ROS are evolutionary conserved cell-to-cell stress signals.

https://doi.org/10.1073/pnas.2305496120

3) Pathogenesis-related proteins and peptides as promising tools for engineering plants with multiple stress tolerance.

https://doi.org/10.1016/j.micres.2018.04.008

4) Roles for rice membrane dynamics and plasmodesmata during biotrophic invasion by the blast fungus.

Journal: The Plant cell, Issue: Vol 19, Issue 2, Feb 2007

5) The infection cushion of Botrytis cinerea: a fungal 'weapon' of plant-biomass destruction.

https://doi.org/10.1111/1462-2920.15416


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